Surface Bubbles on Thick Peices

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    I just retrieved two pieces from the kiln and I have an issue I would like some advice on…


    The finished pieces are one inch thick. I pre-fired four bottom layers (two separate firings of two layers each) and placed three unfired clear layers on top. Two of those layers included some Glassline paint and the top layer perfectly clear. There is a clear irid layer on the bottom (irid out). I also used clear irid on the sides and created a bullnose edge.


    There were about two moderately-sized bubbles in each piece. They are large enough to bother me, and I would like to fill them in with frit and re-fire. My question is: Should I stick to the same firing schedule for the one-inch thickness or can I shorten up both heating and cooling since I only want to heat the top enough to melt the frit into the craters?


    Here is the schedule I used for the one-inch thickness (96 COE):

    RateTemp (F) –  Hold (h.m)


    1751470 – 0.10

    AFAP – 9304.00

    25 – 775 – 0.10

    45 – 600 – 0.10

    150 – 200 – 0.00




    Your ramp up to 1250 may be too fast, but others with more experience would know better than me.

    You would still want to stick with your existing anneal and cooldown segments, IMO.

    Dana W.

    Jester’s Baubles Fused Glass Designs


    I would also go more conservative on the ramp up…especially since it sounds like a lot of work has gone into it.  Was this your original firing schedule with the layers?

    Also, instead of using coarse or other frit, small chunks of glass that you make yourself may produce clearer results, if you can fit them in there.  Maybe even small bits of clear stringer.  Coarse frit, even when washed to remove the dust, can produce tiny bubbles.

    Another thing I do…if I have bubbles that are bothering me, is to turn the piece upside down, and fire a little hotter to force the bubbles to the middle of the piece and make them part of the design!

    Laughing Kat Kramer

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