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limit to multiple firings?

For discussion of processes related to using Bullseye glass, including kilnforming and kilncasting, torchwork, blowing and stained glass.

limit to multiple firings?

Postby melaniedrown » Tue Jan 12, 2010 1:01 pm

Is there a limit to how many times a piece can be full fused? We have a customer who has worked on a piece (a mask) approximately 10x16" BE double layer irid transparent with elements of frit and dicro; after each of 3 full fuse firings, she decided to add more "decorations" to it; including firing over fiber paper cut into designs (bas relief), adding additional frit, etc. The piece fired successfully until the fourth (and last) firing, where the piece was slumped over a large platter(which was lined with thin fire paper). I used a very conservative firing schedule, which I can send if necessary. (I did not exceed 200 degrees per hour on the ramp up; top temp was 1220 degrees in a skutt glass kiln with side elements. My first questions, tho, is does the glass tend to "weaken" upon multiple firings? or change its coefficiency? Do the additions of copper wire in between layers play a role in disaster upon slumping?
Thanks for any input!!
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Re: limit to multiple firings?

Postby marykaynitchie » Tue Jan 12, 2010 1:26 pm

Hi Melanie,

Thanks for posting, and providing quite a bit of information about this piece. If you have photos, or can list the style numbers of the glasses used, members may provide more specific feedback to your questions about what might have happened with this particular piece. Meanwhile, I have commented on your questions below in a general way.

melaniedrown wrote:Is there a limit to how many times a piece can be full fused?

There is not a single answer to this question. Some glass styles can be fully fused many times without any noticeable changes. Other glasses have a tendency to change under repeated or prolonged firings. This article has more details about how Bullseye glasses are tested under the "Compatibility" section.
http://www.bullseyeglass.com/pdf/produc ... Expect.pdf

melaniedrown wrote:Do the additions of copper wire in between layers play a role in disaster upon slumping?

I don't think we have fired copper wire very often in the Research and Education Department, so other readers may be able to address this question better than Bullseye's staff. However, I will give it a shot: copper wires may cause thermal shock, because copper conducts heat more readily than glass. During a firing, a section of glass directly in contact with a hot copper wire can be hotter than a different section of the same piece of glass which is at a distance from the copper wire. If the difference in temperatures in the same piece of glass is high enough, the piece can break.

Also, copper wire is not tested to be compatible with Bullseye glass, so there could be a compatibility problem as well. (Members, if you have experience firing copper wire, feel free to reply in this thread.)

Also, how large was the kiln shelf? Were the edges of the piece very close to the elements?

Mary Kay Nitchie
Bullseye Glass Co.
Mary Kay Nitchie
Bullseye Glass Co.

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Re: limit to multiple firings?

Postby melaniedrown » Wed Jan 13, 2010 11:45 am

Hi Mary Kay. Thanks so much for your quick reply. I had fired the mask on a full shelf which is quite a bit larger than the mask itself; therefore no part of it was in real close proximity to elements. I have taken a picture which I will submit. Upon closer inspection, it appears that the glass began to break at the point where the copper wire was attempting to "slump" over the mold, then just continued on its path right through the entire piece. We have used copper wire in many applications over the years, from thin wire to copper mesh and foil, mostly with great results. I appreciate your feedback and am so thrilled that Bullseye has this service available! Our studio is a big fan!
Melanie Drown
Stumptown Art Studio
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Re: limit to multiple firings?

Postby beth » Wed Jan 20, 2010 11:49 am

I just joined, hope I am ok here. In regard to using copper wire in slumping: I found that screening & wire will not always bend with the desired depth of a slump, if the slump is fairly shallow I've had no problem. I think that the wire is firmly fused into the glass & breaks the glass then when trying to bend into the slump.
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