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| Author | Post |
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bbates
Non AGG Members
| Joined: | Fri Sep 28th, 2007 |
| Location: | |
| Posts: | 46 |
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Tue Jan 29th, 2008 07:29 pm |
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I'm painting a medallion and using a kiln that I have never used before.
I have a 10 inch opaque white spectrum glass circle (1/8" thick), I painted a design on it and fired it in a evenheat kiln. I set it to ramp as fast as possible (per the suggestion of a hot glass worker) and came to find it heat fractured.
I tried again and this time set the ramp rate at 2500 per hour. After about 15 minutes, my coworker check it, it was at 700 and the peice had already shattered. She thinks that it is a problem with the glass that I used (poorly annealled or something). So I am tryin again, this time with system 96 (fusing) glass. Same color, density, size, thickness, and brand.
Before I shatter another peice, am I missing something?
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Vic
Director
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Posted: Tue Jan 29th, 2008 11:22 pm |
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| You should go slower till 500 or so. The thin piece of glass will get hot before the rest of the kiln,shelve etc. Going slower gives everything a chance to stabilize.
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Rebecca
Administrator
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Wed Jan 30th, 2008 01:07 am |
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Vic's right about increasing the temperature more slowly. I just wanted to add that I have had a lot of divitrification with regular white Spectrum. I would use the System 96.
Rebecca
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Ardbeg
AGG member
| Joined: | Tue Oct 24th, 2006 |
| Location: | United Kingdom |
| Posts: | 67 |
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Posted: Wed Jan 30th, 2008 09:44 am |
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Also, let the glass "rest" about 3/4 of the way up to top temerature, this allows it to anneal properly, and reduces the risk of internal fractures and stresses. Same for cooling down
You should have manufacture guides / glass specs for this annealing temperature, each glass is slightly different.
Linda
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Steve
AGG member
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Wed Jan 30th, 2008 02:05 pm |
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I use Evenheat kilns exclusively, GTS-23-9, with rampmaster controller, and I also paint alot of pieces nearly the size of the 20" kiln shelf. My best and most consistent results are when I set the controller to ramp at 300 deg/hr to a temp of 750 ( then I know I am thru the fragile range of whatever glass)then ramp at 1250/ hr( or whatever speed you want really) to completion. Since using this schedule, with several different manufacturers glass, I have not lost one, and the Devit problem with Spectrum is greatly reduced if not eliminated. Admitedly, I use very little Spectrum though.
I should also add that for painting I do not use a mullite shelf, I have some old fireproof ceiling tiles that I have cut and use for paint.
Last edited on Wed Jan 30th, 2008 02:07 pm by Steve
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