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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.

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Copyright 2005 Brad Walker.  All rights reserved.

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Copyright 2005-2006 by M. Bradley Walker.  All rights reserved.

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