The raditional glass casting formula is 50% plaster and 50% silica flour.
Depending on the shape of the mold and the temperature taken to it is
possible to get more than one use from this kind of mold.
If you are trying to make the shape of the back as well as the overall
shape, life is a lot trickier.
In annealing the glass, you have to take into account the thickness of the
mold.

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Mike Firth
Hot Glass Bits Furnace Working Website
http://users.ticnet.com/mikefirth/hotbit47.htm Latest notes

"A.Rahim Sheikh" wrote in message
...
hi,
I want to make a particular glass lens for a car, i need to make a mold
from a refractory plaster/ ceramic, then slump the glass into the mold .
please help. does anyone have a formula for cerating glass slumping molds?
thanx