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I had a dish crack in the slump (not break). I've used the same firing schedule in the past with no problem (though I usually do +5 deg more). I've been through my log and can't see what's different to explain it. This was a custom order dish and I really want to get it right this time, hopefully sooner rather than later!

Details:

Bullseye 2 layers, clear transparent on top.
Dish is 5 in.
Crack is curved, doesn't quite go through. One end of the curve goes to the edge of the glass, but not the other.

Firing schedules:

Full fuse:
400. 1100. 25m
400. 1350. 15m
FULL 960. 60m
150. 700. 0

Tack (dots)
400. 1300. 5m
Full. 960. 60m
150. 700. 0

Slump
300. 1245. 15m. (I usually do 1250, but have used both in the past)
Full. 960. 60m
100. 700. 0

Advice?


(After full fuse, the surface was a little bumpy --like some of the bubbles didn't quite make their way out, but if that was a problem, would the dish have made it as far as the slump?)

First-- 1350 will not give you a "full fuse" Second-- I would pay more attention to the "anneal zone" slow down eg: 80dph from 1100 thru to anneal at 950 (45 min.) then 80dph to 800. then ramp down conservatively to 100. AFAP from fuse to anneal is not a good schedule. I don't think your piece was fully fused or properly annealed!

would agree with Don and add that whenever you have tacked on elements you slow down more as there is more variance in thickness. The crack may have started at a dot.