Crack on slump... Help? -

Crack on slump... Help?

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Kinsey K
Posts: 2
Joined: Wed Oct 14, 2020 1:58 pm

Crack on slump... Help?

Postby Kinsey K » Tue May 25, 2021 6:09 pm

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!


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

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


(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?)
jade dish detail.jpg

Posts: 374
Joined: Sun Mar 09, 2003 9:09 pm
Location: Ontario

Re: Crack on slump... Help?

Postby DonMcClennen » Tue May 25, 2021 8:11 pm

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!
"The Glassman"

Posts: 81
Joined: Sun May 01, 2005 9:34 pm
Location: San Diego

Re: Crack on slump... Help?

Postby Dick » Fri Jun 11, 2021 6:03 pm

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.

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