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Pottery Tips and TechniquesCreating Plaster Molds |
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I think plaster molds are the neatest things since sliced bread! You can pour plaster into a plaster mold to make a reverse mold, but you will definitely need mold release agent like liguid hand soap or non stick cooking spray or the plaster will stick. Plaster Cast Over Wet ClayYou don not need to use mold release on leather hard clay, prior to pouring the plaster.Carving Press Molds And Sprig MoldsPress molds usually consist of two pieces, each one having a relatively shallow impression of the item to be reproduced, surrounded by a trough into which any excess clay will be squeezed. Soft clay is placed into the impression in one half of the mold, then the other half is placed over it and the two squeezed or pressed tightly together. Press molds are quite often used for making pottery stamps ( to sign your art with), small ornaments, knobs and handles.Sprig molds are one-piece molds with shallow impressions, from which flat-backed, shallow castings are produced when a piece of clay is forced into the impression. The process of attaching the items from these molds to greenware is called "sprigging." The raised decoration on the familiar Wedgwood pieces are formed in sprig molds. Stamps and sprigs are really nice when used around a border or across multiple pieces of pottery or ceramics to achieve a repetitive design element. Poured Press MoldsAnother way to use plaster is to pour it into and around any object of your choice.Every time you pour, you will be making a reverse of the object you are pouring into or around. You can pour plaster on top of leatherhard clay. You will need to build a box frame large enough to hold your pottery piece and the plaster surrounding it. Using a roll of clay on all the seems, so that the plaster does not run out. Pour the plaster over the object. When pouring these types of molds, it is best to pour enough slip, so that your object is covered with a couple inches of plaster and has at least 2 inches of plaster around the outside. Hump And Slump MoldsIt is very useful to have molds that you can put slabs of clay over such as, hump molds or into slump molds for making platters and dishes.The benefit of working with a hump mold is you have access to the bottom of the clay for adding feet or decorating the back side. But, the down side is you have to remove the item before it is completely dry to attach any feet or work on the back side and it could collapse if it is taken out when it is too wet. Plaster makes great slump and hump molds because the clay won't stick. They can be made in a variety of ways. Be sure to use mold release on the object before pouring the plaster. You can pour plaster into objects you have around the house such as bowls and platters to make a hump mold. You can make your own shape out of clay by pressing balls of clay together in whatever shape you want. You could even make a rectangular casserole dish. A wooden paddle is useful for getting your clay close to the right shape. Then you cut a pattern out of cardboard which is the profile of the cross section you want. For a rectangular shape, you will need two pieces of cardboard, one for each direction. Pull this cardboard across the soft clay pieces to finalize the shape. Once this shape is made, burnish the edges so they are very smooth and then build a moat around it and fill with plaster. A round hump mold can be made out of clay on the potters wheel. Just center a lump of clay, use a rib or trimming tool make and smooth the shape. Then plaster can be poured around this to create a slump mold. Once you have a slump mold, you can then pour plaster into it to make a hump mold. Because it is plaster on plaster, be sure and use a release agent. You can make a slump mold from a hump mold by sitting the hump mold on the floor, making a frame around it and filling the space with plaster. You can make a nice slump mold by centering a tub of plaster in its liquid stage on your wheel and spinning it at constant speed till it sets up. Spinning a liquid in a tub produces a parabolic surface and the faster it spins, the deeper the curvature is. Watch out, if the speed is fast enough for the edge of the parabola to climb over the edge it will spill plaster all over the place! Try this with a tub of water until you are sure you won't spill it over the edges. Modifying MoldsRound Bottom MoldYou can modify the shape of a plaster mold after it has been made and before it is dry.If you want a rounded bottom hump mold, but only have mixing bowls with flat bottoms, this is what you do. Center and trim the bottom into a round shape with a trimming tool. Mushroom MoldIt is helpful to have hump molds up off the work surface so your clay can extend past the edge.This also makes it easier to trim the bottom if you want the clay even with the plaster surface. One way to do this, is by adding a foot to the hump mold, creating a mushroom mold. You can take a piece of cardboard tubing that posters come in and imbed it into the backside of the plaster before it sets. A more common way is to make a plaster foot. Before the mold has set, scratch and roughen up the middle of the plaster and take a thick coil of clay and place it where you want the foot. ’t be tipsy. Fill the coil with more plaster and let it set. Other DetailsYou always have to remember that clay shrinks, so your plaster molds should be about 10% larger than the desired size of your final piece.Check to see what kind of clay you are using, because they all shrink at a different rate. You can use cheesecloth between the plaster mold and the clay to help with the removal, especially as the plaster starts to get wet. Let air circulate around your plaster mold as it dries. You can put it on top of your kiln or over a radiator to speed drying, but don't set it right down on the kiln lid, keep it elevated so it dries evenly.
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All About Clay The best way of starting out is to take a few lessons. You will probably waste quite a bit in materials when you first get started. Figuring out how to truly make handmade pottery correctly and shape into what you want it to be can be quite an ordeal. The different tools that a normal shop will have can be fun to try. You will soon see which ones you like to use the most and then when you are ready you will know which ones to buy. When you get all set up, just enjoy the
hobby and have fun at it. Some people get pretty
serious and start selling their creations at craft
fairs and small stores, but others just like
to create items for themselves, relatives, and
friends. Whichever kind of handmade pottery you
desire to endeavor, enjoy the hobby and have
fun doing it. |
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