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Hello,

I've been getting devitrification on the bottom of my glass (not the top) when firing a full fuse in my new Profusion 16 fiber kiln. I was not told that it needed prefiring when I purchased it. (I hope I am saying this correctly.) I only read this on some of the topics here. I read that it should be prefired about 100-200 degrees hotter. Hotter than my normal full fuse program? And does it run through the entire (each segment) full fuse program at 100-200 degrees higher? I appreciate any help. I am very new to this and trying to learn all the new terminology.

Thanks Deborah

Just fire it at 9999 up to top temp and hold for 15 OR so min. Leave out a peephole plug or vent in some other fashion throughout. The firing.

Devit on the bottom is strange. What kind of shelf and kiln wash and glass are you using? Make sure the shelf is in the kiln when you do what Rosanna suggested.

Warren

you're picking up the pattern of whatever you're firing on, and tiny particles of that (if you're using wash, fiber, or some sort of paper). it's not devit. you can't get the bottom of a fused item to be as shiny as the top.

I am using thin shelf paper I purchased on a huge roll from Delphi a few years ago (I don't think it was any particular brand name) - does not do this in my brick kiln. I used it on the bottom of the kiln itself, I also used a fiber board with hardener on it and on a ceramic kiln shelf I got with my brick kiln. I've also raised the shelf to 3 inches. I've tried everything to get the stuff off the bottom but it won't budge. I've used clear glass on some firings and it leaves a whitish tint. Almost like its been sand blasted. If it is the shelf paper what would you suggest I use to remove it? It also has a very rough surface. Would you suggest I use a different shelf paper? The one thing I have learned is that the bubble squeeze program I am using works. lol

Thank you all for your input.

Deborah

Try a firing with kilnwash and no paper. After the initial firing of fiber boards, there are no more issues. The organic binders are gone. I suggest firing 50ºF hotter than you ever use your kiln. I only work in fiber kilns. They are far superior to brick kilns in every way. With a brick kiln, you pay more to heat it up and wait longer for it to cool down. Firing schedules could need to be different. You create your firing schedule to do 2 things. First is heatwork, followed by annealing, then followed by cooling to room temp.

[quote="Deborah Harbison"]I am using thin shelf paper I purchased on a huge roll from Delphi a few years ago (I don't think it was any particular brand name) - does not do this in my brick kiln. I used it on the bottom of the kiln itself, I also used a fiber board with hardener on it and on a ceramic kiln shelf I got with my brick kiln. I've also raised the shelf to 3 inches. I've tried everything to get the stuff off the bottom but it won't budge. I've used clear glass on some firings and it leaves a whitish tint. Almost like its been sand blasted. If it is the shelf paper what would you suggest I use to remove it? It also has a very rough surface. Would you suggest I use a different shelf paper? The one thing I have learned is that the bubble squeeze program I am using works. lol

Thank you all for your input.

Deborah[/quote]

it is particles from the fiber that are embedded into the glass. you can fire at a lower temp, and you'll get less. the only way to remove it is to abrade it away (flat lap, sand blasting, etc). i use kiln wash, and by not going over 1450 or so, i don't get much embedded particles in the bottom surface.

I can remove particles stuck on float glass, without adding scratches, with a used 400 grit diamond hand pad. With the softer fusing glasses, you might try a 600 grit pad.

In my kilns I need less heat to get the same results in my fiber kiln than in my bricj kiln. Adjust your schedules.

I don't think I mentioned the program I was using - fiber kiln - this seems to work for my bubble squeeze (few tiny champagne bubbles) but this creates the bottom problem mentioned earlier.

300F/1000F/no hold
100/1350F/no hold
300/1425F/hold 10
Full/950/hold 30

Thank you for the input you all have passed on.

Deborah,
Suggest you hold at 900 for an hour (for 2 layers)
Then 100/hr to 750, then off
This will give you better annealing.
Surprised you are getting fiber sticking on the back only going to 1425.
Warren

Thank you Warren. I may have discovered some of the problems. I will let you know when I am sure.

Thanks again for all of your input.

Deborah