Saturday, August 24, 2013

Fused Glass Learning Experience: Thermal Shock?

Remember back when the only decision was which side should be the inside of the bowl? 
Just a matter of days ago, we were debating which side would be best for slumping into the inside of the bowl.

Scott did a bit of coldworking on it with loose silicon carbide grits to make it smoother and remove any devitrification, and then it was time to put it back in for a fire polish.

No big deal, right?

Heartbreaking, isn't it?
The piece shattered with enough force that it pushed the smaller piece off the ThinFire paper the piece sat on.

Unlike the last time this happened, this piece broke while the kiln was heating up. The edges where it broke are smoothly rounded over, so it doesn't even fit together cleanly anymore. (The purple and green piece you can see in that link broke after it came out of the kiln, so the edges were sharp and it was fairly easy to push together and fuse

Close, but no cigar.

The good folks at the Bullseye Glass resource center say it's likely that although the kiln fired on a fairly conservative tack fuse schedule (the initial heating was 300 degrees per hour to 1200 degrees), the thick glass (about 9mm, or three layers of glass thick) really needed an even slower heating schedule, somewhere between 100 degrees and 200 degrees. Sigh.

Although I wish it hadn't broken, it's kind of neat to be able to see the layers of colors in the glass.
The Bullseye techs offered several suggestions, ranging from intentionally highlighting the break (which is apparently a popular style in Japan) to fusing it with a solid circle of thin clear glass enough to let it flow a little, and see if it comes together in a way we like. Scott is leaning toward the latter, and we'll see how it comes out.

But the glass has already been through the kiln five times in its various stages, which is the limit of what Bullseye tests its glass to be able to do, so it's possible that the glass won't really be salvageable. That's what learning experiences are all about, right?

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