I have just started doing some fused glass experimenting in a
small kiln (6 x 6 x 3) --Can a small cast iron, steel or aluminum
shape be used as a mold? They would not melt at the 1500 or so
temperature of the full fused glass -- but the expansion and
contraction of the metal may cause an issue. Does anyone know? Also
---do I need to coat the metal with kiln wash?
You can get answers to questions about glass fusing and casting at
the warmglass board at www.warmglass.com. I was a moderator on that
board at one point in time but have no present affiliation.
As for your questions…Aluminum won’t hold up to the heat of
casting which requires about 1500F or higher.
Molds of any material must be coated with kiln wash or the glass will
stick. Firing glass inside of metal is problematic because of the
expansion/contraction issues. It may get stuck or it may break. I
have successfully slumped glass inside of metal molds, but they were
simple bowl molds and were only slumped, not taken to casting temps.
Typically, cast glass is fired in a refractory material, such as
jewelery casting investment or casting investments that are
specifically designed for casting glass. I have personally used
jewelry casting investment with success when casting glass. Using a
one-time mold materials like investment will allow for undercuts,
which can’t be done with a reusable mold.