Hand molding in plaster molds If you want to make several identical clay products, you can use plaster molds. Why gypsum? Firstly, gypsum is a fairly common and cheap material, and secondly, complex structures can be cast from it.

Types of tiles Tiles are one of the most versatile facing materials. These are multi-format plates of relatively small thickness, made of different material– ceramics, natural stone, glass and

Tiling with gypsum binders Below is technological process facing with gypsum decorative tiles of walls and partitions of internal premises.

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

1) tape-harness - popular in the northwestern regions of Russia and Tajikistan;
2) East Siberian modeling of vessels from several parts with junctions running in the vertical direction;
3) Central Asian modeling of vessels from four horizontal belts;
4) molding by knocking out;
5) kneading into the finished form:
6) last in the list, but not least - drawing a vessel from one piece of clay on a foot potter's wheel. True, there is another method for making clay vessels, but it can hardly be singled out as a separate, seventh, method, since only very monotonous vessels for wine and grain were made with it in the Neolithic era.

In this way, the vessels were "erected" by hand, like building structures. From coarse fabric, according to the outlines of the future vessel, a form was sewn, which was filled with sand. Outside, the form 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 - sometimes remained on the inside of the vessel.

Separately, it must be said about the casting method, when the slip is poured into a plaster mold. Today it is the most common way to produce ceramic products, including majolica, faience and porcelain. It appeared in the Middle Ages and, due to its technological simplicity, began to quickly 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, revealing the remarkable properties of clay and at the same time serving a person. So let's talk about them in more detail.

To work in the first way, you need a turnstile (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. Having cut off the excess, leave an even clay circle on it and along its edge begin to wind the wall of the future vessel from clay bundles. This process is similar to the process of weaving a basket, but without vertical rods, since the bundles, unlike the vine, stick together with each other, and as the vessel wall grows, they are leveled with fingers or a stack.

Second production method earthenware easier to describe, but harder to apply. 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. It is necessary to glue the clay patches in a dried state (in leather-hard, as ceramists call it). On the surfaces to be glued (seams) it is necessary to apply a notch with a scalpel and lubricate with a slip like glue. This method of working with clay has recently become widespread. In the literal sense of the word, ceramists “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 patches already 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 work with clay, but it is the most difficult, and I now have great difficulty believing that in this way our ancestors made rather thin-walled vessels. (But it’s hard to believe that people, rubbing their palms wooden stick rested against a log, fire was made.) To make a vessel by knocking out, you take a piece of clay, press a rolling pin into it, but not through, but leaving a layer that will serve as the bottom of the future vessel. Then put the rolling pin horizontally with the clay and begin to expand the hole in the clay, as if rolling it from the inside. When the wall of the vessel begins to sag under its own weight, place the vessel on the bottom and, striking with the rolling pin from the inside (outside of this, substitute a specially rounded plank or palm), bring the wall thickness of the vessel to the desired - 5-6 mm. Then stick the neck made in advance to the cylinder or pot obtained in this way. The bottle or bottle is ready.

The fifth method - otminka in the finished form - is a repetition of pre-prepared forms with clay. The form is made from almost any material: wood, metal, gypsum, it can be either solid or composite. In the manufacture of solid molds, it must be taken into account that the clay products crumpled in 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 the clay was able to show everything that it is capable of.

At first, people worked for. manual potter's wheel, which severely limited their capabilities, as they worked with one hand, the second rotated the circle. With the invention of the foot circle and the release of the second hand, man was able to completely liberate the clay.

The foot circle used by the old Russian masters was made of wood (with the exception of a metal rod that acted as a bearing) and consisted of two disks: the upper one was 40 cm in diameter and 5 cm thick and the lower one was 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, by six or eight bars, set 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 circle-flywheel and was fixedly fixed with its lower end (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, as if 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 tow. During operation, to make the circle easier to move, the shaft at the lower circle was wetted with water, and the upper metal rod was lubricated with vegetable oil.

The modern potter's wheel is equipped with an electric motor. How to work on a potter's wheel? Of course, it is difficult to teach this in words. Chief Assistant here - 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, as it helps to feel the harmony of form.

To work on the potter's wheel, you need certain abilities, certain data. The first thing you need to start with, as when learning to play the piano, is with the position of the hands. Remember, if you do not place your hands correctly, you will never achieve good results. You will not be able to feel the wall thickness of the vessel, which means that it will either come out very thick and heavy, or you will make very thin walls before you have finished making the vessel. And this simply will not 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, which potters use at the beginning of work, twisting the vessel by about one third at 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 retractable vessel is located between the index fingers, but turned out so that the index finger right hand it is located horizontally and above the thumb, and with the whole right palm you, as it were, hug the vessel; the left index finger is vertical and forms a cross with the right.

The third position of the hands is necessary for the potter mainly for the formation of 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 hand positioning, as, indeed, they appear with violinists and pianists, but these features should never distort the basic principle correct setting hands It is known that relearning is much more difficult than learning.

After setting the 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 how to crush the clay to 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 form of a hemisphere rotates smoothly on a 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 crackle out of the clay when forming a cone. When centering, you need to skillfully change the speed of rotation of the circle. With increasing hand pressure, the speed should increase. If you do not learn how to properly center the clay, you will never truly master the art of pottery, since even a small beating of poorly centered clay at the beginning of work will increase as the vessel grows and in the end will definitely tear it off the circle.

An important point in the process is fixing the bottom of the vessel. Here intuition should be connected, which can be helped. To begin with, make ordinary flower pots trapezoidal in 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 the pottery vessel should be 2-4 mm, depending on your skill, the quality of the clay, the dimensions of the product and its purpose or nature. But everything is in order.

In the center of a centered piece of clay, make a prominence with your finger, moisten it with water (when working on a potter's wheel, you must constantly moisten your hands in a basin of water) and push the clay to an imaginary bottom. Then disperse the clay with 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, basically support the clay from the inside. This is, so to speak, the main point. In the manufacture various forms hands are constantly exchanging efforts. But by no means is any of them completely weakened. You kind of pull the clay up and in, up and out, with the fingers of the right hand slightly lower than the fingers of the left, between them the clay takes the form of the letter "8". The vessel under the action of your hands grows up and in breadth.

Do not try to immediately make a vase or a glass. Practice the individual operations first. And do not regret crushing the first clumsy 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 do not contradict her, for clay holds only harmonious forms. Do not forget about the 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, cut off the excess clay at the base of the vessel with a chisel, 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, each time you pick up a freshly twisted vessel, you will be sincerely surprised at its extraordinary lightness in relation to volume. It will seem to you much lighter 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 the manufacture of pottery. Drying the product incorrectly will negate all your previous efforts. Remember: a freshly twisted vessel is most afraid of drafts. Therefore, it is necessary to dry products in specially designated places. Products should dry slowly enough so that there is no tension 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 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, with spouts, handles and various stucco - should dry very slowly and preferably in special drying cabinets or simply under plastic wrap. But you should not overdry the product either, as it will again absorb moisture from the air to equilibrium with humidity. environment. A characteristic and important moment in the drying process of any clay product is the moment when shrinkage stops. This moment occurs 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 termination of shrinkage for plastic clays is about 10-20%, for kaolins - 25-30%. technical name this remaining part of the water is "pore water" (as opposed to the "shrinkage water" removed during the shrinkage process). Residual moisture after drying is usually 6-8%.

Shrinkage during drying is higher, the more dispersed and plastic clay. For example, Prosyanovsky kaolin has a linear shrinkage during drying -2-3%, loess - 3.5-5.5%, Gomel clay - 6.4%, Cambrian clay, on which the Pokrovskaya Ceramics artel works, - 6.4 -6.6%, hours-yar clays 8-10.5%. And one more thing: the behavior of clay depends on the duration of drying and the thickness of the vessel walls. Slow drying will shrink the clay somewhat more than fast drying. The volumetric mass of clay and the strength of products during rapid drying slightly decrease, and the thicker the walls of the vessels, the greater the shrinkage. The introduction of an electrolyte into the clay (liquid glass or clerical glue) or an increase in the amount of a leaner reduces shrinkage during drying. Be sure to use the experience of the Pechora potters in your work: so that the bottoms of vessels of small diameter do not crack during drying, they wrap the bottom of the vessel with a slightly damp cloth or newspaper for the first time of drying. So that the bottom of a dish of large diameter does not crack during drying, you need to wrap the edges of the dish with a damp cloth.

It is necessary to say about polishing. This is one of the ancient ways of decorating ceramic products. The shard in a leather-hard state is smoothed with a polisher, which is made of stone, bone, wood or metal. The surface of the shard is thus compacted and smoothed to a sheen that is retained even after firing. On the surface of a black-glazed vessel, partial burnishing creates brilliant patterns on a matte black background. We emphasize once again that polishing is carried out on an incompletely dried product. If this moment is missed and the product is dry, then before polishing it must be moistened. This can be done in several ways: washing it with a damp sponge, spraying it with water from a spray bottle, or dipping it in water very quickly.

After the product has been properly dried, you must wash it. This term refers to an operation that requires special care, as you can break the product, because before firing it is very fragile. When washing, you wipe it with a damp sponge, as if erasing dust, and at the same time, all roughness, burrs, irregularities are washed away with water and disappear.

Products are ready for firing.

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

clay casting

Page 19 of 25

clay casting

Among various ways molding of ceramic products casting occupies a special place. It makes it possible to manufacture with great accuracy many identical thin-walled vessels of complex shape, small sculptures with fine details. Clay or slip casting is based on the ability 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 thick cream in consistency.

The gypsum mold, into which the slip is poured, intensively absorbs water. At the same time, 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 earthenware is removed from the mold and dried before being fired. That's in in general terms 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 according to it, and then cast a mold from plaster according to the model.

You should start developing a sketch only after you clearly imagine the purpose of the product being developed, because the shape, proportions, size and decorative finish are closely related to it. But keep in mind, no matter how successful the sketch is, when making a voluminous thing based on it, it almost always becomes necessary to make some amendments. 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, there is sometimes a division of labor, when the sketch is made by the artist, and the model is turned by the master modeller. In order for the creative process not to be interrupted, the artist must be able to grind or cut models himself.

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

Turned and cut parts are connected into a single whole using nails, screws and waterproof glue, such as BF-2 or epoxy. The finished model is impregnated several times with hot drying oil and dried. Gypsum 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 rail-rule (33.1b) is laid on the steps. The rule serves as a support for the cutter when turning the model. If an electric motor is connected to the 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 drying oil or paraffin (33.1c) is tied around the perimeter with twine. Gypsum (33.1 g) is poured into the formwork. Thus, after the gypsum hardens and the formwork is removed, a massive cylindrical blank is formed on the disk - the head of the grinding machine (33.1d). The head is positioned in such a way that during operation the rotating model is approximately at the level of the grinder's eyes. Just as when drawing a clay product on a potter's wheel, the disk must rotate counterclockwise at a speed of 300-350 revolutions per minute. According to the principle of operation, a grinding machine resembles a lathe: chips are also gradually removed from a rotating workpiece with cutters until the desired configuration of the rotation body is obtained. But unlike a lathe, the plaster blank is positioned vertically, not horizontally.

Thanks to this, it is convenient to cast the workpiece directly on the head of the grinding machine; in addition, the master sees the product in a natural position, that is, just as if it were standing on the table. In the process of searching or refining a form, this is very important. Cutters for a model-grinding machine are called clubs (33.2b). Sticks are made of steel rods, which are mounted on wooden handles. At the end of the rod, a steel plate is attached at a right angle, having 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 cutters can be made from thick wire, the end of which is flattened and crocheted. These clubs are used when turning clay products on a potter's wheel.

Determining the dimensions of the model, and hence the workpiece, it must be taken into account 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 on the sketch, the model for its shape should be made larger, 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 = 100 x a / 100 - b, where a is the size of the ceramic product after drying and firing, b is air and firing shrinkage in percent. Suppose that the height of the finished ceramic product should be 250 mm with a 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 it means that 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 empirically. The solution 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 on the gypsum head a shell in the form of a cylinder, rolled up from thick cardboard or roofing impregnated with linseed oil (33.3a). Fasten 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.

In the formwork fixed on the head of the grinding machine, pour the gypsum mortar to the top (7 parts of gypsum 10 parts of water). As soon as the gypsum hardens after 8-10 minutes, remove the formwork and, having marked with a pencil all the main dimensions (33.3b), proceed to turning the model. Put the right one on the upper steps, lean the club on it and start removing chips from the rotating gypsum blank (ZZ.Sv).

Gypsum saturated with moisture is cut very easily. It should be kept wet until the end of turning. When drying, the gypsum must be moistened with a sponge moistened with 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 plaster mold. The simplest plaster form consists of two halves. Before you start casting the mold, make a shallow hemispherical cutout from the side of the bottom at the base of the model. This will ensure the stability of the future casting. Install the roofing formwork on a flat shield, having previously lubricated its internal 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 completing the preparation, pour a layer of gypsum 10-15 mm thick (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 by pressing its base into the soft gypsum. Then add gypsum to the formwork so that the solution is at the level of the most convex sections of the model.

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

Having removed the formwork, cut with a knife along the entire perimeter of the rebate (quarter), which will later be part of the locking connection of the two halves of the plaster mold (34.2). Lubricate the cut planes with a release agent and place them back into the formwork, which must now be filled to the top with gypsum mortar (34.3). After the gypsum has hardened, remove the formwork and apply a line (34.3a) on the side surface, running along its axis and crossing 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 drawing the line, the hardened halves of the mold are separated and the model (34.4) is removed from it. The form must be dried already without a model for two to three days. It will dry much faster if it is dried near the stove or near the central heating battery. The form is ready. Now you need to prepare a slip - elutriated liquid clay. The method of elutriation 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). Porous gypsum will immediately begin to absorb moisture from it. This is easy to guess by how quickly the slip level will fall 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 absorption of moisture with the simultaneous growth of a clay layer on the walls of the mold is called by ceramists "sucking a shard".

Immediately after pouring the slip, this process goes very quickly, then slows down and stops altogether. It is at this point that the slip must be drained (35.2). On the walls of the inner surfaces of the gypsum mold, a layer of clay remains in a pasty 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 and its walls have separated from the mold, carefully remove the upper half and also slowly remove the casting from the lower half of the mold (35.4).

While the product is not yet completely dry, it is mandreled: with a knife, relief-protruding seams are cut off, formed in some places at the joints of the plaster mold; close up with soft clay all kinds of dents, indentations and scratches; after that, the surface is smoothed with a moistened sponge. If the product is dry, then the irregularities can be eliminated with sandpaper. After 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 200 castings can be made in one mold. Of course, a vessel based on a body of revolution can also 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).

A model vase is made from a rectangular block of wood, to which legs and necks, machined on a lathe (36.1), are glued. A relief is cut out on one or two walls of the model. The finished model is cleaned with sandpaper and soaked 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 is used, assembled from four planks (36.2). The formwork and pallet are lubricated with separating mastic and liquid gypsum is poured into it so that exactly half of the model is in it. The lock connection is obtained by cutting out in the lower half of the mold at the corners of the conical recesses (36.3a), which are lubricated with mastic. After pouring the second half of the mold (36.4), the gypsum fills these depressions, forming spikes. When assembling the mold, the spikes will precisely 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 cast in a manner already known (36.5).

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

The form, or mandrel, is made of plaster. After slip is poured into the mandrel, it absorbs water. Clay settles and hardens on inner surface forms, 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, fireclay, electrolytes and dyes. For different types products choose the composition that is most suitable for them.

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. Production of two classes of castings is possible: thin-walled and thick-walled (solid). Against the backdrop of potter's wheel technology or hand molding, the process looks quite complicated. Its application requires certain skills and experience. Even experienced craftsmen usually have to modify casting molds. The whole technological process from the beginning of the development of the sketch to the receipt finished product may 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 chosen technology, to provide in the form of sprues of sufficient cross section and in places that provide the best filling of the mandrel and fit to the model.

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

Models are made from materials such as plasticine, plaster, wood, ceramics or silicone. Using the model, the craftsman makes a collapsible form of 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 slurry. The form is disassembled, the model is retrieved. The mandrel is being prepared for casting. The slip is diluted and thoroughly mixed immediately before casting.

The actual casting process consists of the following steps:

• Pouring the slip into the mold
• Removal of excess solution
• Casting drying
• Separation of the casting from the walls of the mold.

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

Subsequently, the casting must be fired in a muffle furnace, as well as a product made on a potter's wheel or hand molded. Products made by slip casting can also be glazed. Glaze slip is applied to the surface. After that, the products are fired again. The components of the glaze are sintered, forming 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. The composition of the slip, in addition to clay and water, includes various additives that change the consistency and other properties of the suspension. Used as supplements

• Other types of clay
• Sand
• fireclay
• electrolytes
• Dyes

The most important equipment are molds for casting. The quality of the final product directly depends on the thoughtfulness of the design and workmanship. Gypsum molds are used in slip casting. The mandrel is usually made in two parts. To accurately match the two parts, one of them is provided with protrusions, and the other with depressions corresponding to them along the profile. In artistic casting, which is distinguished by small series, parts of the mold are held together with rubber bands. A plaster mold for slip casting has a limited service life, and when planning the production of large batches (for example, tiles), it is necessary to provide for the manufacture of several mandrels for each product.

Important! The form must be made only from high-quality sculptural plaster. Gypsum must be downy, free of foreign inclusions and lumps. Mandrels made from high quality gypsum are able to withstand over a hundred castings. If the gypsum is of poor quality, then after a dozen castings, the walls begin to crumble and crumble.

Forms that have become unusable can be crushed with a hammer, sifted through a fine sieve and added to the gypsum mortar for casting new mandrels in a ratio of not more than 1:10.

Main problems in slip casting

Thickening of the solution in the form

The solution can thicken just by being in the mandrel. Therefore, before draining, it is better to activate the slip poured into the mold by light agitation, rotation or light shaking.

Gate clogging

If a mold with a small sprue is used, clean the hole with a thin spatula before draining.

Some novice craftsmen cut the sprue crater without touching the hole and being afraid to damage the casting. To keep the sprue opening free, you can insert cocktail tube trimmings into them.

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

After the slip is drained, the piece of 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 form must be installed in an inverted position. If you return it to the original, streaks of slip are formed along the walls of the product, and the wall thickness changes. Different wall thicknesses will lead to an increase in stresses during firing and even cracks along the streaks. The casting may be hopelessly damaged.

Incomplete draining of the slip from the mold

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

Features of thin-walled slip casting

If you need to get 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 time the solution is 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 crock also increases.

During the test pouring, the slip is poured into the mandrel to the top. Every 5 minutes, the thickness of the deposited layer is measured with a 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.

Application of slip casting

Clay slip casting is used quite widely both in industry and in art crafts.

Industrial production includes sanitary ceramics, the production of figured elements for interior decoration, tiles and stove tiles.

Separately, it is worth noting the production of high-voltage insulators. Porcelain insulators combine affordable price with excellent electrical characteristics, resistance to temperature changes and excellent durability. Their disadvantage is their high fragility. Recently, they began to lose their positions in the market to products made from modern plastics.

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