Question about schedules
- This topic has 6 replies, 4 voices, and was last updated 8 years, 5 months ago by Anonymous.
- May 14, 2013 at 10:20 am #9965lorinParticipant
Good morning! I browsed the topics and could not find anyone with this question. I am brand new to firing glass. I bought a Paragon CS-16D. I followed your schedule for full fusing a two layer 6 1/2 inch plate. Before I started the kiln I reviewed the segments and it looked fine. AND the glass came out great. But your schedule said it would take approximatley 14 hours to run but it actually ran 23 hours. Before I call and ask Paragon if I am having a problem (and look like an idiot) could anyone tell me if this is normal? Thanks for any help you can offer this newbie.May 14, 2013 at 1:49 pm #12916AnonymousInactive
Did you leave the kiln closed until it got to room temperature? If so that would explain it.
Kilns cool very slowly as they get closer to the outside temperature – much slower than called for in the schedule. Most people (myself included) start venting the kiln when it gets to 500° F or so by wedging the lid open slightly with a little fiber board or similar. Just be careful not to go so fast you thermal shock your work.
May 16, 2013 at 11:05 am #12917lorinParticipant
AHA! I thought I should never ever ever open the kiln until it said “completed”. The last segment didn’t end until 23 hours. A very loooong 23 hours. Thanks for the quick response!
onward and forward.May 18, 2013 at 5:18 am #12918wordanaParticipant
Also, that’s a 16″ firebrick kiln running on 120 V. 16″ is about the maximum size that can run on a 120 V circuit. Your “as fast as possible” temp is going to be a lot slower than a smaller kiln or the same size or larger kiln running on 240. My Paragon Fusion 14 (14″) is pretty slow getting up to full fuse temps.
I still love it .
Jester’s Baubles Fused Glass DesignsMay 19, 2013 at 10:20 am #12919JeffPParticipant
I also have a Fusion 14 and have a lot of devit problems with Bullseye glass, especially opals. Do you experience the same and do you think it is the slow rise to temp?
JeffMay 19, 2013 at 11:52 am #12920wordanaParticipant
I use System 96 glass, but I rarely get devit. There are a couple of colors I’ve had problems with – dark purple transparents and a cream-colored opal. I think it’s just the tendency of the glass, not the kiln.
If you use ThinFire, try using kilnwash. I hear many anecdotal reports of ThinFIre causing devit on Bullseye. Ironic (and questionable IMO), since Bullseye makes both .
Jester’s Baubles Fused Glass DesignsMay 19, 2013 at 4:18 pm #12921AnonymousInactive
A bit of background on devit can help understand how to minimize it.
Most materials are crystalline solids – meaning that all the atoms and molecules are arranged in a pattern. Glass is an amorphous solid – meaning that there is no pattern and every molecule is more or less arranged differently. The literal meaning of word devitrification is to become un-glass-like. ie Put another way, devitrification (devit) is thecrystallization of the materials in glass.
Material can only crystallize when there is a nucleus (think “seed”). In glass, there are two potential sources for the nucleus: contaminants (“dirt”) or the clustering on glass molecules.
The key to minimizing devit is to deny it a nucleus. As glass artists, we have two ways to do this:
1) Clean our glass as well as possible. Anything on our glass that does not burn away 100% can be a nucleus for devit. Oils (from your cutter or your hands) are especially hard to clean off completely. In our studio we never use oil in our cutters (which works just fine). Also, a stiff buffing of your glass with a new, dry, white, and unprinted paper towel typically gets oils off better than using lots of glass cleaner (most of which have oils in them). Printing inks are often petroleum based which is why you should stick to unprinted paper towels.
2) Fire your glass at the lowest possible temperature to minimize fluidity of the glass. The less fluid the glass is, the less molecules can move about and cluster.
Once the process starts it will accelerate – which is why secondary firings always seem to devit more even when we clean our glass well and fire to the same or lower temperature.
My experience is that Bullseye and Spectrum both do an excellent job formulating glass that is devit-resistant – but there is only so much you can do to fight the inherent nature of the materials. Over the years, I’ve come to care less about devit (most of my work takes 4 or more trips through the kiln) and just plan on a step to fixing it at the end of the creation process.
Fixing it, btw, usually means sandblast and fire polish (or slump for a matte finish) OR thin-cap the glass with crystal clear glass powder or Super Spray. It typically adds a firing, but that’s a small price to pay for work with a pristine finish.
Helios Kiln Glass Studio
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