How to quickly get clay into a plaster mold. How to remove a plaster mold from a figure. Tools and inventory for molding work
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 the inner surface of the form, 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 of 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 entire technological process from the beginning of the development of a sketch to the receipt of a 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 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, sieved 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 an 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.
clay casting
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clay casting
Among the various methods of molding 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. 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 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 modeler. 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 turned from wood on a 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 sticks (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.
When 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 lock 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).
Good afternoon, dear ones) I want to talk about how to remove a plaster mold from a simple figure. Molding is not such a simple matter, you need to take into account many nuances, but if you take everything into account, you will succeed. You can get a mold to replicate clay, faience, or porcelain figurines. So, firstly, the figure for molding should be extremely simple, with a minimum number of protruding parts. Secondly, for the first experience, I do not advise you to take ready-made porcelain figurines, if you make a mistake, you risk breaking the figurine during mold removal. The easiest way to remove the mold is from clay or plasticine, they are very easily separated from the plaster. I will mold my sculpture from fireclay clay. It has a streamlined shape and very few recesses in which the plaster can short out. More complex figures are often made from many pieces, their number can reach more than a dozen and it is extremely difficult to assemble such a shape at home, it is better to entrust such work to professionals. This figure can be made from two pieces. To do this, you need to divide the figure into two parts, along the most protruding places and build a plasticine barrier along the border of the parts, about one and a half to two cm high. This will be the thickness of the plaster mold. 
We put the figure on a flat, smooth surface (I have a piece of laminate) And from all sides we build a plasticine wall, from below, close to the figure and to the stand, trying not to even have tiny gaps (gypsum will definitely be poured into them and the shape will be broken) Plasticine I I use a hard, sculptural one to make it easier to work - I put it in a bowl of hot water, it softens and becomes very soft, and after cooling it immediately hardens. Pay attention - the places where there are obvious indentations - the mouth, flippers, the crease on the chin - I smeared with a small amount of plasticine, smoothed them out. If this is not done, then the gypsum, hardening in these recesses, can close the mold and prevent the mold from opening. This allows you not to make extra pieces. Subsequently, when shaping a figure from clay, I will work on these places separately, on the finished work-out. 
On plasticine in several places, I made round recesses with a ball - locks. it is necessary for that. so that the form closes correctly during operation and does not move. When you are convinced that the whole figure is demarcated by a plasticine wall, we begin to dilute the plaster. I did not take pictures of this procedure separately, it is simple. Tip - if you do not have a special rubber plaster, it is better to take a disposable container, which you can then throw away. For example, a blast bottle or canister cut in half. Gypsum is diluted in proportion (by weight) 2 parts of gypsum and 1 part of water. The volume is approximately 1:1. Pour water into a container (no more than half the container) and begin to gradually pour gypsum into it until a gypsum mound appears above the surface of the water, i.e., the mass of gypsum reaches the surface of the water. Then mix the mass and wait until it begins to thicken a little. it's about 15 minutes. when the plaster began to thicken, you need to act quickly.
We throw plaster on the model. At first it is still liquid and easily pours and flows down from the figure. pick it up with a rubber spatula. When the gypsum is already becoming viscous, you need to form a thickness. Try to make the mold match the model on the outside (although it is no longer visible) so that the wall thickness of the mold is approximately the same. 
Do not go beyond the plasticine barrier. After the gypsum has hardened, remove all the plasticine from the back. It's easy to do at the moment. when the hardening gypsum heats up, the plasticine itself leaves. Now you need to carefully lubricate the gypsum edges with petroleum jelly or another thick lubricant (even lithol will do). If this is not done, then the form will not open into two parts. 
Lubed? Wonderful. We dilute the gypsum again and repeat the procedure on this side. Again, we try not to go to the front side so that the plaster does not close the mold on the other side. 
We get a solid gypsum cocoon. After it has completely hardened and cooled, we take a hammer and very gently tap from the ends and from the bottom in shape. There is a crack along the border where the plasticine was. You need to put a thin knife made of hard steel into it, or a wide screwdriver, and tap a little on top with a hammer so that the crack expands. 
After that, carefully push the mold apart and take out the model. 
We wash the resulting two halves with a brush from the remnants of clay and put them on the battery to dry. It takes a few days to dry for the form to be ready for use. 
The resulting form is not suitable for casting, but only for molding by the knock-out method, when clay is pressed in from the inside of the mold, with a layer of half a centimeter, and the bottom is glued separately to the slip. . But this is the simplest and fastest version, for getting a small run of the same figures. If you have any questions, I'll be happy to answer. If necessary, I can make a separate post about the warm-up. Good luck!
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 work should be presented to the exhibition in plaster, that is, in a more durable, long-lasting material.
Modeled products from clay, plasticine, wax have a number of disadvantages. So, for example, clay, drying up, cracks, falls off, decreases in volume. Plasticine and wax soften from elevated temperatures, melt and change their shape. Therefore, a sculpture fashioned from clay, plasticine, wax should be cast from another, more durable material - gypsum or cement. To do this, first of all, you need to make a draft form.
In the case when the fashioned thing - the original - must be made in several copies, you should make a special adhesive or lump form. This form will help us cast the required number of models. We will talk about the simplest production of draft 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 molded products. Gypsum is obtained from gypsum stone, which is fired at a temperature not exceeding 150 degrees. Gypsum is divided into medical, molding and plastering. Medical gypsum is the purest, finely ground and quick-setting. Molding plaster is almost as clean and finely ground, but with a slower setting time. The beginning of setting - after 4 minutes, and the end of setting - no later than 20 minutes. Plaster gypsum has a coarser grind.
What is the beginning and end of grasping? To prepare a gypsum solution (test), gypsum powder is mixed with water until the density of liquid sour cream. The beginning of setting is determined by when the gypsum solution begins to thicken, and the end of setting is when the gypsum becomes hard as a stone.
From long mixing, the gypsum mortar will “rejuvenate”, that is, it will not seize, and if it seizes, it will form many cracks and crumble from light pressure. Therefore, the gypsum solution must be prepared quickly for 0.5-1.5 minutes in order to use it before setting.
Gypsum has valuable properties, but it also has disadvantages. Valuable properties include the speed of setting and hardening, as well as the fact that the gypsum mortar during hardening increases in volume up to 1 percent. This gives him the opportunity to better penetrate into all the reliefs of the form. A significant disadvantage of gypsum is its ability to become warm, which adversely affects the adhesive forms, which melt quickly. In addition, gypsum warps.
In order to slow down the setting of gypsum, it is dissolved in glutinous water (3-4 tablespoons of liquid glue are added to a bucket of water), and in order to reduce warping, it is dissolved in milk of lime.
Dry gypsum products should not be in a through wind, this will reduce warping. Drying temperature should not exceed 60 degrees. From a higher temperature, gypsum begins to decompose, loses strength, and many cracks form on it. Gypsum is stored in a dry room. From long-term storage, even in a dry place, gypsum absorbs moisture from the air and stops setting.
Soaked gypsum is not suitable for work, as it does not set. It should be pointed out that gypsum products are stored in dry places; from dampness and water they are destroyed.
Molding plaster is sold in building materials stores, and medical plaster is sold in pharmacies.
Preparation of gypsum mortar. Gypsum mortar is prepared as follows: water is poured into the dishes and gypsum is gradually poured in, mixing it thoroughly. If gypsum is first poured into the dishes, and then water is added, lumps form in the solution. To prepare small portions of the solution, gypsum is diluted in rubber gypsum 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 closed in warm water.
For work, it is sometimes necessary to use a colored solution of gypsum, called a colored splash. In these cases, two tablespoons of some kind of paint are placed on a bucket of water: ocher, mummies, blue. Adding paint is no longer recommended, as this will reduce the strength of the gypsum.
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 lumpy cement molds. It turns out cement from a 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, withstand 1 square centimeter in compression from 200 to 600 kilograms.
The beginning of setting of cement - 30 minutes, the end of setting - 12 hours.
The product cast from cement should be kept in the mold for at least 5-7 days, and only after that it will be possible to split the mold. Store cement in a dry place. In addition to the usual gray-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 a cement mortar. For one part of cement, two or three parts of sand are taken and thoroughly mixed until a homogeneous mixture is obtained. Then the mixture is closed with water until the density of sour cream.
Glue preparation. For the manufacture of adhesive molds, bone and skin glue is used in the form of tiles or cereals. Glue in liquid form, the so-called galerta, is not suitable for making a mold. Glue is sold in building materials stores. Glue should be stored in a dry place, as it rots from dampness.
For the manufacture of adhesive molds, the adhesive mass is boiled. Before cooking, the glue tiles are split into pieces, placed in a bucket and poured 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 drain excess water from it. Then the glue is boiled in a metal bowl, but not directly on fire, but in the so-called water bath, that is, in an oil-cloth, which consists of two vessels inserted one into the other.
During the cooking process, the glue is thoroughly mixed, breaking up the resulting lumps. Bringing the glue to a boil is not recommended, because it loses its adhesive properties. If, after cooking, the glue turns out to be excessively thick, it is diluted with hot water, but not more than one glass of water per bucket of glue. To prevent the glue from rotting in the summer and eliminate the smell, 5-10 drops of vinegar essence are added to a bucket of glue mass.
The welded glue is cooled to 50-60 degrees before use so that it does not melt and wash off the lubricant applied to the model, and also does not stick to the model. Then the adhesive mass, having removed from it the film previously formed on the surface, is poured into a mold.
Adhesive molds after use are remelted. If the glue thickens during repeated remelting, it is diluted with water, and glycerin is added to it to maintain elasticity, based on a bucket of water - two glasses of glycerin.
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: 1 liter of hot water is poured into an iron or enamel bowl and 300-400 grams of alum are poured. The dishes are kept on fire until the alum dissolves and the solution boils. The resulting solution is cooled before use, otherwise hot alum can melt the adhesive form.
Talc- a thin, greasy to the touch powder obtained from the grinding of talc stone. It is used as a powder for degreasing adhesive molds before tanning. Sold in pharmacies or chemical stores.
Kerosene, soap, oil and stearin used to make lubricants. Lubricants are necessary in order to lubricate molds with them when casting products or to lubricate models before removing molds from them. Lubrication prevents the 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 making lubricants.
Recipe 1st. 1 kilogram of stearin melts with continuous stirring until it begins to bubble, that is, boil. After that, the dishes with molten stearin are removed from the fire 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 engine (burning) oil. The resulting mixture is poured into 1 kilogram of stearin previously melted and removed from the fire and mixed. After cooling, the lubricant is ready for use.
For lubrication of adhesive forms, petroleum jelly, garlic oil, soap suds and sunflower oil are sometimes used. The oil lays down in a thin layer, not covering the small pattern on the form.
Drying oil and varnishes. To make models and plaster molds waterproof and smooth, they are covered with drying oil or varnish.
Knowing the basic materials for molding and casting products, you need to get acquainted with tools and fixtures.
Tools and inventory for molding work
For stucco and molding work, a novice sculptor needs to have some more tools.
Blades for molding for the preparation of gypsum or cement mortar, it is necessary to have both large and small ones; they are easy 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 ground products. A cycle is a metal plate 1-1.5 mm thick, 50-70 mm wide and 100-150 mm long. One side of the cycle is smooth, the other has small teeth.
Pliers, chisel, hammer, saw, scissors used in molding.
Gypsum plasters are indispensable utensils for the preparation of various, and in particular gypsum, solutions. They are convenient in that the hardened gypsum mortar is easily removed from them from a light blow. Gypsum plasters do not crumple and do not prick, like other dishes. They resemble plaster cups made of black rubber and are sold in pharmacies and surgical instrument stores.
If it is not possible to purchase a plaster cast, then it can be made from a ball of any size by cutting it in half.
How to get a cast from a hand
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 give a good casting, which is necessary not only as a model for modeling, but also as a visual aid in the passage of anatomy.
Before removing the form, it is necessary to prepare at least half a bucket of soft clay. Then take a sheet of plywood or a planed board, that is, a stand, grease it with a thin layer of vegetable oil, petroleum jelly or lard. You should also lubricate the hand from which the form will be removed, but not very greasy. Then the hand is pressed against the plywood or board with the palm of your hand. The fingers of the hand, depending on the desire, can be closed or spread apart.
A thin layer (1 cm) of clay is applied to the hand and pressed tightly to the hand. Then a second layer of clay is placed on the hand, and it is also pressed tightly. Having put 2-3 layers of clay with a total thickness of 6-7 centimeters on the hand in this way, 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 applied to it is turned over so that the lining is at the bottom. Next, the stand, which is at the top, is removed from the hand, and the hand is carefully removed from the clay. The mold for casting one cast of the hand is ready.
The quality of the made form depends on the care of laying and the thickness of the layer of superimposed 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 mortar, and the cast impression is distorted.
Before casting, the mold should be well moistened with water, spraying it from the mouth or a spray bottle. When the form is ready, a gypsum solution is prepared (the solution should not be thicker than sour cream) so that it can completely fill the form. Gypsum 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 in the recesses. After 30-40 minutes, the gypsum will seize so much that it will be possible to carefully remove the clay from it. The castings should then be well cleaned and all defects corrected.
The cast of the hand can be cast in cement.
Now let's get acquainted with the manufacture of draft forms.
Making draft forms
Draft forms are removed exclusively from things molded from soft plastic materials: clay, plasticine or wax. Draft molds are rarely removed from the entire cast plaster model; most often, the mold breaks 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 as we will now analyze in two examples.
Making a draft form from embossed flat models. A draft form from flat models is made in the following order. A clay model intended for rough molding is well moistened with water. (Models molded from plasticine and wax are not subjected to any preparation before molding.) Then a colored plaster splash is diluted, the model is splashed with a layer no thicker than 5 mm and castles in the form of fungi are arranged on the splash. As soon as the splash sets, a supporting layer of white gypsum mortar is applied. After setting the gypsum mortar after about 40-60 minutes, the prepared form is slightly separated from the shield with a wedge, thereby forming a small gap. Water is poured into the gap in excess. Water soaks the clay, and the form 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 viewed, the remaining pieces of clay are selected from it using a wooden tool or a knife; after which the form is well washed with water, freeing it from possible smallest particles of clay that clog the sharpness of the picture. Washing the mold with water is best done with a syringe. Leaving a clay model in a rough form for a long time is not recommended, since dried clay is difficult to remove and wash out of the mold. The removed draft mold, after removing the clay from it, should be quickly used to cast the product from it. From long storage, the mold dries and warps, giving distorted castings. Thus, the shape is removed from flat models.
Making a draft form from three-dimensional models. A fashioned model, such as a jug, is well moistened with water until completely saturated. It is possible to remove the whole form from the jug, but it is not possible to choose clay from it. Therefore, the form must be made from 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 snugly against each other. It is best to insert them in such a way that each inserted plate overlaps the previous ones by 2-3 millimeters.
After inserting the plates and lubricating them with grease, they begin to manufacture 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 will be mowed down on the model from below, gradually moving up. Mushroom locks are made on the splash. After setting the gypsum mortar, they begin to apply a supporting layer - a thicker layer of white gypsum mortar.
After applying and setting the supporting layer and completely setting the gypsum, the plates are removed and arranged on the edges of the first half of the hole shape, that is, small, 5-10 millimeters, recesses, drilling them with a molding spatula or knife.
The holes are arranged in order to form bulges on the second half of the form. In general, this is called castle. The lock ensures the exact connection of the halves to each other and does not allow them to move during the casting of the model.
The edges of the mold with drilled holes are lubricated with grease. A rag or paper is removed from the model, the plaster crumbs that have fallen are removed and the second half of the mold is started.
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 fungal locks are arranged on it. A support layer is applied to the splash. As soon as the gypsum mortar hardens, proceed to the separation of the halves of the form.
Wedges are inserted into the seams between the halves of the form, 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 halves of the mold are easily removed from the model.
The made form is well cleaned of all pieces of clay, well saturated with water, tied and cast.
The casting should not be made massive, but the so-called hollow - hollow. The hollow model is lighter and requires less material. For casting, prepare a small amount of gypsum mortar, pour it into a mold tightly tied with ropes, and begin to turn the mold over in all directions, but so that the gypsum mortar does not spill out of the hole. Thus, the gypsum mortar doused, that is, covered, with a thin layer, the entire form. After the first round, the second and third ones are produced. For three rounds in the mold, a gypsum wall with a thickness of 2-5 centimeters is formed, which depends on the size of the model.
Casting a model from draft molds
There are two ways to prepare draft molds before casting models from them.
First way lies in the fact that the removed form is well saturated with water, that is, put it in water for 20-30 minutes. Then, the inside of the form taken out of the water is moistened with soapy water so that bubbles do not remain on the form, and the prepared gypsum solution is poured into the form.
Second way form preparation is not common, but more suitable for beginners. The made form is dried for 2-3 hours, then covered with alcohol varnish, after it dries, it is lubricated with grease and a gypsum solution is poured into it.
The second method has been sufficiently tested and has justified itself well.
Gypsum mortar is poured into the mold at 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 the various recesses of the mold. In this case, air pockets are formed that prevent the filling of the mold with gypsum mortar, and the cast model will be defective.
When the form is closed, consisting of two halves, such as, for example, a form from a vase, then both halves are lubricated with grease, connected together, tied tightly with a rope in two or three places, and first a small amount of gypsum mortar is poured into the form. The mold is turned in all directions so that the poured gypsum can cover the entire mold with a thin layer. After the first rolling, a second portion of the gypsum solution is prepared, poured into the mold and re-rolled. So gradually build up layers of gypsum, bringing its thickness to 2-5 centimeters.
Shape splitting
Two hours later, when the gypsum mortar hardens in the form, they begin to excavate the model. Since the model is not always taken out of the mold, the mold very often has to be smashed, that is, broken into small pieces. Splitting is carried out differently. In one case, chipping of the mold material is carried out using a chisel, chisel and hammer; in another case, the mold material is pierced with a thick knife. In either case, care must be taken not to damage the cast model. This is well facilitated by a colored splash, which warns that a model is located after 5 millimeters.
When the form is prepared according to the second method, splitting is very easy. If the form is removed from small things, then before splitting the surface of the form should be divided into small parts - pieces, not more than one centimeter, cutting strips, grooves along their edges with a knife or other tool. The splash should also be slightly incised and removed in separate pieces.
After splitting, the released model is corrected. If the plaster is not white enough, the model is rubbed with finely ground chalk or tooth powder.
Model clearing
On models cast from draft molds, there are some defects: roughness, insufficiently pronounced wrinkles, folds, lines, small shells (hollows) that require correction or, as they say, clearing.
First of all, small shells are covered with prepared gypsum mortar. Then, using a metal stack or a knife, they begin to clear the model. Rough places are smoothed with emery or glass sandpaper. After drying the product, for whiteness it can be rubbed with tooth powder using a brush.
Now let's get acquainted with the manufacture of adhesive molds.
Making glue molds
It is rarely possible to obtain several products from a draft mold, since it usually splits during the first casting.
In the case when it is necessary to cast several products, an adhesive mold is made. Let us analyze in more detail the manufacture of adhesive molds from different models.
Adhesive forms are made differently 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 covered with alcohol varnish once or twice before molding.
Making an adhesive mold in an open way. We need to make an adhesive form 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 than the model in width and length. The model is strengthened on a gypsum board, the cracks are smeared with gypsum 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, gypsum, tin. Its height is 40-45 millimeters, that is, 10-15 millimeters higher than the highest part of the model. So that the glue does not leak under the barrier, the places where it adjoins the gypsum board, that is, the seams, are smeared with clay, gypsum from the outside, and the model, the barrier and the plate are lubricated with grease from the inside. If the model has an openwork pattern, then excess grease from it is selected with a soft brush.
Then the model is poured to the edges of the barrier or slightly lower with the glue mass prepared and cooled to 50-60 degrees. A higher adhesive temperature is undesirable as it will wash away the grease. After the glue has hardened, after 18-20 hours, the barrier is removed, the adhesive mold is released from the model and the casting of products is started, pre-lubricating the mold with grease.
When casting products, the mold must be laid 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 form from deflections and distortions during casting, it is best to place it in a casing - a box, usually made of gypsum. The casing is made as follows: the sharp edges of the mold are cut from the outside with a knife and several small holes-pits 0.5 mm deep and 10-20 mm wide are cut out on its plane. The pits serve to form locks on the casing. Locks are further needed for proper installation of molds in the casing. Then they put a mold on the model, lubricate the surface and edges of the plate with grease, dilute the gypsum and coat the mold with a layer thickness of 10 millimeters.
To give the casing greater strength, thin draperies, wire or tow soaked in diluted gypsum are placed in the unset gypsum and the casing is again coated with diluted gypsum. Gypsum 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 made form is suitable for casting products, but it can quickly collapse. To protect the adhesive form from destruction, it is tanned. To do this, the front working side of the form is sprinkled with talc, the entire working side is lightly wiped with a dry soft brush, excess talc is removed and washed with a cooled solution of alum with a brush. The solution of alum accumulated in the recess is selected with a dry brush or cotton wool.
The tanned form is dried for about an hour and re-impregnated with alum. After the second impregnation, it is dried for about 5-6 hours with light ventilation. It must be remembered that without talcum powder, alum will not be absorbed into the oily surface of the form. Talc degreases the mold.
The casing must also be prepared, that is, dried and well coated with alcohol varnish (it is better to first proliferate and then varnish). The adhesive form should only be in a dry casing. This is necessary because from contact with the wet surface of the casing, it swells, increases in volume, changes its original shape and thereby distorts the casting. To facilitate the removal of the mold from the casing, it is 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 molds will be very thick and require a lot of glue. Therefore, they must be produced in a closed way.
Making a glue mold in a closed way. The manufacture of adhesive molds from high models is done in a different way. If you make a mold as indicated above, then in some places the adhesive layer will be very thick. The thick form is not elastic and not economical. When casting a thick mold, failure of an insufficiently strengthened material (product) and even the model from which it is made can occur. 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 casting products.
For example, you need to make a mold from an apple. To make this form, 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 mounted on a plate and fastened well with it. Then everything is covered with alcohol varnish. After that, the model is wrapped in a single layer of newsprint to protect it from clay contamination. 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 for locking. The locks eliminate the shift of the casing 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 chips, then the edges of the plate with the selected holes are lubricated with grease.
Since it is impossible to remove the whole 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 wetted with water. Then the plates are lubricated with grease and the gypsum solution is diluted. Gypsum mortar is smeared 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, tow.
As soon as the gypsum sets, 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. Casing thickness 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 now the model is covered with a casing, then a space is formed between the model and the inner side of the casing, obtained from the removed layer of clay. Liquid glue is poured into the resulting space, which, when solidified, forms 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 release air from the casing when pouring glue into it. If this is not done, the air, accumulated under the casing, will not allow the glue to fill the model and the mold will deteriorate. In addition, when the glue solidifies, it increases in volume (expands), its excess exits through these holes, subsequently forming locks.
The holes are drilled on 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. Glue is poured through these holes at the same time.
If glue is poured into one hole, then, passing through a large space, it will cool down on the way, it will not flood the entire model, and this will lead to marriage. Holes are recommended to be drilled 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 place than in places with a relief pattern.
Having drilled all the holes in the casing, its inside is coated twice with alcohol varnish; the model of the edge of the plate and the inside of the casing are well lubricated with grease. The casing is additionally sprinkled with talcum grease and the model is covered with it so that the locks fall into place. So that the glue does not leak out of the seams during pouring, the joints of the casing with the plate are coated with clay or gypsum. The plate is tied to the casing with ropes or some heavy load is placed on the casing. This is done so that the glue, expanding, does not lift the casing during setting, but, on the contrary, presses on the model, enters all 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 of roofing iron, cardboard or clay. The funnel is installed on the casing, and the junction on the outside is smeared with clay or gypsum. Lubricate the inside of the funnel with grease and pour glue.
Glue is poured through a funnel, thus filling the empty space between the model and the casing. In those cases when glue begins to flow 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 pressure of the glue in the mold, and there will be no bubbles and shells on the surface of the funnel that reduce the quality of the mold. After the glue has hardened, the casing is removed from the adhesive 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 with a sharp knife into two parts. It is desirable to cut along the seam of the casing. Then the glue mold is degreased, tanned, dried, the casing is varnished - and it is ready for casting products from it.
A closed mold is more durable because the adhesive becomes denser and the pattern is sharper.
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 usually made of two parts.
Thus, we got acquainted with the manufacture of adhesive molds from flat and three-dimensional models. But what to do when there is no glue, but you need to multiply, that is, to cast several castings from a plaster model molded and cast from a draft mold? It turns out that, in addition to the adhesive form, there is a so-called lumpy, or plaster, form. Thus, when there is no glue, but there is gypsum, a plaster mold can be made.
It must be pointed out that the manufacture of a plaster mold is much more difficult than an adhesive mold, since a plaster or lump mold rarely consists of one or two pieces. Most often it consists of several pieces.
We will analyze the production of a lump form on the simplest models. It should be pointed out that lump forms are made only from solid models made of plaster, stone, wood, metal. Gypsum and wooden models must be fixed, that is, coated twice with alcohol varnish.
In this case, we will talk about the manufacture of the simplest lumpy forms. For example, we have an apple model. From this model it is necessary to make a lump mold for casting several products.
The simplest form may consist of two pieces: the first and second, or the lower and upper. Before proceeding with the manufacture of the mold, the model must be prepared.
The gypsum model is first of all coated once or twice with alcohol varnish and, after the varnish has dried, lubricated with grease.
Before molding, the model should be divided in height into two parts so that halves of the molds can be easily removed from them. If the halves are wedged, castings cannot be removed from them without damaging 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.
Production of lumpy molds
After that, the gypsum mortar is diluted and the model is splashed with a thin layer. A second layer is applied to the first unset layer of gypsum, smoothing it well. The thickness of the gypsum layers or mold walls should be 20-25 millimeters.
As soon as the applied gypsum sets, and this will happen in 40-60 minutes, the model is removed from the mold, the edges of the mold are leveled, that is, they are cut with a knife and two or three holes are drilled on them. Holes are needed so that another piece can form locks in them.
Then the piece is well swept from plaster crumbs with a brush, the model is placed in the mold, the edges of the mold and the model are lubricated with grease, and the laying or making of the second piece is started. The second piece is laid in the same way as the first: that is, a gypsum mortar is prepared, it is applied to the model in a thin layer, a second layer of gypsum is applied to the thin layer. As soon as the gypsum has set well, the entire outer surface of the mold is cut off and the pieces are separated. The made form is suitable for casting of hollow products.
Before casting, the inside of the two pieces of the mold is lubricated with grease. Then a portion of the gypsum mortar is prepared. Gypsum fills only one half of the mold and closes it with the second half, while turning in different directions. The solution pours 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 after casting should be dried, 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, castings should be removed from the mold no later than 25-30 minutes after pouring the mold with gypsum. Cement products cannot be cast in adhesive molds, but only in lumps. It is necessary to withstand castings for 3-5 days.
Manufacturing of various tools and fixtures
As we have already said, various tools and devices are needed for sculpting. Some tools and devices can easily be made by members of the "Skilled Hands" circle, such as stacks, coasters, easels, etc.
Stacks. Wooden stacks are cut from dry wood with a sharp knife or chisel. Having processed 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, letting it dry after that for 2-3 days.
To cut off excess clay and cut out recessed places, stacks with metal tips. Produce wooden cuttings. Then they take a 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, at the bottom of which holes are pierced with an awl or nail. Wire hooks are inserted into these holes and twisted with a thin wire. The tips are flattened with a hammer. At the ends of some tips, teeth are sawn with a file. With their help, dried clay is cut better.
It is better to make stacks three to five, of different sizes and shapes.
Used for molding and metal stacks, which can be made from copper, aluminum or iron wire with a hammer and file.
metal compass you can buy in a store, and a wooden one is easy to make yourself. Usually compasses consist of two legs with sharp ends connected by a screw. Making a compass is not particularly difficult. They take plywood 5 millimeters thick, from which planks are cut, but it is better to 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 down already. The strips are folded together, a hole is drilled at the top, where a wing screw or a thin bolt with a nut is inserted. If there are no such screws, the planks can simply be connected with an ordinary screw, which is turned when the legs are loosened. On the lower ends of the legs, thin nails should be inserted or iron tips made of roofing iron and tin should be nailed; in the figure (Fig. 248 (5) the device of the compass is shown.
Compasses-pantographs are metal and wooden; both are sold in stores, but can be easily made. How to make a pantograph compass ourselves, we told 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 of 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 must move freely. Then they take a piece of wood with a cross section of 2-3 centimeters, 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, of such a size that the pin can freely enter 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 the pin, we can assume that it is ready for measurement. The legs and the pin move along the guide, and they have to be installed in the right places motionlessly. To fix 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, or you can make your own from horsehair or bristles. They are made like this: they take a bundle of hair or bristles, align their ends and, on one side, tie them in one or two places with strong twine, after which they cut one end, make a wooden handle with one pointed end and put a bundle of hair on it or fix it into a metal frame.
syringe are made like this. They take a piece of a metal tube 30-40 centimeters long, with an inner diameter of 2 to 4 centimeters. The tube that is rusty inside must be cleaned by wrapping a rag on a stick, moisten it with water, sprinkle 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 poured with lead 2-3 centimeters thick or plugged with a wooden plug, 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 taken thicker). The length of the piston is 5-10 centimeters longer than the diameter of the tube. At one end, a wooden sleeve is reinforced with a diameter of 5-6 millimeters smaller than the inner diameter of the tube. The sleeve is wrapped with linen or a rag, but so that it fits tightly into the tube. The winding is lubricated with machine oil, grease or petroleum jelly. A pen is made at the other end of the rod, and the syringe is considered ready. For a smooth piston stroke at the second end, it is advisable to insert a second plug, making a hole in it along the diameter of the rod.
Types of plaster molds
Single piece forms. Gypsum molds are single and multi-piece. First, consider the simplest forms in the form of a single monolithic piece. They can be made in several ways.
First way. We have a model of a relief panel measuring 20 x 20 cm, made of raw clay and placed on a sheet of paper or piece of cloth. To make a shape, we will transfer the model to a piece of glass or plastic, which is larger in size than the panel. Let's build a side fence 2–3 cm thick and also 2–3 cm higher than the highest protruding point on the panel. The fence can be a tape of cardboard, clay, plasticine or wooden planks. So that it does not move apart when pouring gypsum, fix it from the outside (support it) and close all the cracks. Raw clay product does not need to be lubricated.
We prepare a solution. First, sift the gypsum powder through a thick sieve. Take a rubber cup (half of a large rubber ball) and pour ordinary water into it. Now we will pour enough sifted gypsum with a spatula or spoon so that a small cone is formed above the water, which in 2-3 minutes will disperse in the water. Only after that, with a stick, carefully and smoothly, will we begin to mix it (so as not to capture air into the solution) for 2-3 minutes, depending on the quality of the gypsum. After stirring, a little foam forms on the surface of the liquid, which should be removed. We slightly fill the panel with gypsum mortar, straightening it with a soft brush so as to completely close and destroy air bubbles, and then pour out the remaining solution.
It is not recommended to add new portions of gypsum to the finished solution and mix it additionally. Gypsum mortar hardens quickly, but within 12-15 minutes it is still quite soft and easy to process. Completely solution hardens in 25-30 minutes. When the surface of the hardened gypsum warms up, it can be turned over and carefully, so as not to damage the shape, pull out the clay panel.
We have received a one-piece form. We clean the edges of its irregularities with a knife and leave to dry. Dry at room temperature, as sudden heat can destroy the gypsum. When it dries completely, it will become lighter and lighter. Then a layer of clay can be filled into the mold. After 30–40 minutes, carefully removing the form, we will get a panel.
Second way. We have a model of the same panel, but made of dried clay. In this case, it is impossible to fill the model with liquid gypsum to make a mold. Since there is water in the gypsum mortar, which will soak the clay, which, in turn, will expand and destroy the form, you must first isolate the clay from the gypsum.
The simplest insulation will be ordinary laundry soap dissolved to a state of sour cream. This solution is used to lubricate the model before casting with plaster.
Better yet, add transformer, machine or vegetable oil to the soap solution at the rate of 250 grams of one tablespoon. Some experts rub the model separately: first with oil, and then with soap suds. In addition to oil, a primer is needed - to avoid soaking the model. Prime the dried panel 2-3 times with hot or cold drying oil - this is the simplest primer. But the best primer is diluted alcohol with lye (25% lye + 75% alcohol). Gypsum is glued with the same solution, but thick. When the primer dries (after a few days), you can start molding, after lubricating the clay panel, which is the model.
Third way. If it is necessary that the model be preserved for a long time, then it must be transferred to plaster.
To do this, the first plaster mold is cast, primed from the inside, lubricated and poured with a solution. They get the same panel, only plaster. It can be tweaked and improved. Therefore, the panels are primed and dried. Here is the finished model. Using it, you can make many forms. Note that before each pouring with plaster, it is imperative to cover the model with a soapy solution that does not form greasy spots on the inside of the mold. Stains make it difficult for the clay to separate from the plaster, which can ruin wet prints. There is a solution that washes away such stains. This is 3% soda ash, as well as copper sulfate.
Multi-piece molds it is more difficult to make than single-piece ones. Consider this process using the example of making a mold from a pottery, already fired jug. We prime it and use it as a model. Since the jug is not cone-shaped, you will have to divide it vertically exactly into two halves, which means that the shape will be two-piece. To do this, we use a compass, a pencil and a triangle (Fig. 60).
You can divide the model in another way (Fig. 61).
Find the center of the bottom and top with a compass. We mark it with a dot on the bottom. Lay the pitcher horizontally on the table, securing it with pieces of clay on both sides. Let's check the horizontalness by measuring the distance from the center of the bottom and the center of the top to the plane of the table. If they are the same, then the model is in a horizontal position. With the same step of the compass, we draw a horizontal line on both sides of the jug: one leg of the compass is on the surface of the table, the other, with a pencil, is on the side of the jug. We unite the ends of the lines through a point in the center of the bottom.
We make a box-fence (can be collapsible) from boards so that the distance from three sides of the model to the box is approximately 3-4 cm. The height of the fence should also be several centimeters more than the highest point of the model. Its top - and we have this neck - is pressed to the inside of the box. The space created on three sides between the model and the box, from the surface of the table to the separation line, will be filled with clay or plasticine (at the same time, you need to check if the bottom has sagged inward). Level the clay and grease the remaining half of the model with an insulating solution. Prepare a fresh plaster solution, pour the model on top and smooth the surface flush with the box.
When the plaster hardens, we will dismantle the fence and free the model from clay. We will pull out the model, holding it with one hand and lightly tapping with a wooden mallet on the wall of the hardened plaster. We received one piece of the mold. We clean and level it from the side where the gypsum touched the clay. In the same place, we cut out cone-shaped nests for locks with a knife. With the help of these locks, the two halves will exactly match and not move (Fig. 62).
Insert the model into the already made piece of the mold with the same side. Let's put it back on the table so that it is on top and the plaster is on the bottom. Let's place the box, as in the previous time, grease the jug and plaster over the entire surface, where it touches the new, other, half of the mold. Prepare a fresh gypsum solution and fill the box to the top. When the gypsum hardens, remove the box and, in the assembled state of the two halves, clean the entire mold as one. Tap them apart and pull out the model. The two-piece form is ready, it can be connected using rings cut from old rubber tubes, car tires. They hold the parts well.
In addition to the jug, thanks to the two-piece form, other ceramic products can also be made.
Lay the model flat on the table. Then rotate, marking by eye a line that will divide it into left and right parts (top-bottom). Place the model upside down and cover with clay up to the dividing line, making a box. The height of the walls of the box should be a few centimeters higher than the end point of the bottom. Lubricate the pre-primed model with soapy water before pouring, prepare a plaster solution and fill the entire box. After curing, disassemble the box and remove the model. Having made the second part, we clean the entire form (Fig. 63).
To make more complex models, multi-piece molds are used. Asymmetric models need to be well examined, dividing lines should be outlined, and the order in which the pieces should be made should be considered. The technology remains the same.
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