Warm Glass
FILLING THE MOLD WITH GLASS
Once you have removed the the model from your mold and cured the mold so that it is ready for firing, you are ready for the next step in the kiln casting process, filling the mold with glass.
The first major consideration is to determine which size of glass to use. As was noted before, size can range from very small particles to large chunks. In general, the larger the chunks of glass the clearer will be the final casting.
In addition to size, you should also determine the type and color of glass to use. The type of glass is significant for two main reasons: first, you must use compatible glass; second, you should use a glass that is not prone to devitrification. The longer soak times typically used in kiln casting make controlling devitrification even more important than in fusing and slumping.
Color of glass is primarily an artistic choice. However, if you desire a clear casting, there are a few basic principles to keep in mind. Use larger chunks of glass, rather than smaller. Help prevent devitrification by using glass that has been specifically formulated for casting. Note also that many "clear" glasses actually have a greenish tint; if this is not desirable, seek out a special "casting clear" (sometimes called "Colorless Clear") that has been formulated without the green tint.
Once you've determined the color, type, and size of the glass to be used, you'll need to decide the method you will use to fill the mold with glass. There are three major alternatives, each of which results in a different final appearance.
Probably the easiest approach to filling the casting, this method usually results in a relatively homogenous casting that can vary from transparent to opaque depending on the glass used.
Best for situations where you want the casting to be as clear as possible, this method requires a kiln with a relatively high clearance. It also requires a "crucible," a container to hold glass frit or chunks that can resist the heat of the kiln.
Probably the most technically challenging of the three methods, this is best when you want to precisely control the particular colors and density of the glass used.