Disaster! Is this a kiln problem? - WarmGlass.com

Disaster! Is this a kiln problem?

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Mark Wright
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Joined: Mon Dec 13, 2010 12:43 pm
Location: Raleigh, NC

Disaster! Is this a kiln problem?

Postby Mark Wright » Wed Jun 01, 2016 4:12 pm

I hope someone has seen this before and can tell me where to look for the problem.

Two bubble-up firings. The first is fine and was slumped into a plate. Next was 4 smaller pieces on the same schedule. All have multiple cracks. The cracked one in the lower right is even the same glass. What happened?
Everything was the same except the size of the glass (7” vs 4 ½”) a different kiln shelf and I noticed the total time in the kiln was 8:02 vs 8:20 for the ones that cracked. Cracks are sharp so it happened on the way down, and some places are really stuck to the kiln shelf. Thermocouple bad? Controller bad?
Schedule:
400/hr to 1100 hold 10 min
AFAP to 1700 hold 45 min
AFAP to 925 hold 60 min
100/hr to 750 off

No problem here
1st plate.jpg


Disaster
4 in kiln cracked.jpg


Spread out
4 spread out.jpg

Brad Walker
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Re: Disaster! Is this a kiln problem?

Postby Brad Walker » Wed Jun 01, 2016 4:24 pm

Probably not enough kiln wash. Most likely, sticking in some places.

Tony Smith
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Re: Disaster! Is this a kiln problem?

Postby Tony Smith » Thu Jun 02, 2016 6:20 am

I'm with Brad. Especially with a new kiln shelf, if the kiln wash is too thin (or nonexistent), the glass sticks and tears itself apart as the kiln cools. Are there bits of kiln shelf stuck to the bottom of the glass?

Tony
The tightrope between being strange and being creative is too narrow to walk without occasionally landing on both sides..." Scott Berkun

Mark Wright
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Joined: Mon Dec 13, 2010 12:43 pm
Location: Raleigh, NC

Re: Disaster! Is this a kiln problem?

Postby Mark Wright » Thu Jun 02, 2016 8:35 am

More kiln wash seems like an easy fix. My notes say I used 8 coats on both firings, but I have been known to be senile. I will try again and see what happens.

Valerie Adams
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Re: Disaster! Is this a kiln problem?

Postby Valerie Adams » Fri Jun 03, 2016 5:43 pm

Why are you firing to 1700°?

Tony Smith
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Re: Disaster! Is this a kiln problem?

Postby Tony Smith » Sat Jun 04, 2016 7:23 am

Good point.

Why are you firing so hot? You're in the domain of combing temperatures... well beyond where kiln wash breaks down.

Tony
The tightrope between being strange and being creative is too narrow to walk without occasionally landing on both sides..." Scott Berkun

Brad Walker
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Re: Disaster! Is this a kiln problem?

Postby Brad Walker » Sat Jun 04, 2016 7:56 am

This is a high temperature firing. Like combing, you need to fire hot to get the particular effect you're after.

Mark Wright
Posts: 49
Joined: Mon Dec 13, 2010 12:43 pm
Location: Raleigh, NC

Re: Disaster! Is this a kiln problem?

Postby Mark Wright » Sat Jun 04, 2016 11:59 am

The experts were right. Not enough kiln wash. My notes say 8 coats of kiln wash, but my guess is I was distracted with something and picked up the wrong shelf. Thanks for the help. This BB may be one of the best "tools" I have.
As Brad mentioned it takes 1700 to do a Bubble Up. Brad originated this at Warmglass and teaches classes for it. A great class and I highly recommend it. Lots of fun.
Mark

The latest with 8+ coats of kiln wash. No cracks!
Bubble Up retry.jpg


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