Slumping Glass that's
Larger than the Mold
It's common to determine the size of a fused blank by tracking
around the outside of a bowl, plate, or platter mold. This is
an easy technique, but it can lead to a situation where the
finished, fused blank is larger than the mold being used.
This does not have to be a problem. So long as the
blank is less than about 1/4" (6mm) larger than the mold -- that's
1/8" (3mm) on all sides -- it should slump easily. About the
only concession you should make to the larger than normal blank is
to make certain you slump at a fairly low temperature. For
most molds, below 1200F/650C works well. Don't worry if the
slump takes slightly longer than normal. Just keep your eye on
the slump and the slight overhang won't cause any problem.
If the overhang is greater than 1/8" (3mm) on all sides, then
it's more likely that you will have a problem with the overhang
bending down and trapping the mold inside the glass. In this
situation (and assuming an alternative mold isn't available), it's
best to go even slower and lower and watch even more carefully.
You might also consider adding a bit of fiber paper (1/8" thickness
works well) to the outside of the mold to cushion the glass and
prevent trapping the mold.
Note that this tip is primarily for slumping into
a ceramic mold. Slumping over molds or into stainless steel
molds behave differently.
Copyright 2005 Brad Walker.
All rights reserved.