shatter after slump

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  • #9677

    Hi there,


    I fused and slumped two bowls of identical glass (96) using the same mold.  One is fine, one shattered after being out of the kiln for an hour.  I was using stip construction on both and the only difference was that in the broken bowl I filled in the cracks with frit I made from the glass I used to contruct the bowls.  I probably didn’t wait until the 2nd (broken) bowl was room temp. before I removed it from the kiln.  I know the glass was compatible and that’s not the issue.  I used two different slumping programs but the top temp and the anneal time ws the same.  Do you think that removing it from the kiln before it was room temp. could have caused the break or do you think the frit in between the strip may have caused the problem?  Or, something else?  Any “best guesses” out there.  Thanks – Helanna

    Stephen Richard

    I’m guessing it was the changing of your schedule that is the most important element.  Please give the two schedules, and the thickness of the piece (or width of the strips) to help us help you.

    Stephen Richard

    blogs at: and


    Glass that breaks long after coming out of the kiln does so for one of two reasons:

    – poor annealing

    – incompatible glass

    At just an hour out of the kiln the piece could still be cooling (especially if it was hot when it came out) and thermal shock is a possibility.

    Often, the glass is actually cracked when it comes out of the kiln but we don’t notice it. Once cracked, even the “normal” stress that is in all glass may continue to increase the break until it becomes more visible.

    – Paul

    Helios Kiln Glass Studio


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