Unusual plate crack
Posted: Wed Jul 06, 2016 4:31 pm
I’ve fused and slumped 5 plates. The first cracked due to an annealing schedule that was too fast. The next two survived. The last two have both cracked in a perplexing (to me) spiral. I haven't been able to find a picture or description of anything like them in the books I have or online.
The cracks occurred out of the kiln, within 24 hours of the slump. One cracked when the plate was picked up after a piece of hot pizza was put on it. The other may have cracked in the dishwasher. (I assumed fused glass plates were DW safe because 1) DW temps are so much lower than the fusing temps, 2) ceramic glazes are glass and are DW safe and 3) the two surviving plates are also surviving the DW. Please correct me if I'm wrong.)
Slumping schedule (in F)
250/250/15
250/1050/30
50/1225/10
400/950/60
200/800/10
(The T plate is actually my 13yo son’s work.)
Slumping schedule (in F)
250/250/15
250/1050/30
150/1225/10
400/950/60
200/800/10
The two surviving plates were slumped using the same schedule as the T plate (only one is shown - the other had a white base layer and transparent blue & green with opaque white over that):
I have an Evenheat Studio Pro 17 and used Wissmach COE 96 3mm glass for these projects. All have clear glass bottom layers. All of the designs are in the second layer, except the T and the squares which were in a third (and fourth) layer.
I’m looking for insight into what causes this sort of crack, and what sort of schedule might prevent it. The best I can come up with is something about the light and dark colors, and opaque vs transparent, viscosities and so on. However, the shape of the cracks doesn't seem consistent with that theory.
I’m also curious about the small bubbles in all of these plates (seen as bright spots in the pictures). They were in the original glass sheets and I can’t get them out even with slow rises (50F/hr from 1050 to 1250F) and long soaks at 1250F. Is this a glass quality issue? A firing issue? Some combination? Something else?
Thank you for any help you may offer.
The cracks occurred out of the kiln, within 24 hours of the slump. One cracked when the plate was picked up after a piece of hot pizza was put on it. The other may have cracked in the dishwasher. (I assumed fused glass plates were DW safe because 1) DW temps are so much lower than the fusing temps, 2) ceramic glazes are glass and are DW safe and 3) the two surviving plates are also surviving the DW. Please correct me if I'm wrong.)
Slumping schedule (in F)
250/250/15
250/1050/30
50/1225/10
400/950/60
200/800/10
(The T plate is actually my 13yo son’s work.)
Slumping schedule (in F)
250/250/15
250/1050/30
150/1225/10
400/950/60
200/800/10
The two surviving plates were slumped using the same schedule as the T plate (only one is shown - the other had a white base layer and transparent blue & green with opaque white over that):
I have an Evenheat Studio Pro 17 and used Wissmach COE 96 3mm glass for these projects. All have clear glass bottom layers. All of the designs are in the second layer, except the T and the squares which were in a third (and fourth) layer.
I’m looking for insight into what causes this sort of crack, and what sort of schedule might prevent it. The best I can come up with is something about the light and dark colors, and opaque vs transparent, viscosities and so on. However, the shape of the cracks doesn't seem consistent with that theory.
I’m also curious about the small bubbles in all of these plates (seen as bright spots in the pictures). They were in the original glass sheets and I can’t get them out even with slow rises (50F/hr from 1050 to 1250F) and long soaks at 1250F. Is this a glass quality issue? A firing issue? Some combination? Something else?
Thank you for any help you may offer.