Shattered/Broken Glass

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    I started a pocket vase today.  Varigated brown textured glass, on paper on the floor of the kiln.  I peeked to check (around 1400) & noticed the bottom layer of glass had broken into several pieces.  The pieces had shifted and scattered as if the kiln had been shaken, the top piece was still intact and in place.   All glass was clean, dry, and free of debris. Any ideas as to why this might have happened and how to prevent it from happening again.




    Two problems:

    1. Never fire directly on the floor of the kiln.  The inability for the air to circulate below the work makes it exceptionally difficult to heat the glass evenly.
    2. Pocket vases are problematic because the material holding the pocket open insulates some of the glass below out.  The glass that sticks out heats quickly – the glass under the fiber paper (or whatever you use to hold the pocket open) heats slowly.  The result is thermal shock.

    We used to do pocket vases in one of our classes but stopped — they just thermal shock too easily.


    Helios Kiln Glass Studio



    We fire up lots of bud vases each spring, with good success.  I agree that you need to fire on a shelf ~ we always fire on thin fire.

    Having said that ~ the size of your vase could be the problem.  You didn’t say how large it was.

    We try to stick within a  4″ x 6″ format or smaller. 

    We also use a single layer of 1/8″ shelf paper for the pocket ~ a second piece can be put on top of this layer, but make it smaller.  Your “cover” glass will shape around it.  Make the opening smaller at the top and larger at the bottom.  That way it holds a good bit of water without spilling easily.

    We have also used “wads” of shelf paper that is thicker.  The “wads” are pieces of pre-fired 1/8″ shelf paper (fired for other purposes ~ but saved because it had not totally degraded.)  Harder to use, but nice effect.

    You also did not mention how fast you fired your kiln.  I like to speed things along, but for the vases I’ll ramp at about 500 degrees ~ and finish at approx. 1400 degrees or less.  Then cool to room temp ~ don’t peek……ok….fast peek at finish temp.

    We had some splitting of the bottom layer if we used any frit & streamer glass for that first layer.

    So we don’t use that.  Good luck.  I have one small orange bud vase on my kids site:  Check it out.

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