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There are traditional techniques for working with clay. There are only six of them:

1) tape-harness - popular in the northwestern regions of Russia and Tajikistan;
2) East Siberian sculpting of vessels from several parts with joints running in a vertical direction;
3) Central Asian sculpting of vessels from four horizontal belts;
4) forming by knocking out;
5) kneading into finished shape:
6) last but not least on the list is the drawing of a vessel from one piece of clay on a foot potter's wheel. There is, however, another method of making earthen vessels, but it can hardly be distinguished as a separate, seventh, method, since it was used to make only very uniform vessels for wine and grain in the Neolithic era.

In this way, the vessels were "erected" by hand, like building structures. From coarse fabric, a shape was sewn according to the outlines of the future vessel, which was filled with sand. Outside, the sand-filled mold was coated with clay. As the vessel dries up, the sand is gradually poured out of the bag, and the vessel was burned in the fire. An imprint of the fabric - the former shell of the mold - sometimes remained 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 way of producing pottery, including majolica, faience and porcelain. It appeared in the Middle Ages and, due to its technological simplicity, quickly began to replace 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 a person. Therefore, we will tell you more about them.

To work with the first method, you need a turnsette (a round table made of metal, plastic or wood rotating on an axis) or a similar object replacing it. On a rotating surface, you need to stick a cake rolled out with a rolling pin. Cutting off the excess, leave an even clay circle on it and start winding the wall of the future vessel from clay bundles along its edge. This process is similar to the process of weaving a basket, but only without vertical rods, since the ropes, unlike vines, stick together, and as the vessel wall grows, they are aligned with fingers or a stack.

The second method of making pottery is easier 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 should be glued in a dried state (in a hard leather, as ceramists call it). On the surfaces to be glued (seams), it is necessary to apply a notch with a scalpel and lubricate it, as if with glue, with a slip. 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, from the simplest household items to complex sculptural compositions. By placing various textured fabrics on the table when rolling the clay, you can get clay patches with the desired pattern. Now 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 to be glued.

Fourth way working with clay, but it is the most difficult one, and now I can hardly believe that our ancestors made fairly thin-walled vessels in this way. (But it is also hard to believe that people, rubbing a wooden stick rested on a log in their palms, produced fire.) To make a vessel by knocking out, you take a piece of clay, press a rolling pin into it, but not through and through, but leaving a layer, which will serve as the bottom of the future vessel. Then put the rolling pin along with the clay horizontally and begin to expand the hole in the clay, as if rolling it from the inside.When the wall of the vessel begins to bend under its own weight, place the vessel on the bottom and, hitting the rolling pin from the inside (from the outside, substitute a specially rounded board or palm), bring the thickness of the vessel wall to the required one - 5-6 mm. Then stick the neck made in advance to the cylinder or pot obtained in this way. The bottle or crinkle is ready.

The fifth method - kneading into a finished form - is a repetition of pre-prepared forms with clay. The form is made from almost any material: wood, metal, plaster, it can be either integral or composite. When making one-piece molds, it should be borne in mind that the clay products crumpled in them must be freely removed.

These methods of processing clay were used in the manufacture of various household items until an unknown genius, who can only be compared with the inventor of the wheel, created a potter's wheel. And only on it could the clay show everything that it is capable of.

At first, people worked for. hand pottery wheel, which greatly limited their capabilities, since they worked with one hand, the other rotated the circle. With the invention of the foot circle and the release of the second hand, man was able to finally liberate the clay.

The foot circle, which was used by the old Russian craftsmen, was made of wood (with the exception of a metal rod, which played the role of a bearing) and consisted of two discs: 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 discs were reinforced 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 with its lower end motionless (either by driving into the ground through the floor of the workshop, or by attaching a "foot" to a thick board nailed tightly to the floor of the workshop). A metal pin was driven into the upper end on which, like on a bearing, wooden twists 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 brushes. During operation, to make the circle easier to go, the shaft at the lower circle was wetted with water, and the upper metal rod was lubricated with vegetable oil.

The modern pottery wheel is equipped with an electric motor. How do you work on a potter's wheel? Of course, it is difficult to teach this in words. The main assistant here is again your future experience. But I will nevertheless draw your attention to the main points, I will just share my own experience, which proves that the potter's wheel is a full-fledged co-author of the master, as it helps to feel the harmony of form.

To work on a potter's wheel, you need certain abilities, certain data. The first thing you need to start with, like learning to play the piano, is with the hands-on. 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 vessel wall, which means that it will either come out very thick and heavy, or you will make very thin walls before you finish making the vessel. And it just won't let you unscrew it to the end - it will collapse. There are three main hand positions when working on a potter's wheel.

The first one, which potters use at the beginning of work, twisting the vessel at this position of the hands by about one third. 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 horizontal and the fingers of the left hand are vertical.

The second position is the main one, in which you give the vessel its final shape. The wall of the pulled vessel is between the index fingers, but twisted so that the index finger of the right hand is horizontal and above the thumb, and with your entire right palm you hug the vessel; the left index finger is vertical and forms a cross with the right index.

The third hand position 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 have your own peculiarities of hand placement, as, incidentally, 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. In this case, with the palm of your right hand, you need to learn how to crumple the clay to the center, forming a cone. The right elbow can be supported by the thigh. Then, pressing on the cone with the palm of your left hand, lower it down to the shape of the washer and so on several times until the clay in the shape of a hemisphere rotates smoothly, without any beating, on the circle. The centering process not only mixes the clay and allows you to proceed to the next stage of work, but also allows you to get rid of the remaining small air bubbles that leave the clay with a bang when the cone is formed. When centering, you need to skillfully change the speed of rotation of the circle. With increasing hand pressure, the speed should increase. If you don't learn how to center the clay correctly, you will never truly master the art of pottery, as even a small beat of poorly centered clay at the beginning of the work will increase as the vessel grows and will eventually rip it off the circle.

An important point in the process of work is to fix the bottom of the vessel. This is where intuition should be connected, which can be helped. Start by making regular vertical trapezoidal flower pots with a hole in the bottom to give you a feel for the 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 character. But everything is in order.

In the center of a centered piece of clay, make a dimple with your finger, moisten it with water (when working on a potter's wheel, you should constantly wet your hands in a basin of water) and push the clay to an imaginary bottom. Then disperse the clay with radial forces to the dimensions of the future bottom of the vessel and only after that start pulling the walls. Make the main effort with the hand that is outside, and with the other, mainly support the clay from the inside. This is, so to speak, the main point. When making various shapes, the hands are constantly, as it were, exchanging efforts. But by no means does any of them completely weaken. It is as if you are pulling the clay up and in, up and out, while the fingers of the right hand are slightly lower than the fingers of the left, between them the clay takes the shape of the letter "8". The vessel grows upward and outward under the influence of your hands.

Do not try to make a vase or kinka right away. Practice the individual operations first. And do not regret crushing the first awkward work. 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, in no case contradict it, because clay keeps only harmonious forms. Don't forget about centrifugal forces, which, in general, form an earthen vessel. As the vessel grows, the speed of rotation of the circle, and hence the centrifugal force, must decrease, otherwise the vessel will simply collapse.

When finished, blot the vessel with a sponge, trim off excess clay at the base of the vessel with a chisel, let it stand for a while and wither. During this time, you can evaluate your work, and if your intuition tells you that the work was successful, take the string and cut the vessel from the circle. And when you truly master the skill of a potter, every time you pick up a freshly unscrewed vessel, you will be sincerely surprised at its extraordinary lightness relative to its volume. It will seem to you much lighter than the piece of clay from which you twist it. And it is this imaginary difference in weight that you can always measure your skill.

Next, you have to rush with the vessel, as if with a small child, because drying is a very crucial moment in the manufacture of pottery. By improperly drying the product, you will nullify all your previous efforts. Remember: a freshly unscrewed vessel is most afraid of drafts. Therefore, it is necessary to dry products in specially designated places. Products should dry slowly enough so that no tension arises inside the clay between the thinnest parts that have already dried and shrunk and are still wet. That is why it is desirable, and by and large - so imperative, that the thickness of the walls of the product is the same everywhere, and this will depend on your skill.

The most complex products - glued, with spouts, handles and various moldings - should dry very slowly and preferably in special drying cabinets or just under plastic wrap. But you should not overdry the product either, since it will again absorb moisture from the air until it equilibrates with the ambient humidity. A characteristic and important moment in the process of drying any clay product is the moment when shrinkage stops. This moment comes when the evaporation mirror begins to gradually move into the depth of the product and its surface begins to brighten. From this point on, the drying speed can be increased. The amount of water remaining after the cessation of shrinkage in plastic clays is about 10-20%, in kaolins - 25-30%. The technical name for this remaining part of the water is "pore water" (as opposed to "shrinkage water" removed during shrinkage). Residual moisture after drying is usually 6-8%.

The shrinkage during drying is the higher, the more dispersed and plastic the clay is. For example, Prosyanovsky kaolin has a linear drying shrinkage of -2-3%, loess - 3.5-5.5%, Gomel clay - 6.4%, Cambrian clay, on which the Pokrovskaya Keramika artel works, - 6.4 -6.6%, watch-yarsk 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 shrinks the clay slightly more than fast drying. The bulk of the clay and the strength of the items slightly decrease 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 softener reduces shrinkage during drying. Be sure to use the experience of the Pechora potters in your work: so that the bottoms of small-diameter vessels do not crack during drying, they wrap the bottom of the vessel with a slightly damp cloth or newspaper for the first time. To prevent the bottom of a large-diameter dish from cracking during drying, wrap the edges of the dish with a damp cloth.

It must be said about polishing. This is one of the oldest ways to decorate ceramic products. A shard in a leather-hard state is smoothed with a polish 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-burnished vessel, partial burnishing creates lustrous patterns against a matte black background. We emphasize once again that the polishing is performed on an incompletely dried product. 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, sprinkling with water from a spray bottle, or very quickly dipping it into water.

After the garment has dried properly, you should wash it. This term means an operation that requires special care, since you can break the product, because it is very fragile before firing. When washing with a damp sponge, you dwell on it, as if erasing dust, and at the same time all roughness, burrs, irregularities are washed out by water and disappear.

Products are ready for firing.

In writing this article, material was used from the Brockhaus and Efron Encyclopedic Dictionary (1890-1907)

Clay casting

Page 19 of 25

Clay casting

Casting takes a special place among the various methods of molding ceramic products. It makes it possible with great precision to make a lot of exactly the same thin-walled vessels with a complex shape, small sculptures with fine details. Clay, or slip casting is based on the property of gypsum to absorb moisture and on the property of clay to release moisture.

Slip is a clay, diluted to a state of fluidity, resembling heavy cream in consistency.

The plaster mold, into which the slip is poured, intensively absorbs water. In this case, a layer of clay mass of the same thickness is evenly distributed over the inner 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. The direct casting is preceded by a lot of preparatory work. It is necessary to complete 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 have a clear idea of \u200b\u200bthe purpose of the product being developed, because the shape, proportions, size and decorative finish are in close connection with it. But keep in mind, no matter how successful the sketch is, when making a voluminous thing from it, it is almost always necessary to make some corrections. Thus, direct work on a volumetric model can prompt the artist to make decisions that cannot always be predicted in a sketch. In production, there is sometimes a division of labor, when the sketch is done by the artist and the model is carved by the master modeler. In order for the creative process not to be interrupted, the artist must be able to grind or carve models himself.

The model can be made of wood or plaster. Models are sharpened from wood on a lathe or made with carpentry and carving tools.

The turned and cut parts are joined together using nails, screws and waterproof glue, such as BF-2 or epoxy resin. The finished model is impregnated with hot linseed oil several times and dried. Plaster models are turned on a special grinding machine, which is, in fact, a potter's wheel, on the right and left sides of which there are stepped supports (Fig. 33.1a).

During turning, a wooden lath-rule (33.1b) is laid on the steps. The ruler serves as a support for the cutter when turning the model. If an electric motor is connected to a potter's wheel, then it can be used as a grinding machine. Several rails are stuffed onto the upper disk and a formwork made of waterproof cardboard impregnated with linseed oil or paraffin (33.1c) is tied around the perimeter with twine. Gypsum (33.1g) is poured into the formwork. Thus, on the disk, after the gypsum has hardened and the formwork has been removed, a massive cylindrical blank is formed - the head of a grinding machine (33.1d). The head is positioned so that during operation the rotating model is approximately at the level of the grinder's eyes. Just as when pulling a piece of clay on a potter's wheel, the disc should rotate counterclockwise at a speed of 300-350 rpm. According to the principle of operation, the grinding machine resembles a lathe: chips are also gradually removed from the rotating workpiece with cutters until the desired configuration of the body of rotation is obtained. But unlike a lathe, the gypsum workpiece is positioned vertically, not horizontally.

Thanks to this, it is convenient to cast the workpiece directly on the head of the grinder; in addition, the master sees the product in its natural position, that is, just as if it were standing on the table. When searching or refining a form, this is very important. Cutters for a model-grinding machine are called clubs (33.2b). The clubs are made from steel rods that are placed on wooden handles. At the end of the rod, a steel plate is attached at a right angle, which has the shape of a triangle, rhombus, trapezoid, shaft, etc. Since the material being processed is soft enough, there is no need to harden the cutting parts of the cutters. Some incisors can be made from thick wire, the end of which is flattened and crocheted. Such sticks are used when turning clay products on a potter's wheel.

When determining the dimensions of the model, and therefore the workpiece, it should be borne in mind that the clay casting after drying, and then after firing, decreases by a total of 10-15%. In order for the ceramic product after drying and firing to have the dimensions previously planned in the sketch, the model should be made larger for its shape, taking into account the percentage of shrinkage, which is determined empirically. If it is known in advance, the dimensions of the plaster or wooden model are determined by the formula: X \u003d 100 x a / 100 - b, where a is the size of the ceramic product after drying and firing, b is the air and firing shrinkage in percent. Suppose the height of the finished pottery should be 250 mm with 10% shrinkage of the clay mass. According to the formula, we determine that the height of the plaster model should be equal to 276 mm. If you are dealing with the same clay all the time, 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 size of the model. Bend the ends of the compass so that the distances between them have certain proportional ratios, which are established empirically. The compass solution on one side should correspond to the actual dimensions of the clay casting, on the other - to the size that you want to take on the model. Having prepared the machine and tools, install on the gypsum head a shell in the form of a cylinder rolled up of dense cardboard or tar paper impregnated with linseed oil (33.3a). Tie the cylinder with soft wire or sew with thick threads.

The height of the shell should correspond to the height of the model being machined, and the diameter should correspond to the largest diameter of the model with a small allowance.

Pour gypsum mortar up to the top into the formwork fixed on the head of the grinder (7 parts of gypsum 10 parts of water). As soon as after 8-10 minutes the plaster has hardened, remove the formwork and, having marked all the main dimensions with a pencil (33.3b), proceed to grind the model. Put the rule on the upper steps, rest the stick on it and begin to remove the chips from the rotating plaster workpiece (ЗЗ. Зв).

Moisture-laden plaster is very easy to cut. It should be kept wet until the end of turning. When dry, the gypsum must 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 the manufacture of a casting plaster mold. The simplest plaster mold consists of two halves. Before you start casting the mold, make a shallow hemispherical cut from the bottom side at the base of the model. This will ensure the stability of the future casting. Install the tar paper formwork on a flat panel, having previously lubricated its inner surfaces with a release agent (Fig. 34).

Prepare a release agent from two parts of paraffin and five parts of kerosene melted in a water bath. After finishing the preparation, pour a layer of gypsum with a thickness of 10-15 mm (34.1) into the formwork. As soon as the gypsum 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 gypsum. Then add gypsum to the formwork so that the mortar is at the level of the most convex areas of the model.

Remember that if the level of the gypsum slurry is raised above the most prominent points, the model will not be able to be removed from the bottom of the mold.

After removing the formwork, cut out a fold (quarter) along the entire perimeter with a knife, which will later be part of the lock connection of the two halves of the plaster casting mold (34.2). Lubricate the cut planes with a release agent and reinstall them in the formwork, which now needs to be filled with gypsum mortar to the top (34.3). After the gypsum has hardened, remove the formwork and on the lateral surface apply a line (34.3a) running along its axis and crossing both halves of the mold. This is necessary so that when assembling the mold, it is possible to quickly and accurately connect one half to the other. After applying the risks, separate the hardened mold halves and remove the model (34.4) from it. The form must be dried without a model for two to three days. It will dry much faster if it is dried near an oven or central heating radiator. The form is ready. Now you need to prepare a slip - elutriated liquid clay. The method of elimination of clay is described at the very beginning of the book.

Clay casting... Pour the slip into a well-dried plaster mold to the top (fig. 35.1). The porous gypsum will immediately begin to absorb moisture from it. It is easy to guess about this by how quickly the slurry level will drop in the form. By absorbing moisture, gypsum attracts to the surface of the mold the smallest particles of clay that are suspended in the slip. Gradually, a fairly dense layer of clay mass forms on the walls of the mold.

The process of absorbing moisture with the simultaneous growth of a clay layer on the walls of the mold is called by ceramists "the sucking of a shard".

Immediately after pouring the slip, this process proceeds very quickly, then it slows down and stops altogether. It is at this moment that the slip must be drained (35.2). On the walls of the inner surfaces of the plaster mold, a layer of clay remains in a pasty state - the walls of the future vessel. After a while, the clay layer 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 is dry enough, 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, they make its mandrel: cut off with a knife the prominently protruding seams, formed here and there at the joints of the plaster form; all kinds of dents, grooves and scratches are covered with soft clay; after that, the surface is smoothed with a damp sponge. If the product is dry, then the irregularities can be eliminated with sandpaper. After the mandrel, 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 revolution can be made in another way, for example, on a potter's wheel. But there are vessels for which casting is almost the only way 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 are glued, turned on a lathe (36.1). A relief is cut 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 mold according to this model is cast in the same sequence as a round vase, only instead of a cylindrical formwork, a rectangular one is used, assembled from four planks (36.2). The formwork and the pallet are lubricated with a release compound 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 in the lower half of the mold at the corners of the conical grooves (36.3a), which are lubricated with mastic. After the second half of the mold (36.4) has been poured, the plaster of Paris fills in these recesses, forming spikes. When assembling the mold, the pins will fit exactly into the corresponding recesses and ensure that both halves are joined accurately.

The finished mold is freed from the model, dried, and then cast in an already known manner (36.5).

Slip casting is a technique for making pottery by casting into a mold, without using a potter's wheel or hand molding. It is used both in the mass production of clay, porcelain and other mixtures, and in the manufacture of small-scale and original items.

The mold, or mandrel, is made of plaster. After the slip is poured into the mandrel, it absorbs water. The clay settles and solidifies on the inner surface of the mold, repeating its relief in the smallest detail.

Slip composition

The base of the slip is clay with additives diluted with water. Usually it is diluted to the consistency of sour cream or heavy cream.

Slip is prepared on the basis of one or several types of clay, adding sand, chamotte, electrolytes and dyes. For different types of products, the composition that is most suitable for them is chosen.

Slip casting technology

The slip casting process is based on two physical phenomena: the ability of gypsum to absorb water and the ability of clay to release water. It is possible to manufacture two classes of castings: thin-walled and thick-walled (solid). Against the background of potter's wheel technology or hand sculpting, the process looks quite complicated. Its application requires certain skills and experience. Even experienced craftsmen usually have to modify the molds. The entire technological process from the beginning of the sketch development to the receipt of the finished product can take up to several weeks.

Preliminary operations

First you need to develop a sketch. When developing, it is necessary to take into account the requirements of the selected technology, provide in the form of sprues of sufficient cross-section and in places that ensure the best filling of the mandrel and adherence to the model.

Based on the sketch, you can start making the model. The model is an exact copy of the future product, but differs from it in slightly larger dimensions. This is the allowance for the inevitable shrinkage during firing.

Models are made from materials such as plasticine, plaster, wood, ceramics, or silicone. Using the model, the master makes a collapsible mold from plaster. Other materials available in the workshop are not suitable for the mandrel, since only gypsum has the unique property of sucking water out of the slip. The form is parsed, the model is retrieved. The mandrel is being prepared for casting. The slip is diluted and thoroughly mixed immediately before casting.

The casting process itself consists of the following stages:

• Pouring slip into a mold
• Removing excess solution
• Drying of the casting
• Separation of the casting from the walls of the mold.

After drying, separate the mold parts and carefully remove the product. The casting is dried; if necessary, insufficiently worked out details are straightened.

Subsequently, the casting must be fired in a muffle furnace, as well as a product made on a potter's wheel or hand-molded. Slip-casting products can also be glazed. Glaze slip is applied to the surface. After that, the products are re-fired. The glaze components are sintered to form a thin and smooth glassy layer.

Equipment and materials for casting

For casting, a slip of a certain consistency is used. It should be oily to the touch. In addition to clay and water, the slurry contains various additives that change the consistency and other properties of the suspension. Used as additives

• Other types of clay
• Sand
• Chamotte
• Electrolytes
• Dyes

The most important equipment is the casting molds. The quality of the final product directly depends on the thoughtfulness of the design and workmanship. In slip casting, plaster molds are used. The mandrel is usually made in two parts. For the exact alignment of the two parts, projections are provided on one of them, and in the other, the hollows corresponding to them along the profile. In artistic casting, characterized by small series, parts of the mold are held together with rubber bands. Plaster mold for slip casting has a limited service life, and when planning the production of large quantities (for example, tiles), it is necessary to provide for the production of several mandrels for each product.

Important! The mold must only be made of high quality sculptural plaster. Gypsum should be downy, free of foreign inclusions and lumps. The mandrels, made of high quality plaster, are capable of withstanding over a hundred castings. If the gypsum is of low quality, then after a dozen casts the walls begin to crumble and crumble.

Forms that have become unusable can be crushed with a hammer, sieved through a fine sieve and added to the gypsum solution for casting new mandrels in a ratio of no more than 1:10.

Major problems with slip casting

Thickening of the solution in the form

The solution can thicken simply by being in the mandrel. Therefore, before draining, it is better to activate the slip poured into the mold by gently shaking, rotating or shaking gently

Sprue clogging

If a mold with a small sprue is used, the hole must be cleaned with a fine spatula before draining.

Some novice craftsmen cut the sprue crater without touching the hole and fearing damage to the casting. To keep the opening of the sprue free, you can insert cuttings of cocktail tubes into them.

The form must be turned over the container for draining and blow evenly and strongly into the tube. It is important to achieve complete flow. Special attention should be paid to the forms of complex relief.

After the slip is drained, the cut of the tube must be filled with water. In the same position, sprue down, the mandrel should be placed on the plastic surface.

Setting the mold after draining the slip to its original position

After draining the solution, the mold must be set upside down. If you return it to its original value, slip streaks form along the walls of the product, and the thickness of the walls changes. Different wall thicknesses will lead to an increase in stresses during firing and even cracks along the sag. The casting can be hopelessly damaged.

Incomplete drainage of the slip from the mold

Incomplete draining can also lead to sagging and firing cracks. If a product of an intricate configuration is being drained, when draining, it is better to shake the mold at different angles, achieving complete drainage of the slip.

Features of thin-walled slip casting

If you need to obtain a thin-walled product, it is important to remember that after pouring the gypsum will immediately begin to suck water out of the slip. Depending on the residence time of the solution in the mold, the thickness of the walls of the vessel or figure changes. Clay is deposited on the walls of the mold at a rate determined for each specific configuration and specific composition of the solution. Accordingly, the thickness of the shard also increases.

During the trial pouring, the slip is poured into the mandrel up to the top. Every 5 minutes the thickness of the deposited layer is measured with a vernier caliper. Based on the measurement results, the master can calculate the time required to obtain a given wall thickness. Gypsum completely saturated with moisture ceases to absorb water, but in the case of thin-walled vessels, due to the relatively small volume of the shard, this should not be feared.

Slip casting application

Slip casting from clay is used quite widely both in industry and in artistic crafts.

Industrial production encompasses sanitary ceramics, figured furnishings, tiles and stove tiles.

The production of high-voltage insulators should be noted separately. Porcelain insulators combine an affordable price with excellent electrical performance, resistance to temperature extremes and excellent durability. Their disadvantage is their high fragility. Recently, they began to yield their positions in the market to products made from modern plastics.

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