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Plaster/Silica Mixtures for Mold Making
The traditional mold material used for kiln
casting is a 50/50 mixture of plaster and ground silica. This
produces a mold that is inexpensive and will work fairly well for
small projects. For larger items it's often better to
reinforce the plaster/silica or even use an investment other than
plaster/silica.
Normally, the plaster used can be any of the
commonly available pottery plasters. Even plasters such as
Plaster of Paris will work well for most purposes.
Silica, which is a hazardous material that
can cause silicosis (a lung disease), is generally used in powder
form. 200 mesh works well. In some places ground silica
is also known as flint or silica flint.
Although the traditional mixture uses equal
parts of each of these two ingredients, the ingredients do not
generally need to be measured precisely (especially when used in
small molds). It's acceptable to add more silica than plaster
-- adding up to two times as much silica will leave a softer mold
that can easily be carved and shaped after it sets.
Click
here to go to part two of this tip, which deals with mixing plaster
and silica together.
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Copyright 2005 Brad Walker.
All rights reserved.
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