Gypsum mold for clay. How to remove a plaster mold from a figure. Casting a model from rough molds
Clay casting
Page 19 of 25
Clay casting
Among the various methods of molding ceramic products, casting occupies a special place. It makes it possible to produce with great precision many identical thin-walled vessels with complex shapes, small sculptures with fine detail. Clay, or slip, casting is based on the property of gypsum to absorb moisture and the property of clay to release moisture.
Slip is clay diluted to a fluid state, reminiscent of thick cream in consistency.
The gypsum mold into which the slip is poured intensively absorbs water. In this case, a layer of clay mass of equal thickness is evenly distributed over the internal surfaces of the mold, forming the walls of the future product, or, as ceramists say, a shard. After drying, the hollow clay product is removed from the mold and dried before being fired. This is, in general terms, the scheme of clay (slip) casting. Direct casting is preceded by a lot of preparatory work. It is necessary to make a sketch and make a model of the future product based on it, and then cast a casting mold from plaster according to the model.
You should start developing a sketch only after you clearly understand the purpose of the product being developed, because shape, proportions, size and decorative finishing are closely related to it. But keep in mind that no matter how successful the sketch is, when making a three-dimensional item based on it, there is almost always a need to make some adjustments. Thus, direct work on a three-dimensional model can prompt the artist to make decisions that cannot always be predicted in a sketch. In production, sometimes there is a division of labor, when the sketch is carried out by an artist, and the model is turned by a master model maker. To ensure that the creative process is not interrupted, the artist must be able to grind or cut out models himself.
The model can be made of wood or plaster. Models are turned from wood on a lathe or made with carpentry and carving tools.
The turned and cut parts are connected into a single whole using nails, screws and waterproof glue, such as BF-2 or epoxy resin. The finished model is soaked several times in hot drying oil and dried. Plaster models are turned on a special grinding machine, which is essentially a pottery wheel, with stepped supports located on the right and left sides (Fig. 33.1a).
During turning, a wooden straightening rod (33.1b) is placed on the steps. The rule serves as a support for the cutter when turning the model. If you connect an electric motor to a pottery wheel, it can be used as a sharpening machine. Several slats are stuffed onto the upper disk and formwork made of waterproof cardboard impregnated with drying oil or paraffin (33.1c) is tied around the perimeter with twine. Gypsum (33.1g) is poured into the formwork. Thus, after the gypsum has hardened and the formwork has been removed, a massive cylindrical blank is formed on the disk - the head of the grinding machine (33.1d). The head is positioned so that during operation the rotating model is approximately at eye level of the sharpener. Just as when pulling a clay product on a pottery wheel, the disk should rotate counterclockwise at a speed of 300-350 rpm. According to the principle of operation, the sharpening machine resembles a lathe: chips are also gradually removed from the rotating workpiece with cutters until the desired configuration of the rotating body is obtained. But unlike a lathe, the gypsum blank is positioned vertically, not horizontally.
Thanks to this, it is convenient to cast the workpiece directly on the head of the sharpening machine; in addition, the master sees the product in its natural position, that is, the same as if it were standing on the table. In the process of searching or refining a form, this is very important. The cutters for the pattern-grinding machine are called clubs (33.2b). Clubs are made from steel rods that are mounted on wooden handles. A steel plate in the shape of a triangle, rhombus, trapezoid, shaft, etc. is attached to the end of the rod at a right angle. Since the material being processed is quite soft, there is no need to harden the cutting parts of the cutters. Some cutters can be made from thick wire, the end of which is flattened and bent with a hook. Similar clubs are used when turning clay products on a pottery wheel.
When determining the dimensions of the model, and therefore the workpiece, it is necessary to take into account that the clay casting after drying and then after firing is reduced by a total of 10-15%. In order for the ceramic product to have the dimensions previously planned in the sketch after drying and firing, the model for its shape should be made larger, taking into account the percentage of shrinkage, which is determined experimentally. If it is known in advance, the dimensions of the plaster or wooden model are determined by the formula: X = 100 x a/100 - b, where a is the size of the ceramic product after drying and firing, b is air and firing shrinkage as a percentage. Let us assume that the height of the finished ceramic product should be 250 mm with a 10% shrinkage of the clay mass. Using the formula, we determine that the height of the plaster model should be equal to 276 mm. If you deal with the same clay constantly, then the shrinkage will always be constant. In these cases, a scale compass made of two steel strips (33.2a) can be used to determine the dimensions of the model. Bend the ends of the compass so that the distances between them have certain proportional relationships, which are established experimentally. The opening of the compass on one side must correspond to the actual dimensions of the clay casting, on the other - to the size that must be taken on the model. Having prepared the machine and tools, install a shell on the gypsum head in the form of a cylinder, rolled up from thick cardboard or roofing felt impregnated with drying oil (33.3a). Secure the cylinder with soft wire or sew with thick threads.
The height of the shell should correspond to the height of the model being turned, and the diameter should correspond to the largest diameter of the model with a small allowance.
Fill the formwork attached to the head of the grinding machine to the top with gypsum solution (7 parts gypsum to 10 parts water). As soon as the gypsum hardens after 8-10 minutes, remove the formwork and, having marked all the main dimensions with a pencil (33.3b), begin turning the model. Place the straightener on the upper steps, rest the stick on it and begin to remove the shavings from the rotating plaster blank (ZZ.Zv).
Moisture-saturated gypsum is cut very easily. It should be kept wet until turning is completed. When drying, the plaster should be moistened with a sponge soaked in water. Having achieved the desired configuration of the model, cut it off at the base with steel wire, and then dry it at room temperature for 2-3 days. The dried model is impregnated several times with drying oil or epoxy resin diluted with acetone. It takes at least two more days for the model to dry. The model serves as the basis for making a plaster casting mold. The simplest plaster mold consists of two halves. Before you start casting the mold, make a shallow hemispherical cutout on the bottom side of the base of the model. This will ensure the stability of the future casting. Install the roofing felt formwork on a flat panel, having previously lubricated its internal surfaces with release agent (Fig. 34).
Prepare a release lubricant from two parts paraffin and five parts kerosene, melted in a water bath. Having completed the preparation, pour a layer of gypsum 10-15 mm thick into the formwork (34.1). As soon as the plaster sets, but does not lose its plasticity - after about 1.5-2 minutes - install the model inside the formwork, pressing its base into the soft plaster. Then add gypsum to the formwork so that the solution is level with the most convex areas of the model.
Remember that if the level of gypsum mortar is raised above the most convex points, the model will not be able to be removed from the bottom of the mold.
After removing the formwork, use a knife to cut a rebate (quarter) along the entire perimeter, which will later form part of the interlocking connection between the two halves of the gypsum casting mold (34.2). Lubricate the cut planes with release agent and place them back into the formwork, which now needs to be filled to the top with gypsum mortar (34.3). After the gypsum has hardened, remove the formwork and apply a mark (34.3a) on the side surface, running along its axis and intersecting both halves of the form. This is necessary so that when assembling the mold you can quickly and accurately connect one half to the other. After applying the marks, the hardened halves of the mold are separated and the model is removed from it (34.4). The mold needs to be dried without the model for two to three days. It will dry much faster if you dry it near the stove or central heating radiator. The form is ready. Now you need to prepare a slip - exhausted liquid clay. The method of elutriating clay is described at the very beginning of the book.
Clay casting. Fill the slip into a well-dried plaster mold to the top (Fig. 35.1). Porous plaster will immediately begin to absorb moisture from it. This is easy to guess by how quickly the slip level in the mold drops. By absorbing moisture, gypsum attracts the smallest particles of clay suspended in the slip to the surface of the mold. Gradually, a fairly dense layer of clay mass forms on the walls of the mold.
The process of absorption of moisture with the simultaneous growth of a clay layer on the walls of the mold is called by ceramists “suction of the shard.”
Immediately after pouring the slip, this process goes very quickly, then slows down and stops completely. It is at this point that the slip must be drained (35.2). On the walls of the internal surfaces of the plaster mold there remains a layer of clay in a dough-like state - the walls of the future vessel. After some time, the layer of clay on the walls of the mold begins to dry out (35.3). At the same time, it shrinks. In this case, the casting decreases in size, and its walls (shard) are gradually separated from the plaster mold. At this point, the walls harden and become thinner. After making sure that the casting has dried sufficiently well and its walls have separated from the mold, carefully remove the upper half and, just as slowly, remove the casting from the lower half of the mold (35.4).
While the product is not yet completely dry, it is set: they cut off the prominent seams formed here and there at the joints of the plaster mold with a knife; seal all kinds of dents, depressions and scratches with soft clay; After this, the surface is smoothed with a moistened sponge. If the product is dry, the unevenness can be eliminated using sandpaper. After setting, the product is placed on a shelf and dried at room temperature for five to six days. After drying, the hygroscopicity (moisture absorption) of the gypsum mold is completely restored and the next ceramic product can be cast in it, which will be an exact copy of the first. About two hundred castings can be made in one mold. Of course, a vessel based on a body of rotation can be made in another way, for example, on a potter's wheel. But there are vessels for which casting is almost the only method of molding. These include the rectangular decorative vase shown in the figure (Fig. 36).
The vase model is made from a rectangular wooden block, to which legs and necks turned on a lathe are glued (36.1). A relief is cut out on one or two walls of the model. The finished model is cleaned with sandpaper and impregnated with hot drying oil two or three times. The form according to this model is cast in the same sequence as a round vase, only instead of a cylindrical formwork, a rectangular one assembled from four planks is used (36.2). The formwork and pallet are lubricated with release mastic and liquid gypsum is poured into it so that exactly half of the model is in it. The locking connection is obtained by cutting out conical recesses (36.3a) in the lower half of the mold at the corners, which are lubricated with mastic. After pouring the second half of the mold (36.4), the plaster fills these depressions, forming spikes. When assembling the mold, the tenons will accurately fit into the corresponding recesses and ensure the accuracy of the connection of both halves.
The finished mold is freed from the model, dried, and then casting is performed in a well-known manner (36.5).
The “Skillful Hands” circle from time to time sums up the work done, demonstrating its products at school pioneer exhibitions. Clay products are also exhibited at the exhibition. The best stucco works should be presented for exhibition in plaster, that is, in a more durable, long-lasting material.
Modeled products made from clay, plasticine, and wax have a number of disadvantages. For example, when clay dries, it cracks, falls off, and decreases in volume. Plasticine and wax soften at elevated temperatures, melt and change their shape. Therefore, a sculpture made of clay, plasticine, or wax should be cast from another, more durable material - plaster or cement. To do this, first of all, you should make a rough form.
In the case when the sculpted thing - the original - must be made in several copies, a special adhesive or piece form should be made. This form will help us cast the required number of models. We will talk about the simplest production of rough molds, casting molded products from them, as well as about the materials that are used in molding work.
Gypsum- finely ground white powder - is the most common material for casting sculpted products. Gypsum is obtained from gypsum stone, which is fired at a temperature of no more than 150 degrees. Gypsum is divided into medical, molding and plaster. Medical gypsum is the purest, finely ground and quick-setting. Molding gypsum is almost as pure and finely ground, but with a slower setting time. The beginning of setting is after 4 minutes, and the end of setting is no later than 20 minutes. Plaster gypsum has a coarser grind.
What is the beginning and end of grasping? To prepare a gypsum solution (dough), gypsum powder is mixed with water until the thickness of liquid sour cream. The beginning of setting is determined when the gypsum solution begins to thicken, and the end of setting is when the gypsum becomes hard as stone.
After prolonged mixing, the gypsum solution will “rejuvenate”, that is, it will not set, and if it does set, it will form many cracks and crumble under light pressure. Therefore, the gypsum solution must be prepared quickly in 0.5-1.5 minutes in order to use it before setting begins.
Gypsum has valuable properties, but also has disadvantages. Valuable properties include the speed of setting and hardening, as well as the fact that the gypsum solution increases in volume by up to 1 percent when hardening. This gives it the opportunity to better penetrate all shape reliefs. A significant disadvantage of gypsum is its ability to become warm, which negatively affects adhesive forms, which quickly melt. In addition, the plaster warps.
In order to slow down the setting of gypsum, it is dissolved in glue water (3-4 tablespoons of liquid glue are added to a bucket of water), and to reduce warping - in lime milk.
Gypsum products should not be dried in a draft wind, this will reduce warping. The drying temperature should not exceed 60 degrees. At higher temperatures, gypsum begins to decompose, loses strength, and many cracks form on it. Gypsum is stored in a dry place. When stored for a long time, even in a dry place, gypsum absorbs moisture from the air and stops setting.
Soaked plaster is not suitable for work, as it does not set. It should be noted that gypsum products are stored in dry places; They are destroyed by dampness and water.
Molding plaster is sold in building materials stores, and medical plaster is sold in pharmacies.
Preparation of gypsum solution. The gypsum solution is prepared as follows: pour water into a bowl and gradually add gypsum, mixing it thoroughly. If you first pour gypsum into a bowl and then add water, lumps will form in the solution. To prepare small portions of the solution, gypsum is diluted in rubber plaster cups, wooden or metal ladles.
As we have already said, gypsum should be stirred quickly, for no more than 0.5-1.5 minutes. Gypsum sets faster if it is mixed in warm water.
For work, a colored plaster solution, called a colored splash, is sometimes necessary. In these cases, two tablespoons of some kind of paint are placed on a bucket of water: ocher, mummies, blue. Adding more paint is not recommended as this will reduce the strength of the plaster.
In addition to gypsum, cement can be used for casting products.
Cement- finely ground gray-green powder. It is used for casting products and making lump cement molds. Cement is obtained from stone - marl - or an artificial mixture, which is fired at a temperature of 1400 degrees. After firing, the mixture is ground.
The strength of cement is very high. Cement tiles, after complete drying, can withstand compression from 200 to 600 kilograms per 1 square centimeter.
The beginning of setting of cement is 30 minutes, the end of setting is 12 hours.
A product cast from cement should be kept in the mold for at least 5-7 days, and only after that the mold can be broken. Store cement in a dry place. In addition to the usual grey-green cement, there are colored cements: white, red, blue, green, yellow, etc.
Cement is also sold in building supply stores.
Preparation of cement mortar. For the manufacture of cement products, it is recommended to use cement mortar. For one part of cement, take two or three parts of sand and mix them thoroughly until a homogeneous mixture is obtained. Then the mixture is mixed with water until the consistency of sour cream.
Preparation of glue. To make adhesive forms, bone and flesh glue is used in the form of tiles or cereals. Liquid glue, the so-called galerta, is not suitable for making molds. Glue is sold in building materials stores. The glue should be stored in a dry place, as it rots from dampness.
To make adhesive forms, the adhesive mass is boiled. Before cooking, glue tiles are split into pieces, placed in a bucket and filled with cold (preferably boiled) water. The glue should lie in water for 6 to 12 hours until it swells and becomes soft and elastic. The swollen glue is removed from the water and placed on plywood or burlap for 15-30 minutes to allow excess water to drain off. Then the glue is boiled in a metal container, but not directly over a fire, but in a so-called water bath, that is, in a glass bottle, which consists of two vessels inserted into one another.
During the cooking process, the glue is thoroughly mixed, breaking up the resulting lumps. It is not recommended to bring the glue to a boil, because it loses its adhesive properties. If after cooking the glue turns out to be excessively thick, it is diluted with hot water, but no more than one glass of water per bucket of glue. To prevent the glue from rotting in the summer and eliminate the smell, add 5-10 drops of vinegar essence to a bucket of glue mass.
Before use, the welded glue is cooled to 50-60 degrees so that it does not melt and wash away the lubricant applied to the model, and also does not stick to the model. Then the adhesive mass, having removed the film previously formed on the surface, is poured into the mold.
After use, adhesive forms are re-melted. If the glue thickens during repeated melting, it is diluted with water, and to maintain elasticity, glycerin is added to it, based on two glasses of glycerin per bucket of water.
Alum are used in the form of a solution for tanning adhesive molds, since more products can be cast from a tanned mold than from an untanned one. Aluminum or potassium alum is sold in pharmacies or chemical stores.
A solution of alum is prepared as follows: pour 1 liter of hot water into an iron or enamel bowl and add 300-400 grams of alum. The dishes are kept on the fire until the alum dissolves and the solution boils. The resulting solution is cooled before use, otherwise the hot alum may melt the adhesive form.
Talc- a thin, greasy-to-the-touch powder obtained from grinding soapstone. It is used as a powder for degreasing adhesive molds before tanning them. Sold in pharmacies or chemical supply stores.
Kerosene, soap, oil and stearin used for the preparation of lubricants. Lubricants are necessary to lubricate molds when casting products or to lubricate models before removing molds from them. Lubricant prevents materials from sticking together and thus facilitates their easy separation.
Lubricants can be prepared from different materials according to different recipes. Here are two of the simplest recipes for preparing lubricants.
Recipe 1. 1 kilogram of stearin melts with continuous stirring until it begins to bubble, that is, boil. After this, remove the container with melted stearin from the heat and, stirring thoroughly, pour 2-2.5 liters of kerosene into it. The mixture is then allowed to cool.
Recipe 2. 1 liter of kerosene is mixed with a liter of liquid machine (gar) oil. The resulting mixture is poured into 1 kilogram of stearin previously melted and removed from the heat and mixed. After cooling, the lubricant is ready for use.
Vaseline, vegetable oil, soap suds and sunflower oil are sometimes used to lubricate adhesive forms. The oil is applied in a thin layer, without covering the small pattern on the form.
Drying oil and varnishes. To make models and plaster molds waterproof and smooth, they are coated with drying oil or varnish.
Knowing the basic materials for molding and casting products, you need to become familiar with the tools and fixtures.
Tools and equipment for molding work
For sculpting and molding work, a novice sculptor needs to have some more tools.
Molding blades to prepare gypsum or cement mortar, you need to have both large and small ones; They are not difficult to make yourself.
Chisels large and small, straight and semicircular, which are used for leveling plaster planes, cutting straight lines and clearing cast products.
Semicircular chisels are used for processing cast gypsum products with curved surfaces.
Cycles- for leveling surfaces of cast gypsum tiles or primer products. A cycle is a metal plate 1-1.5 millimeters thick, 50-70 millimeters wide and 100-150 millimeters long. One side of the cycle is smooth, the other has small teeth.
Pliers, chisel, hammer, saw, scissors used for molding work.
Plaster casts are indispensable utensils for preparing various, and in particular gypsum, solutions. They are convenient because the hardened gypsum solution can be easily removed from them with a light blow. Plaster casts do not wrinkle or chip like other dishes. They resemble plaster cups made of black rubber and are sold in pharmacies and surgical supply stores.
If it is impossible to purchase plaster, then it can be made from a ball of any size, cutting it in half.
How to take a hand impression
The simplest form can be made from your own hand or foot or from the hand of a friend. You can use clay for this. When done well, a mold made of clay can produce a good casting, which is necessary not only as a model for modeling, but also as a visual aid when going through anatomy.
Before removing the mold, you need to prepare at least half a bucket of soft clay. Then take a sheet of plywood or a planed board, that is, a stand, and grease it with a thin layer of vegetable oil, Vaseline or lard. You should also grease the hand from which the form will be removed, but not very greasy. Then the hand is pressed with the palm of the hand onto the plywood or board. The fingers of the hand, depending on desire, can be closed or spread apart.
A thin layer (1 cm) of clay is applied to the hand and pressed firmly onto the hand. Then a second layer of clay is placed on the hand, and it is also pressed tightly. Having thus placed 2-3 layers of clay on your hand with a total thickness of 6-7 centimeters, the top of the clay is leveled and a lining, board or plywood is placed on it, supporting it. Then the hand with the clay placed on it is turned over so that the lining is at the bottom. Next, the stand that is at the top is removed from the hand, and the hand is carefully removed from the clay. The mold for casting one hand cast is ready.
The quality of the mold made depends on the care of laying and the thickness of the layer of applied clay. The thicker the layer of clay, the better and stronger the shape. The thin walls of the mold do not have sufficient rigidity; they expand from the weight of the poured gypsum solution, and the cast cast is distorted.
Before casting, the mold should be well moistened with water, spraying it from the mouth or a spray bottle. When the mold is ready, prepare a gypsum solution (the solution should be no thicker than sour cream) so that it can be completely filled with the mold. The plaster should be poured gradually, starting from the highest part of the mold, from where it will drain and fill the entire mold, displacing the air present in the recesses. After 30-40 minutes, the plaster will have set so much that the clay can be carefully removed from it. The castings should then be thoroughly cleaned and any defects corrected.
A cast of the hand can be made from cement.
Now let's get acquainted with the production of rough forms.
Making rough molds
Rough forms are removed exclusively from things fashioned from soft plastic materials: clay, plasticine or wax. Rough molds are rarely removed entirely from the cast plaster model; Most often, the mold is split into small pieces, which is how the cast model is released.
Depending on the complexity of the model, the form may consist of one, two or more parts. All forms are removed in the same way as we will now analyze using two examples.
Making a rough form from relief flat models. A rough mold from flat models is made in the following order. The clay model intended for rough molding is well moistened with water. (Models made from plasticine and wax do not undergo any preparation before molding.) Then a plaster colored splash is diluted, a layer no thicker than 5 mm is splashed over the model and castles in the form of mushrooms are arranged on the splash. As soon as the splash has set, a supporting layer of white gypsum mortar is applied. After the gypsum solution has set, after about 40-60 minutes, the prepared form is slightly separated from the board using a wedge, thereby forming a small gap. Water is poured into the gap in excess. Water soaks the clay, and the mold is easily removed. If the mold is made from a soft clay model, it can be easily removed without wetting the clay with water.
The removed form is examined and the remaining pieces of clay are selected from it using a wooden tool or knife; after which the mold is washed well with water, freeing it from possible tiny particles of clay that clog the sharpness of the drawing. It is better to wash the mold with water using a syringe. It is not recommended to leave a clay model in a rough form for a long time, since dried clay is difficult to remove and wash out of the mold. The removed rough mold, after removing the clay from it, should be quickly used to cast a product from it. Long-term storage causes the mold to dry out and warp, producing distorted castings. This is how the mold is removed from flat models.
Making a rough form from three-dimensional models. A molded model, for example a jug, is well moistened with water until completely saturated. It is possible to remove the entire mold from the jug, but it is not possible to select clay from it. Therefore, the mold must be made of two halves.
The model is divided into two parts using a special side. The side is formed from plates of thin tin or foil. The dimensions of the plates should be no longer than 60 millimeters and no wider than 40 millimeters. The plates are inserted into the model to a depth of 10-15 millimeters so that they fit tightly to each other. It is best to insert them in such a way that each inserted plate overlaps the previous ones by 2-3 millimeters.
Having inserted the plates and lubricated them with grease, they begin to make the first half of the mold. The remaining second part of the model is covered with a wet rag or paper, protecting it from drops of gypsum solution. Then a gypsum colored splash is prepared. It is beveled onto the model from below, gradually moving upward. Mushroom locks are made on the splash. After the gypsum solution has set, they begin to apply a supporting layer - a thicker layer of white gypsum solution.
After the supporting layer has been applied and set and the gypsum has completely set, the plates are removed and made on the edges of the first half of the mold, holes, that is, small, 5-10 millimeters, recesses, drilling them with a molding spatula or knife.
The holes are made in order to form bulges on the second half of the mold. In general it is called lock. The lock ensures an accurate connection of the halves to each other and does not allow them to move during casting of the model.
The edges of the mold with drilled holes are lubricated with grease. Remove the rag or paper from the model, remove any trapped plaster crumbs and begin constructing the second half of the mold.
The second half of the form is arranged in exactly the same way as the first. First, a colored splash is applied to the model, and mushroom locks are arranged on it. A supporting layer is applied to the splash. As soon as the gypsum solution has hardened, begin to separate the halves of the mold.
Wedges are inserted into the seams between the halves of the mold, slightly they are driven in, thereby separating the halves.
A small amount of water is poured into the holes formed between the mold halves and the clay model. Water soaks the clay, and the mold halves are easily removed from the model.
The prepared mold is well cleaned of all pieces of clay, well saturated with water, bound and casted.
The casting should not be made massive, but so-called hollow - hollow. The hollow model is lighter and uses less material. For casting, prepare a small amount of gypsum solution, pour it into a mold tightly tied with ropes and begin to turn the mold in all directions, but so that the gypsum solution does not spill out of the hole. Thus, the gypsum solution rolled over, that is, the cover, in a thin layer over the entire form. After the first rolling, the second and third are performed. After rolling the mold three times, a gypsum wall 2-5 centimeters thick is formed, which depends on the size of the model.
Casting a model from rough molds
There are two ways to prepare rough molds before casting models from them.
First way consists in the fact that the removed form is well saturated with water, that is, it is placed in water for 20-30 minutes. Then the inside of the mold taken out of the water is moistened with soapy water so that no bubbles remain on the mold, and the prepared gypsum solution is poured into the mold.
Second way preparing the form is not very common, but is more suitable for beginners. The prepared mold is dried for 2-3 hours, then covered with alcohol varnish, after it has dried, lubricated with lubricant and a gypsum solution is poured into it.
The second method is quite tested and has proven itself well.
The gypsum solution is poured into the mold to its highest point. This is done so that the solution flows evenly and fills all the recesses, while simultaneously displacing air from them.
If you pour a large amount of gypsum mortar into the mold at once, it can delay the release of air from various recesses of the mold. In this case, air pockets are formed that prevent the mold from being filled with gypsum mortar, and the cast model will be defective.
When the mold is closed, consisting of two halves, such as the mold of a vase, then both halves are greased with grease, joined together, tied tightly with rope in two or three places, and first a small amount of gypsum mortar is poured into the mold. The mold is turned in all directions so that the poured plaster can cover the entire mold with a thin layer. After the first rolling, a second portion of gypsum solution is prepared, poured into the mold and rolled again. In this way, layers of gypsum are gradually built up, bringing its thickness to 2-5 centimeters.
Splitting the mold
After two hours, when the gypsum solution has hardened in the mold, they begin to excavate the model. Since the model is not always removed from the mold, the mold very often has to be cracked, that is, broken into small pieces. Splitting is carried out in different ways. In one case, chipping the mold material is done using a chisel, chisel and hammer; in another case, the mold material is pierced with a thick knife. In both cases, care must be taken not to damage the cast model. This is well facilitated by a colored splash, which warns that there is a model within 5 millimeters.
When the mold is prepared using the second method, splitting is very easy. If the mold is removed from small items, then before chopping, the surface of the mold should be divided into small parts - pieces, no more than one centimeter, by cutting strips, grooves along their edges with a knife or other tool. The splash should also be slightly cut and removed in separate pieces.
After splitting, the freed model is corrected. If the plaster is not white enough, wipe the model with fine chalk or tooth powder.
Model clearing
Models cast from rough molds have some defects: roughness, insufficiently pronounced wrinkles, folds, lines, small cavities (depressions) that require correction or, as they say, cleaning.
First of all, small shells are covered with prepared gypsum mortar. Then, using a metal stack or knife, they begin to clear the model. Rough areas are smoothed with sandpaper or glass sandpaper. After drying the product, you can rub it with tooth powder using a brush to make it whiter.
Now let's get acquainted with the manufacture of adhesive forms.
Making adhesive forms
It is rarely possible to obtain several products from a rough mold, since it usually breaks during the first casting.
In the case when it is necessary to cast several products, an adhesive mold is made. Let us examine in more detail the production of adhesive forms from different models.
Glue forms are made in different ways and only from rigid models made of stone, metal and most often plaster.
In order to make the surfaces of plaster models smoother and close the pores on them, they are coated once or twice with alcohol varnish before molding.
Making adhesive molds using the open method. We need to make an adhesive mold from a flat model, for example from a sheet whose maximum height is 30 millimeters. First, a gypsum board is made of such a size that it is 50-70 millimeters larger in width and length than the model. The model is fixed on a gypsum board, the cracks are smeared with plaster or clay and covered with alcohol varnish. At a distance of 1.5-2 centimeters from the model, a barrier is arranged - a side made of wooden planks, clay, plaster, tin. Its height is 40-45 millimeters, that is, 10-15 millimeters higher than the highest part of the model. To prevent the glue from leaking under the barrier, the places where it adjoins the gypsum slab, that is, the seams, are coated on the outside with clay and plaster, and on the inside, the model, barrier and slab are lubricated with lubricant. If the model has an openwork pattern, then remove excess lubricant from it with a soft brush.
Then the model is filled to the edges of the barrier or slightly below with the prepared adhesive mass, cooled to 50-60 degrees. Higher adhesive temperatures are not advisable as they will wash away the lubricant. After the glue hardens, after 18-20 hours, the barrier is removed, the adhesive mold is released from the model and the casting of products begins, after lubricating the mold with lubricant.
When casting products, the mold must be placed on a smooth and even surface. If there is any debris under the mold, the mold will bend and the casting will be crooked. To protect the adhesive mold from deflections and distortions during casting, it is best to place it in a casing - a box, usually made of plaster. The casing is made as follows: the sharp edges of the mold are cut off from the outside with a knife and several small holes-holes 0.5 millimeters deep and 10-20 millimeters wide are cut out on its plane. The pits serve to form locks on the casing. Locks are subsequently necessary for the correct installation of forms in the casing. Then they put a mold on the model, lubricate the surface and edges of the slab, spread the plaster and coat the mold with it to a layer thickness of 10 millimeters.
To give the casing greater strength, thin shingles, wire or tow soaked in diluted gypsum are placed in the unset plaster and the casing is coated a second time with diluted gypsum. The plaster is leveled, creating a casing thickness of 20-30 millimeters. After the plaster has set, the casing is removed from the adhesive mold, and the adhesive mold is removed from the model.
The manufactured mold is suitable for casting products, but it can quickly collapse. To protect the adhesive form from destruction, it is tanned. To do this, sprinkle the front working side of the mold with talc, lightly wipe the entire working side with a dry soft brush, remove excess talc and wash with a brush with a cooled alum solution. The alum solution accumulated in the recess is selected using a dry brush or cotton wool.
The tanned mold is dried for about an hour and impregnated with alum a second time. After the second impregnation, it is dried for about 5-6 hours with light ventilation. It must be remembered that without powdering with talcum powder, alum will not be absorbed into the greasy surface of the mold. Talc degreases the mold.
The casing must also be prepared, that is, dried and coated well with alcohol varnish (it is better to dry it first and then varnish it). The adhesive form should only be in a dry casing. This is necessary because when it comes into contact with the wet surface of the casing, it swells, increases in volume, changes its original shape and thereby distorts the casting. To make it easier to remove the mold from the casing, it is also recommended to sprinkle the inner surface of the casing with talcum powder.
In this way, adhesive molds are made from flat models. It is impossible to make molds from tall models in the same way as from flat models. The walls of such forms will be very thick and will require a lot of glue. Therefore, they must be produced in a closed way.
Making adhesive molds using a closed method. The production of adhesive molds from tall models is done in a different way. If you make the mold as indicated above, then in some places the layer of glue will be very thick. The thick form is not elastic and not economical. When casting a thick mold, damage may occur to the insufficiently strengthened material (product) and even to the model with which it is made. In this regard, the adhesive form should be no thinner than 5 millimeters and no thicker than 25 millimeters; it should be thin, bend freely and not spoil the molded products.
For example, you need to make a mold from an apple. To make this shape, a gypsum board is made so that it is 50-70 millimeters larger than the base of the apple on all sides. The model is installed on the slab and fastened well to it. Then everything is coated with alcohol varnish. After this, the model is wrapped in a single layer of newsprint to protect it from contamination by clay. Next, they take soft clay, give it the shape of a cube or brick and cut it with a thread into plates 15-25 millimeters thick, which depends on the size of the model. For a small model - 15 millimeters, for a large one - 25 millimeters. The model is covered with cut clay plates. At the same time, make sure that the clay is well smoothed.
Then, holes are drilled around the model on the slab in different places at a distance of 5 millimeters from the clay to install locks. The locks prevent the casing from moving from the model when pouring glue and at the same time serve as marks indicating the location of the casing during its assembly. The holes are cleaned of gypsum shavings, then the edges of the slab with the selected holes are lubricated with grease.
Since it is impossible to remove the entire casing from such a model, it is made detachable, consisting of two halves, for which plates are inserted into the clay, and thus the model is divided into two equal parts. The clay is then moistened with water. Then the plates are lubricated with lubricant and the gypsum solution is diluted. The gypsum solution is spread on one half of the model, making the first half of the casing. Both the first and second half must be well reinforced with hemp, wire, and tow.
As soon as the plaster has set, the plates are removed, the edges of the first half of the casing are well aligned, holes are made on them, lubricated with grease and the second half of the casing is made. The thickness of the casing varies. For medium-sized models, it should not exceed 3 centimeters. Thicker casings are uneconomical, require a lot of material and are heavy. It is best to make thin casings, reinforcing them well. 30-60 minutes after making the second half, the casing is removed from the clay, and the clay and paper are removed from the model. If you now cover the model with a casing, then a space will be formed between the model and the inside of the casing, resulting from the removed layer of clay. Liquid glue is poured into the resulting space, which hardens to form an adhesive form. To do this, a hole with a diameter of 40-60 millimeters is drilled at the top of the casing in its middle for pouring glue. Along the edges of the casing above the highest parts of the model, several holes of a smaller diameter are drilled - 5-10 millimeters. They are designed to allow air to escape from the casing when glue is poured into it. If this is not done, air accumulated under the casing will prevent the glue from filling the model and the mold will deteriorate. In addition, when the glue hardens, it increases in volume (expands), its excess comes out through these holes, subsequently forming locks.
The holes are drilled onto a cone so that they are wider on the inside and narrower on the outside. This makes it easy to remove the casing from the cured adhesive. To fill large models with glue, it is recommended to drill not one, but two holes in different places. The glue is poured through these holes at the same time.
If you pour glue into one hole, then, while passing through a large space, it will cool along the way and will not flood the entire model, and this will lead to defects. It is recommended to drill holes over smooth areas of the model. This is necessary because when pouring glue, the lubricant is often washed off, the glue sticks to the model and spoils its relief. It is easier to repair damage in a smooth area than in areas with a relief pattern.
Having drilled all the holes in the casing, its inner side is coated twice with alcohol varnish; The edge model of the plate and the inside of the casing are well lubricated with grease. The casing is additionally sprinkled with talcum powder and the model is covered with it so that the locks fall into place. To prevent the glue from leaking out of the seams when pouring, the joints between the casing and the slab are coated with clay or plaster. The slab is tied to the casing with ropes or some heavy weight is placed on the casing. This is done so that the glue, expanding, does not lift the casing when it sets, but, on the contrary, puts pressure on the model, goes into all the relief places, thereby forming a clearer pattern on the form. Molten glue is poured into the casing using a funnel with a volume of at least 0.5 liters, which is made from roofing iron, cardboard or clay. The funnel is installed on the casing, and the connection point on the outside is coated with clay or plaster. The inside of the funnel is lubricated with grease and glue is poured.
The glue is poured through a funnel, thereby filling the empty space between the model and the casing. In cases where glue begins to leak through the air holes, they are covered with clay. Fill the funnel completely with glue. A high level of glue in the funnel increases the glue pressure in the mold, and there will be no bubbles or cavities on its surface, which reduce the quality of the mold. After the glue has hardened, the casing is removed from the glue mold, and the mold is removed from the model.
Since it is impossible to remove the mold from the model as a whole, it is cut into two parts using a sharp knife. It is advisable to cut along the seam of the casing. Then the adhesive mold is degreased, tanned, dried, the casing is varnished - and it is ready for casting products from it.
A mold made using a closed method is more durable because the glue becomes denser and the pattern on it is formed more sharply.
Using this method, you can make a mold from any three-dimensional model. In the case when the model is complex, the form has to be cut not into two, but into three or more parts. The casing is most often made of two parts.
Thus, we became acquainted with the production of adhesive forms from flat and volumetric models. But what to do when there is no glue, but you need to multiply, that is, cast several castings from a plaster model sculpted and cast from a rough mold? It turns out that, in addition to the adhesive form, there is a so-called piece, or plaster, form. Thus, when there is no glue, but there is plaster, a plaster mold can be made.
It is necessary to point out that making a gypsum mold is much more difficult than an adhesive one, since a gypsum, or piece, mold rarely consists of one or two pieces. Most often it consists of several pieces.
We will analyze the production of piece molds using the simplest models. It is necessary to point out that piece molds are made only from durable models made of plaster, stone, wood, and metal. Plaster and wooden models must be fixed, that is, coated twice with alcohol varnish.
In this case, we will talk about making the simplest piece molds. For example, we have a model of an apple. From this model, a piece mold should be made for casting several products.
The simplest form can consist of two pieces: first and second, or lower and upper. Before you begin making the mold, the model should be prepared.
The plaster model is first coated once or twice with alcohol varnish and, after the varnish has dried, lubricated with lubricant.
Before molding, the model should be divided in height into two parts so that the halves of the molds can be easily removed from them. If the halves jam, it will be impossible to remove the castings from them without ruining the molds. Then the model must be placed in sand or sprinkled with wet sand so that only one half of the model, intended for molding, protrudes from it.
Manufacturing of lump molds
After this, the gypsum solution is diluted and a thin layer is splashed over the model. A second layer is applied to the first layer of gypsum that has not set, smoothing it well. The thickness of the plaster layers or mold walls should be 20-25 millimeters.
As soon as the applied plaster sets, and this will happen in 40-60 minutes, the model is removed from the mold, the edges of the mold are aligned, that is, they are cut with a knife and two or three holes are drilled on them. The holes are needed so that another piece can form locks in them.
Then the piece is well swept to remove plaster crumbs using a brush, the model is placed in the mold, the edges of the mold and the model are lubricated with grease, and the second piece is started to be laid or made. The second piece is laid in the same way as the first: that is, a gypsum solution is prepared, applied to the model in a thin layer, and a second layer of gypsum is applied to the thin layer. As soon as the plaster has set well, the entire outer surface of the mold is cut off and the pieces are separated. The manufactured mold is suitable for casting hollow products.
Before casting, the inside of the two pieces of the mold is lubricated with lubricant. Then a portion of gypsum mortar is prepared. Fill only one half of the mold with plaster and cover it with the other half, turning it in different directions. The solution flows over the entire mold, covering its walls with a 15-20 mm layer of gypsum mortar.
As soon as the plaster sets, the mold is separated and the cast product is removed. For strength, the mold should be dried after casting and coated two or three times with alcohol varnish.
Casting of products from molds is carried out as described above. When casting gypsum products in adhesive molds, the castings should be removed from the mold no later than 25-30 minutes after filling the mold with plaster. Cement products cannot be cast in adhesive molds, but only in lumps. The castings need to be kept for 3-5 days.
Manufacturing of various tools and devices
As we have already said, various tools and devices are needed for sculpting. Some tools and devices can easily be made by the members of the Skillful Hands circle themselves, such as stacks, stands, easels, etc.
Stacks. Wooden stacks are cut from dry wood using a sharp knife or chisel. After processing the stack with a knife, it is cleaned with sandpaper or a piece of glass. For strength, it is good to soak the stack with drying oil or any vegetable oil, allowing it to dry after this for 2-3 days.
For cutting off excess clay and cutting out recessed areas, use stacks with metal tips. Wooden cuttings are made. Then they take 2-3 mm copper or iron wire, cut it into pieces 10-15 centimeters long and give it the desired shape. Hooks are bent at the ends of the wire. Then grooves are cut on each side of the wooden handle, and holes are pierced at the bottom with an awl or nail. Wire hooks are inserted into these holes and twisted with thin wire. The tips are flattened using a hammer. At the ends of some tips, teeth are sawn through with a file. With their help, dried clay is cut off better.
It is better to make three to five stacks, of different sizes and shapes.
Used for modeling and metal stacks, which can be made from copper, aluminum or iron wire using a hammer and file.
Metal compass You can buy it in a store, but you can easily make a wooden one yourself. Typically, a compass consists of two legs with sharp ends connected by a screw. Making a compass does not seem particularly difficult. They take plywood 5 millimeters thick, from which they cut out planks, or better yet, plan two planks 1 centimeter thick, 2-2.5 centimeters wide, 25-30 centimeters long, and give them the shape of a needle, that is, wider at the top, and downstairs already. The planks are folded together, a hole is drilled at the top into which a wing screw or thin bolt and nut is inserted. If there are no such screws, the planks can simply be connected with an ordinary screw, which is tightened when the legs are loosened. At the lower ends of the legs, thin nails should be inserted or iron tips from roofing iron and tin should be nailed; in the figure (Fig. 248 (5) The device of the compass is shown.
Pantograph compasses come in metal and wood; Both are sold in stores but can be easily made. We told you how to make a pantograph compass yourself on pages 132-134.
Mernik It is made as follows: four strips 10 centimeters long and 2-3 centimeters wide are cut out of tin or roofing iron. Brackets are made from two strips of such a size that they can cover the guide. The brackets are nailed to two legs and a guide is put on them, along which they should move freely. Then they take a piece of wood with a cross-section of 2-3 centimeters and a length of 5 centimeters, necessary for the manufacture of the engine. A groove with a cross-section of 2-3 centimeters is cut out on the engine, that is, such a size that the pin can freely fit into it. The engine is nailed with brackets to the guide and a ruler is inserted into the hole. Having assembled the measuring stick, that is, putting on the legs and pin, we can assume that it is ready for measurement. The legs and pin move along a guide and have to be installed motionless in the right places. To secure them in one place, you need to screw in thin screws. The engine is secured with two screws. One is the engine itself, and the other is a pin that can be extended and lowered to any height (Fig. 256).
Brushes You can buy it, or you can make it yourself from horsehair or bristles. They are made like this: take a tuft of hair or bristles, align their ends and tie them on one side in one or two places with strong twine, after which one end is cut off, make a wooden handle with one pointed end and place the tied tuft of hair on it or secure it in a metal frame.
Douche made like this. Take a piece of metal tube 30-40 centimeters long, with an internal diameter of 2 to 4 centimeters. The rusty inside of the tube must be cleaned by wrapping a rag on a stick, moistening it with water, and sprinkling it with emery powder or finely crushed and sifted bricks. Insert it and move it along the tube. Having cleaned the tube, one end of it is filled with lead 2-3 centimeters thick or plugged with a wooden stopper, in which a hole of 1-2 millimeters is drilled. Then they make a piston, that is, they take a wooden or iron rod with a diameter of 6 to 12 millimeters (the wooden one is thicker). The length of the piston is 5-10 centimeters greater than the diameter of the tube. At one end it is secured with a wooden sleeve with a diameter 5-6 millimeters smaller than the inner diameter of the tube. The muff is wrapped with flax or a rag, but so that it fits tightly into the tube. The winding is lubricated with machine oil, grease or Vaseline. A handle is made at the other end of the rod, and the syringe is considered ready. To ensure smooth movement of the piston, it is advisable to insert a second plug at the second end, making a hole in it along the diameter of the rod.
There are traditional techniques for working with clay. There are only six of them:
1) tape-bundle - popular in the northwestern regions of Russia and Tajikistan;
2) East Siberian modeling of vessels from several parts with joints running in a vertical direction;
3) Central Asian sculpture of vessels from four horizontal belts;
4) molding by knocking out;
5) kneading into the finished form:
6) last on the list, but not least - drawing a vessel from one piece of clay on a potter's wheel. There is, however, one more method of making clay vessels, but it can hardly be distinguished as a separate, seventh, method, since with its help only very monotonous vessels for wine and grain were made in the Neolithic era.
In this way, the vessels were “erected” by hand, like building structures. A form was sewn from coarse fabric according to the outlines of the future vessel, which was filled with sand. The outside of the mold filled with sand was coated with clay. As the vessel dried, the sand was gradually poured out of the bag, and the vessel was burned in the fire. An imprint of the fabric - the former shell of the form - was sometimes left on the inside of the vessel.
Separately, it should be said about the casting method, when the slip is poured into a plaster mold. Today it is the most common method of producing ceramic products, including majolica, earthenware and porcelain. It appeared in the Middle Ages and, thanks to its technological simplicity, quickly began to supplant all other methods of making ceramics. But the ancient traditional ways of working with clay have not completely disappeared in our time. With their help, highly artistic ceramic works are created that reveal the wonderful properties of clay and at the same time serve people. Therefore, we will tell you more about them.
To work with the first method, you need a tournette (a round table made of metal, plastic or wood rotating on an axis) or a similar object that replaces it. You need to stick a flat cake rolled out with a rolling pin onto the rotating surface. Having cut off the excess, leave an even clay circle on it and begin to wind the wall of the future vessel from clay strands along its edge. This process is similar to the process of weaving a basket, but only without vertical rods, since the strands, unlike the vine, are stuck together, and as the wall of the vessel grows, they are leveled with fingers or a stack.
The second method of making pottery is simpler to describe, but more difficult to use. Having rolled out the clay, like dough, into a 4 mm thick flap, you need to carefully cut out the parts of the future vessel and prepare them for gluing. This process is very similar to patchwork. Clay flaps need to be glued in a dried state (in a hard leather, as ceramists call it). On the surfaces to be glued (seams) you need to apply a notch with a scalpel and lubricate it with slip, like glue. This method of working with clay has recently become widespread. Ceramists, in the literal sense of the word, “sew” all kinds of products from clay, ranging from the simplest household items to complex sculptural compositions. By placing various textured fabrics on the table when rolling clay, you can get clay rags with the desired pattern. Nowadays this method of clay “sewing” is called textile ceramics.
The third method of making clay products differs from the second only in the direction of the seams of the elements being glued together.
Fourth method working with clay, but it is the most difficult, and now I have great difficulty believing that our ancestors made rather thin-walled vessels in this way. (But it’s hard to believe that people, by rubbing a wooden stick resting against a log in their palms, made fire.) To make a vessel using the knocking method, you take a piece of clay, press a rolling pin into it, but not all the way through, but leaving a layer, which will serve as the bottom of the future vessel. Then place the rolling pin together with the clay horizontally and begin to expand the hole in the clay, as if rolling it out from the inside. When the wall of the vessel begins to sag under its own weight, place the vessel on the bottom and, hitting the rolling pin from the inside (while placing a specially rounded board or palm on the outside), bring the thickness of the vessel wall to the desired level - 5-6 mm. Then attach a pre-made neck to the cylinder or pot obtained in this way. The bottle or jar is ready.
The fifth method - kneading into a finished form - involves repeating previously prepared forms with clay. The mold is made from almost any material: wood, metal, plaster; it can be either solid or composite. When making solid molds, it must be taken into account that the clay products pressed into them must be freely removed.
These methods of processing clay were used in the manufacture of a wide variety of household items until an unknown genius, who can only be compared with the inventor of the wheel, created the potter's wheel. And only on it was clay able to show everything that it is capable of.
At first people worked for. a hand potter's wheel, which greatly limited their capabilities, since they worked with one hand while the other rotated the wheel. With the invention of the foot circle and the release of the second hand, man was able to finally liberate clay.
The foot circle, which was used by old Russian masters, was made of wood (with the exception of a metal rod that served as a bearing) and consisted of two disks: the upper one 40 cm in diameter and 5 cm thick and the lower one 60 cm in diameter and also 5 cm thick. The disks were strengthened horizontally, parallel to each other at a distance of 40-45 cm, with six or eight bars placed either completely vertically or with a slight inclination to the central axis.
The central axis - a wooden round shaft 50 cm long - passed through the lower flywheel circle and was fixed at the lower end (either by driving it into the ground through the workshop floor, or by attaching a “foot” to a thick board nailed tightly to the workshop floor). A metal pin was driven into the upper end, on which, like on a bearing, the wooden spindles fastened together rotated. If the hole in the lower circle became too large for the shaft and the circle “dangled”, the shaft in this place was wrapped with hemp or flax tow. During work, to make the circle move easier, the shaft at the bottom circle was moistened with water, and the upper metal rod was lubricated with vegetable oil.
The modern pottery wheel is equipped with an electric motor. How to work on a pottery wheel? Of course, it is difficult to teach this in words. The main assistant here is again your future experience. But I will still draw your attention to the main points, I will simply share my own experience, which indicates that the potter’s wheel is a full-fledged co-author of the master, since it helps to feel the harmony of form.
To work on a potter's wheel you need certain abilities and certain data. The first thing you need to start with, just like when learning to play the piano, is with the placement of your hands. Remember, if you don't place your hands correctly, you will never achieve good results. You will not be able to feel the thickness of the wall of the vessel, which means it will either come out very thick and heavy, or you will make very thin walls before finishing the vessel. And this simply will not allow you to unscrew it completely - it will collapse. There are three main hand positions when working on a pottery wheel.
The first, which potters use at the beginning of work, twisting the vessel by about one third with this position of the hands. In this position, the wall at the base of the future vessel is located between the middle finger of the left hand and the little finger of the right. The little finger is located horizontally, and the fingers of the left hand are vertical.
The second position is the main one, with it you give the vessel its final shape. The wall of the vessel being pulled out is located between the index fingers, but turned out so that the index finger of the right hand is located horizontally and above the thumb, and you seem to hug the vessel with your entire right palm; The left index finger is positioned vertically and forms a cross with the right.
The third position of the hands is necessary for the potter mainly to form the “lips” of the vessel. The walls of the vessel are located between the pads of the index fingers, while the index finger of the left hand is located below the thumb. When you achieve a certain skill, you may develop your own peculiarities in hand placement, as, indeed, they appear in violinists and pianists, but these characteristics should never distort the basic principle of correct hand placement. It is known that relearning is much more difficult than learning.
After placing your hands, you should master the basic operations. The first is centering the clay on the wheel. At the same time, with the palm of your right hand you need to learn to crush the clay towards the center, forming a cone. The thigh can serve as a support for the elbow of the right hand. Then, pressing the cone with the palm of your left hand, lower it down to the shape of a washer and so on several times until the clay in the shape of a hemisphere rotates smoothly on the circle without any beating. The centering process not only mixes the clay and allows you to move on to the next stage of work, but also allows you to get rid of the remaining small air bubbles that pop out of the clay when forming a cone. When centering, you need to skillfully change the speed of rotation of the circle. As hand pressure increases, the speed should increase. If you do not learn to center the clay correctly, you will never truly master the art of pottery, since even a small beating of poorly centered clay at the beginning of the work will increase as the vessel grows and will eventually tear it off the wheel.
An important point in the work process is fixing the bottom of the vessel. This is where intuition needs to come in and can be helped. To begin with, make ordinary trapezoidal flower pots in a vertical section with a hole in the bottom, which will give you the opportunity to feel its thickness. The thickness of the bottom and walls of a pottery vessel should be 2-4 mm, depending on your skill, the quality of the clay, the size of the product and its purpose or nature. But everything is in order.
Make a hole in the center of a centered piece of clay with your finger, moisten it with water (when working on a pottery wheel, you should constantly wet your hands in a basin of water) and push the clay to an imaginary bottom. Then accelerate the clay using radial forces to the size of the future bottom of the vessel and only after that begin to pull the walls. Make the main effort with the hand that is outside, and with the other you mainly support the clay from the inside. This is, so to speak, the main point. When making various shapes, hands constantly seem to exchange forces. But by no means does any of them completely weaken. You seem to pull the clay up and in, up and out, with the fingers of your right hand slightly lower than the fingers of your left, between them the clay takes the shape of the letter "8". The vessel grows upward and wider under the influence of your hands.
Don’t try to make a vase or jar right away. Practice individual operations first. And don’t be sorry to crush the first clumsy works. There is no need to produce freaks - this is the commandment of the ancient masters. And remember the most important thing: completely trust the clay, its internal memory, do not contradict it under any circumstances, because clay only holds harmonious forms. Do not forget about centrifugal forces, which, in general, form a clay vessel. As the vessel grows, the speed of rotation of the circle, and therefore the centrifugal force, must decrease, otherwise the vessel will simply collapse.
After finishing the work, blot the vessel with a sponge, trim off the excess clay at the base of the vessel with a cutter, let it stand and dry for a while. During this time, you can evaluate your work, and if your intuition tells you that the work was a success, take the string and cut the vessel from the circle. And when you truly master the skill of a potter, then every time you pick up a freshly made vessel, you will be sincerely surprised at its extraordinary lightness relative to its volume. It will seem much lighter to you than the piece of clay from which you unscrew it. And it is this imaginary difference in weight that will always measure your skill.
Next, you should run around with the vessel like a small child, because drying is a very crucial moment in making pottery. If you dry the product incorrectly, you will negate all your previous efforts. Remember: a freshly unscrewed vessel is most afraid of drafts. Therefore, products need to be dried in specially designated areas. Products must dry slowly enough so that there is no tension inside the clay between the thinnest parts that have already dried and shrunk and the still wet ones. That is why it is desirable, and by and large, absolutely necessary, that the thickness of the walls of the product be the same everywhere, and this will depend on your skill.
The most complex products - glued ones, with spouts, handles and various moldings - should dry very slowly and preferably in special drying cabinets or simply under plastic film. But you shouldn’t overdry the product either, since it will again absorb moisture from the air until it reaches equilibrium with the ambient humidity. A characteristic and important moment in the drying process of any clay product is the moment the shrinkage stops. This moment occurs when the evaporation mirror begins to gradually move deeper into the product and its surface begins to brighten. From this point on, the drying speed can be increased. The amount of remaining water after shrinkage stops for plastic clays is about 10-20%, for kaolins - 25-30%. The technical name for this remaining water is "pore water" (as opposed to the "shrinkage water" removed during the shrinkage process). The residual moisture after drying is usually 6-8%.
The more dispersed and plastic the clay, the higher the shrinkage during drying. For example, Prosyanovsky kaolin has a linear shrinkage during drying of -2-3%, loess - 3.5-5.5%, Gomel clay - 6.4%, Cambrian clay, on which the Pokrovskaya Ceramics artel works, - 6.4 -6.6%, Chasov-Yar clays 8-10.5%. And one more thing: the behavior of clay depends on the duration of drying and the thickness of the walls of the vessels. Slow drying causes the clay to shrink slightly more than rapid drying. The volumetric mass of clay and the strength of products decrease slightly during rapid drying, and the thicker the walls of the vessels, the greater the shrinkage. The introduction of an electrolyte (liquid glass or office glue) into the clay or an increase in the amount of ottoshatel reduces shrinkage during drying. Be sure to use the experience of Pechora potters in your work: to prevent the bottoms of small-diameter vessels from cracking during drying, they wrap the bottom of the vessel with a slightly damp rag or newspaper for the first time of drying. To prevent the bottom of a large-diameter dish from cracking during drying, you need to wrap a damp cloth around the edges of the dish.
It is necessary to say something about polishing. This is one of the ancient ways of decorating ceramic products. A shard in a leather-hard state is smoothed with a polish, which is made of stone, bone, wood or metal. The surface of the shard is thus compacted and smoothed to a shine, which is retained even after firing. On the surface of a black-polished vessel, partial polishing creates shiny patterns on a matte black background. Let us emphasize once again that polishing is carried out on a product that is not completely dry. If this moment is missed and the product is dry, then it must be moistened before polishing. This can be done in several ways: by washing it with a damp sponge, spraying it with water from a spray bottle, or very quickly dipping it in water.
After the product is properly dried, you should wash it. This term refers to an operation that requires special care, since you can break the product, because before firing it is very fragile. When washing, you wipe it with a damp sponge, as if wiping off dust, and at the same time all roughness, burrs, and irregularities are washed away with water and disappear.
The products are ready for firing.
When writing this article, material was used from the Encyclopedic Dictionary of Brockhaus and Efron (1890-1907)
Rough molding into plaster
Let's consider the process of "rough" molding into plaster. That is, the technology for creating the simplest plaster mold, followed by casting.
“Roughing” is called molding from a model sculpted in a soft material, with the aim of transferring the model into plaster or another material convenient for subsequent finishing.
In contrast to “finishing” molding, which is usually done from a finished model made of plaster or other hard material, for the purpose of further conversion to other materials, casting of editions (several pieces or more), etc.
Simply put, the sculptor sculpted something in a soft material (clay or plasticine), but in this form the sculpture can neither be stored nor displayed - it is easy to dent, and the clay also dries. Consequently, it is necessary to transfer the sculpture into another material, one in which the sculpture can, firstly, be preserved, and secondly, if necessary, modify it.
The most traditional material for these purposes, dating back to the times of Ancient Egypt, is gypsum.
Of course, you can immediately convert the sculpture into other, more durable materials, especially if there is practically nothing to finish, but the essence of the molding operations will not change.
The area where you will be molding can be covered with plastic film. It is advisable to cover the floor and surface of the sculpting machine, work table, or just a stool on which you are going to mold with the same film. These useful actions will significantly reduce the scale of subsequent cleaning.
In the examples below, the portrait and half-figure will be molded "in two pieces", that is, the mold with each of these sculptures will consist of two parts, or, as they say, " pieces" or "shells".
The front, most part, of the mold is obviously not removable, so at the very end of the process, in order to remove the finished casting, the mold must be carefully broken. Therefore, this process of molding and casting is also called “chopping”.
First you need to decide where the boundaries of the two parts of the form will be.
The form must be able to be disassembled and removed from a model made of soft material. Therefore, one of the parts is most often made slightly or noticeably smaller, so that when disassembling the mold it can be easily separated.
The remaining part should have a large enough open part through which it will be possible to a) clear the mold of clay and b) visually verify that there is no clay left in the mold and that the entire surface has been treated with a release agent.
So, having placed in front of you a sculpture in a soft material, you need to determine where the boundaries of the parts will be, you can, if desired, outline the outline with a sharp tool.
Then, along the intended trajectory, it is necessary to set the sides from thin metal plates.
In this case, we use plates cut from thin sheet copper for this purpose. If possible, ensuring that the gaps between the plates are as small as possible.
If desired, you can go over the plates with tape and thus make the surface of the side ro V No, no gaps.
Then the next stage begins - the actual creation of the plaster mold. When molding into splits, the first layer of the mold is tinted. This is done so that when you reach it when splitting the mold, you must act more carefully - the casting will already be located behind it.
To tint plaster, it is convenient to use some inexpensive dry pigment.
It is undesirable to use any paints, such as gouache, because... the plaster may not set or gain strength.
To mix the plaster, including the first (colored) layer, we will need a container, preferably with flexible walls, such as a plastic bucket or rubber ball. This container is easy to clean later.
It is advisable to dilute the colored pigment separately in a small amount of water and mix thoroughly.
To mix the plaster, use cold water. The ratio of water and gypsum by volume is 1.5-1.75 parts of gypsum to 1 part of water.
Water is poured into the container, then the diluted pigment is added, then plaster is poured.
The plaster is given the opportunity to soak in water (1-2 minutes) and then thoroughly mixed.
An option for determining the proportion between water and gypsum is to pour gypsum into water until a small “island” appears. But in order to more clearly understand the proportion obtained in this case, it is better to first measure the volume with two cups (one for water, the other for plaster), noticing at the same time what size the “island” is obtained with a larger or smaller proportion. After a while you will be able to knead by eye.
The development of a sense of consistency of the mixture is also greatly facilitated by mixing with your hands, while you can control the absence of lumps.
For mixing small volumes, it is convenient to use your hands or a special spatula; for large volumes, it is convenient to use a traditional whorl in the form of a cross, stuffed onto a long handle (picture below), or an ordinary modern metal whorl inserted into a drill, as is done at construction sites for mixing mortar. If you buy such a whorl, it is better to take a rarer option - twisted in the opposite direction, when rotating which the solution will not rise (as is more convenient for concrete), but, on the contrary, will be directed to the bottom - in this case, there is less chance that if you press it carelessly When you press the drill button, you and the entire surrounding area will be in plaster.
Before applying plaster, the surface of the clay work must be sprayed with water from a spray bottle. The gypsum spreads better over a surface moistened with water and fills all the unevenness. Applying plaster to a surface that has not been wetted with water can cause the clay to absorb water from the plaster applied to it, causing bubbles and voids to form on the surface of the mold. In addition, plaster devoid of some water becomes very porous, and this leads to the fact that the release agent is very strongly absorbed into the surface of the mold and the mold can be difficult to separate from the casting. At the same time, the water must have time to drain from the surface of the clay so that the gypsum does not liquefy due to it.
Let the plaster thicken to the viscosity of kefir and spray the surface of the sculpture, trying to get the plaster into all the grooves and crevices.
This stage is called "splashing". Its task is to ensure that the plaster reliably covers the entire surface, leaving no bubbles or empty spaces. To do this, in critical places you can lightly blow on the surface of the plaster, thus expelling possible bubbles.
If the entire surface is covered, wait a little. Gradually, the gypsum we diluted thickens, and we apply a thicker layer over the “splash.” We remember that plaster that begins to thicken cannot be stirred again, otherwise it will “rejuvenate”, that is, it will not be able to set.
It is important to try to ensure that the color layer lies more or less evenly, without places that are too thick (more than 1 cm) or too thin (less than 3 mm). Places that are too thick make the idea of dividing into layers for easy splitting pointless. Places that are too thin can break off from the outer, white layer in the most critical places, severely damaging the future plaster cast.
It is advisable to quickly cover the entire surface with gypsum, avoiding the formation of matte areas before a layer of at least 3 mm has been built up. The dullness of gypsum with a small thickness indicates that the clay has absorbed water from the gypsum. This can lead to the fact that if the mold is not well lubricated from the inside, this layer will be difficult to separate from the casting.
In order for the splitting of the form to occur in layers (first the top, then the color), there must be adhesion between the layers, but it must be weak.
For this purpose, it is advisable to walk the surface of the colored layer with thinly diluted (to the thickness of milk) clay. Thanks to this, adhesion to the next layer will be achieved mainly due to surface unevenness.
Some masters, for example D. Broido in his book “Guide to the gypsum molding of artistic sculpture” (“Art”, 1937) advise coating not the entire surface of the colored layer with liquid diluted clay, but only the protruding and most critical places, but to the required, weak degree adhesion of the colored and subsequent layers is achieved through proper work with the consistency of the gypsum - the next, non-colored layer of gypsum should begin to be applied when it begins to thicken.
As you can see, we are not covering the edges; they still need to be one with the next layer.
In the example given there were no sides, that is, the form will consist of one piece. This can be done if you are confident that all the clay can be removed through the lower open part.
And here are more examples of smearing with liquid clay the middle part of the colored layer, or only the protruding and most critical parts, as some authors advise.
For these purposes, it is convenient to dilute the clay in a small glass until it becomes milk or cream.
After waiting for the clay to dry, apply the next (not colored, just white gypsum) layer, it should be 2 to 5 cm thick depending on the size of the mold. Some authors advise strengthening it with reinforcement (wire). Some people lay pieces of wire directly onto the colored layer before applying the white. Someone is in the process of applying white. Personally, I have no confidence that this should be done. On the other hand, when splitting a mold, pulling out parts of the reinforcement greatly simplifies and speeds up the process of splitting itself.
It is also advised to start applying the white layer when it begins to thicken, then the adhesion between the layers will be quite weak and you can even do without coating with clay. At the same time, of course, you need to have time until the plaster begins to set; we remember that you cannot knead the setting plaster, otherwise it will “rejuvenate” and cannot set.
It is important to ensure that the outer layer is not unexpectedly too thin, especially on protruding parts such as the nose. During further cleaning and washing of the mold, thin places may be accidentally pressed through and holes in the mold may form in these places.
It is also important to avoid voids between the colored and white layers, since this, when processing the mold from the inside, can lead to shedding of the colored layer and, accordingly, damage to the casting.
To obtain a uniform second layer, you can first lay plaster around the perimeter, creating a kind of frame of uniform thickness, and then apply plaster not randomly, but moving from the edge and maintaining the thickness.
The proportion of gypsum to water in the white layer should not be stronger than in the first layer, but rather a little weaker. A stronger second layer may crack as the plaster sets.
After waiting for the layer to set, turn the work with its back side towards you and carefully remove the plates. In this case, you must pull carefully along the edge of the mold, so that the gap from the plates does not widen.
If on the opened edge of the mold you can see differences in height from unevenly aligned plates and the shell (empty spaces) - don’t be upset, just all these defects will need to be covered with clay a little later to prevent the back half of the mold from catching on the front.
Then we remove the sides, trim half or slightly less of the opened edge of the plaster mold with a knife and cut out holes for better fixation of the parts of the mold to each other. All this can be seen in the photograph.
Some craftsmen place the plates especially carefully and do not remove them during molding, and make the edges of the plaster mold wider than the plates. In this case, semicircular recesses are made on the part of the mold protruding beyond the edge of the plates.
Lubricate the edge of the plaster mold with thinly diluted clay , if necessary, we fill with clay the existing cavities (voids) in the side of the mold; if there are hooks from height differences between the plates, we also fill them and stick clay “wedges” - we will need them to open the shape.
Then we dilute the colored plaster, let it thicken to the state of kefir and make a splash, after the gypsum has thickened a little more, we finish the colored layer, let it set, coat the protruding parts with liquid clay, let it dry, apply a white layer, 2 to 4 thick cm.
Since clay work tends to dry out, all shaping should be done within 2-3 hours. In reality, everything happens faster, but if the form is large and complex, the task should be to cover the surface of the clay with plaster as quickly as possible, at least a colored layer and a little white, and then build up a sufficient thickness of the white layer. In my practice, there was a case when two novice molders for some reason molded a multi-part mold from a clay work for more than one day, but they forgot about the need to constantly maintain the moisture of the clay. Accordingly, the mold was made, and the work gradually dried out... When the future molding masters disassembled the mold and made a test casting, they themselves and all their colleagues were quite surprised :)
After half an hour or later, you can begin to open the form. To do this, we prepare wooden wedges and carefully begin to hammer them into the places where clay “wedges” stick out at the joints of the mold. If, when applying gypsum from the back side, part of the plaster gets on the front side and the joint between the front and back sides becomes invisible and the form may not open due to sagging, all these sagging can be cut off with a knife (wet plaster is easily cut), or using molds larger ones - with a small hatchet. When cutting away the beads, the joint line becomes visible due to the fact that the edges of the front side mold were painted with liquid clay. This advice is also relevant if, for some reason, clay “wedges” were not made and wooden wedges have to be driven directly into the joint of two parts of the mold - then this joint, of course, should be visible.
We hammer in a little and everything in parallel, then pour water on the pegs, wait for them to swell and begin to open the mold. You should not act too hastily - too much force can cause the mold to crack.
If this suddenly happens, do not despair, it is simply advisable to notice it in time and if only part of the mold begins to come off, try to return it to its place, so that the edges of the crack are connected as much as possible. After this, you need to dilute the plaster, moisten the cracked area with water and apply a bun 1-2 cm thick and 5-7 cm wide to the sides of the crack. You can also insert a piece of plastic or metal mesh into the plaster as reinforcement. Then you need to wait until the plaster sets (heats up and begins to cool) and continue opening the mold slowly and carefully, trying not to put stress on the cracked area.
When a gap forms, carefully, without sudden movements, separate the parts of the form, if necessary, helping yourself with a chisel or spatula.
If, despite all attempts, the form still does not open, you should not try to open it using rough and sharp actions - it will be so easy to damage it. It’s better to check once again that the shape of the pegs matches (maybe they are too narrow and are simply making their way, instead of carefully pushing the halves of the form apart), water again, carefully and evenly hammer in all the pegs on all sides.
Also in such a situation, you can dismantle the base of the frame and give yourself access to the lower, open part of the form. Next, turn the mold over with the open part up, gradually pour in water, soak it and begin to remove the clay. It could also happen that there are unevenness on the surface of the back of the work, even minimal hooks, and the clay has become too dense (due to insufficient watering during the creation of the work) and cannot come off. If the neck of the mold is wide, you can remove a significant part of the clay before opening the mold, and this must be done anyway. If the neck is narrow, pouring water into it will gradually soften the clay. After some time, you need to try to open the form again.
If, during the process of opening the mold, the necessary pieces still come off from it, you need to collect them and mount them back, either by carefully connecting them and sticking a plaster bun on the outside, or after cleaning and drying the mold, glue them with second glue.
Then you need to clean the mold from clay/plasticine. We do this with a loop stack, a wooden stack and rinse the mold with water and a brush.
If you need to remove a lot of clay or plasticine, then it is convenient to do this with a loop stack, provided that it is strong enough. In this case, you need to act carefully so as not to cut off the parts of the form protruding inward.
When the bulk is taken out, it is better to switch to a wooden stack.
If it so happens that the clay has become very dense and is difficult to remove (as a rule, due to the fact that the work was carried out for a long time and was rarely watered), you can soften it by soaking it in a bath. It is advisable to ensure that clay and pieces of gypsum do not clog the drain.
In a similar case with plasticine (if it is difficult to remove due to its hardness), you can warm it up with a fan heater.
When removing plasticine, prying it from the sides, you can remove almost all the work at once. When removing the frame, you must pull carefully so as not to catch the frame wire and damage the shape.
When the mold is cleared of clay, it must be washed completely, carefully rubbing the rough edges and indentations with a brush. Alternatively, you can do this in the bathtub, remembering to avoid clogging the drain.
The purpose of touching with a brush when washing a mold is to pry up the clay so that a stream of water can remove it, and not to subject the mold to friction. Excessive friction easily leads to distortion of the shape.
If further work cannot take place on the same day and the form must be stored for some time, it is recommended to assemble it and tie it tightly with rope or tape. If this is not done, parts of the mold, being raw and stored separately, may bend slightly (raw plaster parts may bend under the influence of gravity), each in its own direction, and later, when assembling the mold, cracks may be found.
One of the traditional options for a release agent:
The surface of the mold is covered with liquid soap several times until the soap stops being absorbed. Then thin coat with a layer of vegetable oil or Vaseline.
The basic principle when lubricating a mold with any composition is that the entire surface, without exception, should be coated with as thin a layer as possible. A thick layer of lubricant, especially deposited in the recesses of the mold, can greatly damage the casting.
In the old days, for these purposes, the inner surface of the mold was sprayed with “lye” (a strong decoction of birch ash), as it gave the thinnest separating film. To ensure that the molds lag behind the casting in this case, the mold was saturated with water in excess. New plaster no longer sticks to a plaster surface that has been wetted in excess. Cases are also described when an over-wetted mold lagged behind the casting without any lubrication. Naturally, it’s better not to take risks in your first molding experiments. But experimenting with the adhesion of gypsum to surfaces of different humidity and thoroughly soaking the mold with water is certainly useful.
Modern release agents in aerosol packaging deserve attention - spraying the surface of a mold, especially a complex one, with an aerosol is much faster than carefully covering it with a brush. It is fundamentally important that before using any of these compositions on the surface of the mold, be sure to conduct an experiment on any piece of plaster.
The parts of the form are connected, tied with rope; if there are cracks at the joints, they are filled with clay. Or you can simply fasten them with plaster, placing it on the outside at the joints, 5-8 cm wide.
The mold is then turned over, set firmly and filled with plaster.
After mixing the gypsum, remove the foam from its surface with a spatula. The plaster is poured into the mold in a thin stream along the edge of the mold - this also reduces the number of bubbles on the casting.
If you need to get a hollow casting, gypsum is poured to about a third of the volume and the mold is placed almost on its side and turned so that the gypsum gradually settles on the walls, then the gypsum is poured back into the mixing container. Then the mold is not completely filled in again and the process is repeated until the plaster begins to thicken. The remainder of the plaster is smeared along the edges of the hole and these edges are leveled with a spatula along the edge of the mold.
If it is not possible to achieve the required thickness in one batch, a second and sometimes a third portion of gypsum is mixed. In these cases, the solution is mixed weaker than for the first (outer) layer, otherwise the casting may break.
15 minutes after pouring or later, you can start chopping. This must be done carefully, using a chisel or chisel and a mallet or hammer. The blows must be directed not inside the mold, but tangentially, so that the mold is destroyed and no force is transferred to the casting. The tool should not be too sharp, since its purpose is to split, not cut.
If possible, you should first remove the top (white) layer of plaster, and remove the tinted one more carefully. However, in practice, often in some places the plaster can be removed immediately, exposing the casting. In this case, it is advisable to still try to remove the top white layer in other places first.
Because chopping takes some time, the person performing it becomes tired and may become less careful, and may be tempted to hit harder and more often in order to complete the process as quickly as possible. At this moment, the person loses caution and hits the sculpture through the form - either makes a notch on the sculpture, or chips off part of the sculpture along with the form.
It is good if the color layer was applied at a more or less uniform thickness. Then you can quickly get used to striking with the required force and not hitting the casting. Of course, this will work if you have the patience to remove all the white layer first when chopping.
It is advised to start chopping the colored layer from some convex and smooth part of the sculpture.
When you approach the surface of the sculpture during the chopping process, you should slow down and remember that even if the work is completed half an hour later, nothing bad will happen. And in any case, restoring the “cut” surface of the sculpture may take much more time.
When chopping very small things, the outer layer is gradually cut into squares and carefully chopped off with a knife. Do the same with the colored layer, increasing caution.
If the sculptor does not shape and hammer out himself, but turns to professionals, “shapers” for help, this is, on the one hand, good, because... a good shaper will carry out the entire process of molding and casting much better, although he will charge a lot for his services, but you need to make sure that the same shaper, if it kills the mold, in no way tries to disguise it (plaster it with plaster or, as they say, “flind it” ) on your own, because what in the eyes of a non-sculptor will be “normal” and “smooth”, for a sculptor may mean a complete loss of shape in this area.
You need to work especially carefully and without haste when approaching small parts, because if something is accidentally knocked off and flies into the mass of fragments of the mold, you may never find this part and will have to patch it up again.
In this regard, the following case can be cited...
In one of the sculpture factories located in Moscow, the sculptor asked one molder to mold and cast a small figurine of a seated Pushkin. The shaper carried out the work successfully, but when the time came to break up the mold, he was already somewhat “under the weather” (which is generally typical for shapers and other workers of our vast Motherland). And Pushkin had a top hat on his head. And the shaper accidentally knocked it off and didn’t notice where it flew off (the sculpture, I remind you, was small). I searched and searched for him among the fragments, but did not find him. As a result, without hesitation, the resourceful shaper took some plaster and created a hairstyle on Pushkin’s head as best he could.
The sculptor came to accept the work, did not notice anything, paid and took Pushkin away.
After a while he comes running and asks:
- “Where is the cylinder?”
What a cylinder, says the formator, there was no cylinder!
- How could it not have happened when it was! Where did you put the cylinder?
Yes, there was no cylinder. When you brought me the sculpture, there was no top hat on it. I molded everything as it was.
Why don’t I remember my work, or what? You must have lost it during the chopping!
No, there was no cylinder, there was no, there was no, there was no! - the formator never confessed.
The seams can be cut with a knife immediately while the casting is wet, or later, after moistening it with water.
On When a casting is released from the mold, bubbles are usually present in small (and sometimes large) quantities, and sometimes there may be casting defects (unspilled areas). To seal large (from 4 mm) defects, it is convenient to use gypsum. For these purposes, gypsum is diluted very thinly (1: 1 or so), and the embedding site is heavily moistened with water. If you try to fill the missing places with gypsum of normal consistency or do not sufficiently moisten the casting itself with water, then the main mass of the casting will instantly draw water from the newly applied plaster, which in turn will become very hard, inconvenient to handle, and if more force is applied, it will easily chip off in a whole piece. Having applied weak plaster to the dampened area, it is best to give it the desired shape as soon as it begins to thicken.
For smaller holes it is more convenient to use putty, for example Maxi , or other “finishing” construction putty.
The same recommendations can be applied not only to sealing casting defects, but also to cases of further refinement of the casting already in plaster. If you need to cut something with a knife, and the casting has already dried and become hard, then the desired place can be moistened with water using a brush. And in this regard, one interesting factor should be voiced that sometimes awaits a beginning sculptor - this is the desire, having received a plaster casting, to smooth and polish it all. Despite the fact that the same places, while the work was in clay, did not cause concern at all with their “roughness”, but looked quite natural. But something happens in the plaster, the perception changes, and at this moment you can sometimes literally ruin the work by starting to smooth and lick everything, which is why the sharpness and liveliness of the form and surface can be lost. Subsequently, if the work is transferred, for example, to bronze or simply tinted in any shade, the perception changes in the opposite direction - unevenness and roughness cease to irritate, and again begin to be perceived as natural manifestations of the sculpting process, which do not necessarily have to be hidden in any way in order to achieve a smooth surface. Therefore, a novice sculptor can be advised not to rush to smooth out his work, but instead, try to tint, first roughly and approximately, and thus understand how it will really look.
The finished casting can be tinted in any color if desired.
If a work is valuable and successful for you, you need to protect it, using it as models. And for further sale, gifts, etc. use plaster removed from it, or transferred to another material copies.
Oleg Toropygin
P.S. And for those who are really interested in the technology of molding into plaster, we can recommend getting or finding this book in electronic form - D. Broido’s “Guide to Gypsum Molding of Artistic Sculpture”, published by the publishing house “Iskusstvo” back in 1937...
The article is aimed at beginner sculptors and molders, if you have anything to add, you can send your valuable thoughts to -This email address is being protected from spambots. You must have JavaScript enabled to view it.
This separator recipe is used by craftsmen from different countries. I studied with a Bulgarian ceramist, took a lesson with an old-school Russian model maker, and rented a corner in a Czech ceramics workshop. Everyone had the same recipe. For small forms, you can use both cream and Vaseline; you need to smear them with a thick layer. With larger forms everything is more complicated. And it is advisable to spread a thin layer to get thin seams.
Modern pre-made plaster releasers do not work well.
This popular separator is made from bar soap and diesel fuel. You need to take the cheapest soap, without fragrances, lotions or moisturizers. In Russia it is “Children’s” and light “Household”. Dark "Household" will not work, it is alkaline.
The soap must be grated, on the side with round holes with torn edges. This is quite tedious, but if you plan it into large pieces, it will be difficult to dissolve it in diesel fuel without lumps. Pour the planed soap into a glass of diesel fuel and place it in a water bath, stirring constantly. Important: do not use a gas stove; diesel vapor may ignite!
We add diesel fuel from time to time. Soap bars come in different sizes, and it is not known how much diesel fuel is needed. We want to get a consistency that is thicker than toothpaste, but softer than shoe polish - about somewhere in between. If, after a long stirring in a water bath, a homogeneous consistency cannot be achieved, you can break up the lumps with a blender.
1 bar of soap will take approximately half a liter of diesel fuel. But take diesel fuel with double reserve. Firstly, it may take more than 1/2 liter, and secondly, lubricant that has been stored for a long time begins to dry out on top, forming interfering crusts, because Diesel fuel is very volatile.
I put some of the lubricant in a second jar and fill it with a layer of the remaining diesel fuel for storage.
The resulting separator is applied with a bristle brush in a thin layer - simply spread with a brush, as if painted. After a couple of minutes - the second layer.
The finished form must be rinsed without delay. Wash with a foam sponge with hot water and liquid soap. I like Ariel-gel in this application better than liquid dish soap. You should not wash your hands with soap; it contains emollient oils. Then rinse with running water and soak in a warm soda solution. There is no need to make a solution that is too concentrated; it will be difficult to completely wash it out of the mold, and the mold will become covered with soda “stalagmites.” Which is not scary in principle; you can simply sweep them away with a brush.
You can do without soda, but you don’t have to do it once at a time, and redoing all the molding work is hellish work. If the crock is poorly sucked, then one of the reasons is clogged pores with poorly washed lubricant. This applies to any lubricant, cream, and Vaseline. And if small forms can be washed properly without soda, then large ones cannot be washed so easily.
And at the same time I’ll tell you what is the most convenient way to cover the model.
If you're going to mold a life-size head of David, you can't beat traditional clay. We can do without clay, it carries terrible dirt, even more than plaster.
Regular modeling plasticine for artists contains wax, which is difficult to wash out. In addition, it is quite hard; it is difficult to cover large models with it.
The best covering, in my opinion, is Jovi children's model plasticine in large packs. It is soft, you don’t need to heat it up, and it evens out easily. And it doesn't contain wax, so it washes off easily and easily. And another plus of Jovi is that it does not melt when the plaster heats up.
Loading...