Old-fashioned pottery clay is basically just a mixture of silica mineral
particles that melt into glass, or vitrify, at different temperatures. The material used for the ceramic investment in bronze casting is quite
The silica is formulated so that it will vitrify at a higher temperature than the melted bronze so that it doesn't melt when the bronze is
It also must not contract or shatter during the initial firing process when the wax is "lost," and then when the bronze is
Finally, the ceramic must be brittle enough to be relatively easy to break off once the bronze is cast.