Wedgwood photo

The vast majority of ceramic wares sold commercially today are cast in plaster molds.Only in expensive gift shops and art studios will you find original, one-of-a-kind, handmade pottery or sculpture for sale.Just as the assembly line makes it possible to manufacture automobiles in large quantity and at a popular price, so the mold makes it possible for the ceramist to produce multiple, inexpensive copies of a design.

There are all kinds of molds on the mar­ket today, which for the most part can be purchased by the hobbyist at reasonable cost.Most of these are more or less mass-produced by professional ceramists who have created the original model.It is pos­sible for you to buy a mold for virtually any type of ceramic ware you would like to turn out in your workshop.

However, you will find it surprisingly easy—and probably far more satisfying— to make your own molds, either of your own creations or of any other objects you feel would be worthwhile reproducing in clay.The model itself may be a ceramic piece; it may be made of plasticine, wood, glass or anything else.Remember, though, that a model made of thin and delicate glass is liable to crack when the plaster starts to set and becomes hot.

The simplest and most primitive type of molds can be made from gourds, shells or baskets.Known as press-molds, these are capable of producing clay likenesses of themselves which can be imaginatively decorated.All you must do is powder the inside surface to prevent the clay from sticking, press in some plastic clay and smooth it with a damp cloth or sponge be­fore it dries.When the clay has sufficiently hardened it can be shaken out gently.

Molds can also be made of clay which is fired at a low temperature so that the body remains porous.Such one-piece molds can be formed simply by impressing the model in them, or by working the clay around the model to the same shape.Such molds are capable of giving a sharper impression and finer detail than those made of plaster.

The most practical mold, however, is made of plaster.There are two ways molds are used.If plastic clay is used then you must have a press-mold.Generally speak­ing, however, molds are utilized for cast­ing objects with slip.These are called pour-molds.Any press-mold can also be used for casting, and, in some instances, the reverse is true.

Let's assume you'd like to make a plaster mold of a water glass.Besides the glass you are using as the model, you'll need a small box, a brush, some liquid soap, a scraper and a medium-size bag of plaster.The box is used as a retaining wall for the plaster when it is poured and should be about one and one-half times as high as the model.

First step is to brush the outside sur­face and the top rim of the glass gener­ously with the liquid soap.This procedure is called sizing.Now turn the model up­side down in the bottom of the box.It is often a good idea to slide the glass back and forth a few times until a suction is created.It is necessary to size the item being molded in order to prevent the model from sticking to the plaster after it has set.

Mix a solution of potter's plaster and water to the consistency of thick cream.The more water you use the more porous your completed mold will be.Hence it will absorb more water and speed up the cast­ings you will make in the finished mold.However, the mold will also be more fragile.Therefore it is better not to make your plaster mixture too liquid.One part water to two parts plaster is the rule of thumb.

Pour the plaster into the box.When it is full and the plaster has completely cov­ered the glass, give the box a few smart raps.This will release any air bubbles which may have formed during the pour­ing.Once the plaster has started to set do not disturb it on any account, or it may not set at all.When the plaster has properly hardened, remove the box from around it.Turn the mold over and pick out the glass, which can be removed without difficulty because of the soap separator.

The final step in making any plaster mold is to chamfer the edges.This is the round­ing off of all edges except those formed by the model.Take your scraper and trim off about one-fourth inch from the angles formed by any two outside faces of the mold.This is done so there will be no sharp angles or corners to break or chip.

You now have your first mold.Basically it is a casting mold, into which you will pour slip.(Instructions on how to use such a one-piece mold are given in the follow­ing chapter.)

Always store molds upon wooden sticks to permit air circulation around them; use them' to stack.

Wedgwood with molded design is made by cast­ing; many such shapes are easily made with molds.

Above are a two-piece and a three-piece mold with the greenware cast from them—plate, flower vase.

If you had no trouble with this project, you can begin making many similar one-piece molds.For example, to make a sim­ple press-mold, fill the box with plaster again and shake or vibrate to eliminate air bubbles.When the plaster has begun to set, but before it has become hard, push a button or ornament into it, making certain the back does not go below the surface of the plaster.Be sure also that the model has been liberally doused with liquid soap.When the plaster has set, you will have no difficulty removing the ornament.

Let the plaster dry for several days, then press a piece of plastic clay into the inden­tation left by the model, the same as you did with the aforementioned gourd- and shell-molds.Smooth the outside surface.Wait a few minutes for the plaster of the mold to absorb the moisture in the clay.This will cause the clay to shrink slightly, so that if you invert the mold and tap it gently, the clay reproduction will fall out.

A large variety of things can be cast in one-piece molds.However, a mold of two or more pieces is often required.The num­ber of sections required in a mold depends entirely upon the number of undercuts in the model.An undercut is exactly what it sounds like—some part of the model which forms an angle that cannot be simply lifted out of a one-piece mold.The handle of a vase, for example, is a common undercut which must be cast in a two-piece mold.The separate sections of the mold can be individually removed, thus overcoming this obstacle.

In making your two-piece molds, let's as­sume you want to reproduce a milk pitcher.

Your first problem is to divide the pitcher-model into two equal parts vertically.This can be accomplished by drawing a thin dividing line along the outside vertical cen­ter.Dark watercolor paint and a fine brush are ideal for this.You may also use a thin glass-marking crayon.If a pencil is used, care must be exercised that you do not damage the surface of the pitcher with the sharp point.The line should bisect the handle as well as the main body of the pitcher.

Stop up the mouth of the vessel with a solid wad of clay, which should project two inches or so beyond the opening.This is called the spare.When the mold is made, the spare will cause a funnel-shaped open­ing at the top of the mold, through which you will pour the liquid slip with which you cast your ware.

The purpose of the spare is to insure that the top edge of the cast ware will be the same thickness as the rest of the piece, for slip settles into the mold as it dries and shrinks a little.If there were no spare to hold a small amount of extra slip at the beginning, the top edge of the model being cast would become irregular in shape and thinner than the rest of the body.

After you have completed the spare, im­bed the pitcher in a block of soft clay up to the dividing line.Allow the spare, or clay stopper, to project slightly beyond the edge of this clay cradle.Smooth off the surface of the clay precisely level with the divid­ing line.If the clay bed falls below the centerline in places, build it up with surplus clay.Exactly half of the pitcher should be imbedded in the clay cradle; half should protrude above the surface of the cradle.

Left, to make your own mold start on flat surface spread with newspapers.For small item, a bak­ing tin acts as form: otherwise make a wooden form.Items needed: tincture of green soap, brush, pencil, plastic clay, a wire-cutting tool, potter's plaster (to which you add water, 50% by weight).

Next you must build retaining, or re­straining, walls around the block in which the pitcher is half-buried.The box-shaped form, of course, has no bottom or top.It should be at least two inches higher than the uppermost surface of the exposed half of the pitcher.You may construct the re­straining walls of wood, linoleum, rubber or asphalt tile, or stiff cardboard.The smoother the walls, the smoother will be the exterior surfaces of the finished mold.

On your worktable now you should have a block of clay containing the half-im­bedded pitcher, securely enclosed on four sides by the restraining walls, which should be tied or banded together.About an inch in, diagonally from each corner of the clay block, gouge out a semicircular hole.These four holes will be much like those a large marble would make if it had been pressed into the flat surface of the clay.Make each hole about three-fourths of an inch in diameter.

Using your liquid-soap separator, thoroughly cover the inside surfaces of the restraining walls.Then apply the soap gen­erously to the pitcher itself.Prepare your plaster and pour to the very top of your wall form.When the plaster has set, you will have half of your two-piece mold.

Remove the walls and the clay bed from the model.Do not separate the pitcher from the plaster, nor remove the spare from the pitcher's mouth.Smooth all the plaster surfaces as much as possible, plac­ing the mold so that the protruding portion of the pitcher is facing upward.

Construct four walls around the mold as you did before.The walls that were used for pouring the first section can con­veniently be used again.Brush the entire top surface of the plaster with liquid soap, including the naked half of the pitcher.Many coats will be required on the plaster to make it sufficiently water-repellent.

The first section of the mold will have four raised hemispheres in the corners, where you gouged out the holes in the orig­inal clay block.When you pour in the plaster for the second section, indentations procedure is much like that for producing the pitcher mold described above.You begin by drawing the dividing lines on the model.

With the more complicated form of the squirrel, this will be a bit more difficult than it was with the pitcher.A simple way to find where the lines should be drawn is to look at the animal full face.The ex­treme edge of the silhouette is where you should draw the vertical lines on both sides of the squirrel's body.

Lay the animal on its stomach, so the lines are now horizontal.You can see why its tail necessitates your pouring two molds.One section over the tail could not be drawn loose.But if two sections are formed for the back, they could be drawn loose by pulling to each side.Thus, you must locate the vertical dividing line for the figurine's back and tail.This can be done by standing the squirrel sideways and looking directly at the silhouette of the profile.Again, the edge of the sil­houette that you can barely see is where the line should be drawn.Begin at the highest point of the head, go directly down the back, up along the front of its tail, over the high point, and down the back of the tail.

When you have completed drawing the dividing lines, you are ready to make the first section of the mold.It's usually best to make the mold of the front of the figurine will be formed by each of these protrusions, forming a kind of lock that will hold both halves of the mold together securely and in the correct position when the ware is being cast.In other words, there is a male form and a female form with every two-piece mold.

Take half-mold you made and put clay strips all around.Gouge out two key notches for fitting.

Make another clay spare for top of vase.Tighten clay around.Next step is to soap vase as before.

Once again mix the plaster as you did the first time, add it to the vase for second half of mold.

When plaster has hardened, remove second half of mold from pan, and now you have complete mold.

Alter you've smoothed surface of clay evenly around vase, you are ready to paint interior and vase with green soap.This will prevent plaster from sticking.Now mix plaster slowly, as shown at right; too fast mixing will make air bubbles.Mold here is being made by author's son, George.

After the second pouring has hardened, remove the walls.The right time to take the two sections of the mold apart is when the plaster has reached its maximum heat.Don't let the plaster get cold and then try to separate the sections.If you have dif­ficulty, use a spatula or a dull round-ended knife and gently pry the sections free.

Remove the pitcher.Take away the spare.Chamfer all the outside edges of both pieces to reduce the danger of chip­ping.You should not attempt to cast any­thing in the new mold until it has had enough time to dry thoroughly.Several days is the minimum waiting period for the plaster to develop sufficient porosity to function properly.

Once you have mastered the technique of making one- and two-piece molds, there are literally thousands of ceramic items you will be able to cast in your workshop.For molding figurines, however, you will generally need a three- or four-piece mold.The extra sections are necessary to take care of the more complex shape.

Suppose you desired to make a mold of a squirrel figurine, sitting upright, its bushy tail behind.You may, if you wish, make individual molds of the squirrel's body and the squirrel's tail, cast them sep­arately and then glue them together with slip before firing.

Or, you could make a single four-piece mold in which you can cast the entire figu­rine at one time.You will need one sec­tion for the front, and two for the back.In addition, another section should be made of the bottom of the squirrel so that the figurine-to-be will have a clay base.This is not absolutely necessary, but the base of the figure looks more finished if it is made of clay with a hole left near the center for casting purposes.

To make such a four-piece mold, the first, in order to reduce the chances of damaging the features.

Holding the squirrel with its face to the ceiling, build up around him to the divid­ing lines a cradle of soft clay.The clay surface should curve with the irregulari­ties in the dividing lines along the animal's sides.The feet should be flush with the edge of the clay cradle, but there should be at least an inch to spare on the other three sides of the body.Now proceed as you did when you made your two-piece pitcher mold; build restraining walls, apply soap separator and pour the plaster.Do not, however, gouge out corner holes in the clay bed as you did before.

As soon as the plaster has set, remove the walls and the clay cradle.Smooth the surface of the plaster with sandpaper.With metal plaster tools, cut notches into the plaster wall on each side of the squirrel, which is still imbedded in the plaster.Be­cause of the irregular shape of the model, some parts of the wall will be wider than others.Put your notches in the widest spaces.

Preparatory to making the second sec­tion, thoroughly brush the squirrel and the upper plaster surface with several coats of liquid soap.Place the animal on its side and build another soft clay cradle up to the dividing line drawn from the top of the head, down the back and over the tail.

Construct the restraining walls again to enclose this section and pour the plaster.As soon as it has set, remove the walls and the clay bed, but do not separate the model or the two sections of the mold.Smooth the new plaster surfaces with care and cut two notches in the new outside wall.

Apply several more coats of liquid soap, especially to the newly formed plaster sur­faces.Enclose the mold with restraining walls and pour the third section.When the plaster has set, remove the walls.Scrape the mold until it is neat and rec­tangular in shape.Turn the mold so the bottom side of the squirrel is up, and cut notches in two of the four walls.

You are now ready to make the fourth and final section.Cover the entire bottom surface of the plaster mold, as well as the base of the squirrel model, with ample brushings of liquid soap.It must be abso­lutely water-repellent.

Fashion a clay form in the shape of a funnel.Size, of course, depends upon how big the figurine is.If it's about five inches tall, then the funnel should be about two inches in diameter at the top and three-fourths inch diameter at the bottom.Place this over the center of the base of the squirrel to form the hole for casting.In the completed mold, this will be the hole into which you pour the slip.

Put up the restraining walls again and pour in the plaster.Remove the walls as soon as the plaster reaches its maximum heat.Then carefully open up the sections of the mold and remove the squirrel model.The notches you have cut in the plaster walls will fit together and serve as a key; each piece of the mold will fit only in its proper place when you start casting re­productions of the squirrel figurine.

Finally, chamfer the edges and dry thoroughly for several days before using the mold.With the know-how and prac­tical experience you've gained in making these molds, you should be able to make all but the most complicated types of molds in your own workshop.•

Slipcasting mold and bowl made from it are shown below.To right of bowl is ash-tray drape mold.

Another type of mold is the press mold held in hand below.This is simple method of making tile.

Photos from "Craftsmanship in Clay"

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