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Pottery Tips and TechniquesMixing and Pouring Ceramic Plaster |
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Plaster of paris is very useful for making molds. MixingHere is one method that works quite well.Make a frame for your mold. Buy a bag of plaster. Pottery Plaster #1 is best because the particle sizes are small and will capture detail the best. But if you can't get this, normal Plaster of Paris will work. Always put on a dust particle mask when mixing plaster. Add water to a bucket. It should be between cool and room temperature. You will learn through trial and error how much water to use, but most people tend to underestimate the amount of water needed. If you want to avoid cleanup, line your bucket with a plastic bag, then discard the whole thing at the end. Using a cup or scoop, start adding plaster to the water. Sprinkle the plaster out evenly over the whole surface of the water. You don't have to be in a big hurry, but don't work too slowly or the plaster will start to set. Some people prefer to sift the plaster into the water. The plaster will sit on the surface of the water briefly before disappearing beneath the surface. This is called slaking. Keep slowly adding plaster, sprinkling it in the same manner. When you add plaster and can count to 5 before it disappears, you have enough. Let it sit for 1 to 2 minutes to wet the plaster particles, this helps reduce air bubbles. Start mixing. You want to make sure that you aren't adding air to your plaster or you will get bubbles which will cause problems later. If you use an electric mixer make sure to keep the blade deep in the plaster. You can just take your hand, a glove is useful, and place it at the bottom of the bucket and slowly move your hand back and forth across the bottom of the bucket. This slowly wets all the particles. When you can draw a line in the plaster and it doesn't immediately flatten back out, the plaster is ready to pour. PouringThe main thing in pouring the plaster is to avoid introducing air pockets, particularly on the surface that you are going to be using.Pour slowly. Some people allow the stream of plaster to run off the palm of their hand, slowing it down. It will help to put a thin coating all over the surface and allow it to set a little before pouring the final amount necessary for the mold. If air bubbles come to the top of the thin surface, they will be away from the actual surface you will be using. This is especially useful if you are pouring upside down, which means you will use the bottom surface of the mold you are pouring.) After pouring, pick up your container and softly tap it on the table or the floor. If it is too big, tap the edges and shake from side to side. You are trying to get air bubbles to the surface. Here is a neat trick. Use rubbing or denatured alcohol in a spray bottle. When the plaster mixing is almost complete, spray a couple bursts into the plaster. This breaks down the surface tension of bubbles on top and they disappear. After pouring you can repeat this when there are bubbles that have risen to the top of the mold. This is really useful if you will be using the top surface of the mold you are pouring. Smooth the top of your plaster item with a rib or something like that and let it set. Clean your bucket and tools at this time. If you are pouring a large mold or for some reason didn't mix enough plaster in the first batch, immediately start mixing the second batch. When it is ready you can pour it over the existing plaster. Scratch crisscross lines into the top of the first layer before pouring the second layer to help them adhere together. There will be a point where the plaster is hard, but still wet enough to easily carve. This is a good time to trim off the rough edges by hand or start carving your designs. It can take many months for a large plaster mold to completely dry out, so it will continue to get lighter as that happens. But it is usable immediately. If using the same piece of plaster over and over, it will eventually become too wet to release the clay. Let it dry and it will again work fine. If you can't wait for the plaster to dry, you can sprinkle it with talc. One nice thing is, if you ever want to carve into it later, you can soak it in water, re-wet it and it will become soft enough to carve into. You can do this at any time. Bags of plaster should be kept in a dry place. If you have a part of a bag left over, roll the top of bag down and secure and then put the bag inside of a plastic bag and tie shut. If they absorb a lot of water in the bag, they set up much faster and are more difficult to work with. If your plaster has absorbed water, you can refresh it by heating it to around 700˚F to remove the moisture. If you follow even half the tips here, you still should get a pretty decent mold.
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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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