Question:
How do I make a simple mold?
Making a mold with a master
Another way to use plaster is to pour it into and around existing objects. 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. For example, say you carved a relief design into a slab of clay, and you want a mold of it so you can make exact duplicates of that design. First you need to surround your slab with something to hold the plaster.
Pottery Plaster
Buy plaster. When casting molds, 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.
Put on a dust mask when handling dry mixtures of this type.
Trimming and carving
There will be a point where the plaster is hard, but still wet enough to easily carve. This is a good time to put the item on your wheel and trim it, or trim off the rough edges by hand, or start carving your designs.
Slab flop mould
Slab flop mould:
Anything can be used as a mould, although plaster is preferred, any object can be used.
Roll slab as in introduction, leave it to firm approx 1/2 hour.
Gently insert slab into mould and press against walls, trim excess, and leave till leather hard. Remove from mould and allow to dry. The piece is now ready for bisquing!
Total de-airing
Use rubbing or denatured alcohol in a spray bottle (some people dilute, some don't). 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 especially useful if you will be using the top surface of the mold you are pouring.)
Pouring Airless plaster
The goal in pouring the plaster is to avoid introducing air pockets, particularly at 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, thus slowing it down.
Slab hump mould
Slab hump mould:
This is a similar technique to the slump moulds, except that we are using the clay over the mould instead of in the mould. Roll slab as in introduction, place it straight over the desired mould with a piece of newspaper between. The difference between the two techniques starts here, because clay shrinks, the form must be watched closely, and removed before it shrinks so much it cracks. When dry enough to handle, gently remove from mould and place rim down to dry. The piece is now ready for bisquing!
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| Guru Spotlight |
| Patricia Walters-Fischer |
