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Working Deep--help with trapped bubble

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Working Deep--help with trapped bubble

Postby celeichter » Sat Aug 04, 2018 2:00 pm

Hi, everyone! And thanks in advance for any advice you can give!

1) I work in deep glass, multiple layer images in powder frit. Each layer is fired separately, then all put together in a damn mold and fired to form one block. I put clear powder between each layer when firing them all at once.

2) 2 photos are attached, one showing the collapsed bubble and one showing the attempted repair

3) All powder frit, some transparent and some opaque but mostly opaque, COE 90.

4) 10" x 10", six layers of tekta with image elements made of frit; some (very little) use of glassline enamel.

Kiln and firing info:

1) Olympic 146 slider with RTC-1000 controller; 14.5 x 14.5 x 6 firing chamber - plenty of room for what I'm doing.

2) For the combined piece: 300 to 1225, 1 hour hold; 600 to 1490, 15 min hold; Full to 900, 4 hour hold; 27 to 800, one minute hold; 49 to 700, 1 minute hold; 162 to 70, i minute hold

Kiln Furniture and supplies

1) The kiln shelf is one I ordered with the kiln, an Olympic 146 slider with RTC-1000 controller

2) I'm using thin paper as the separator

3) The piece is square in the middle of the kiln

4) I'm using a dam mold, 10" square and about 3/4" deep, lined with thin paper on the bottom and sides and fiber paper also around the sides

Here is what happened:
The individual layers fired just fine. When I fired the whole thing, in its dam mold, it came out with a huge collapsed bubble in the middle that went down to the bottom layer. The leopard's face looked like it had semi-melted downward, with a big black blot where its nose should be.

(I should note that I had previously fired multi-layer pieces in the kiln with no trouble.)

My glass teacher suggested I just rebuild the face and refire. That has worked to some extent, but there seem to be furrows down the slopes of the muzzle where the glass doesn't seem to stick, or it melts into the "walls" of the bubble - in any case, there are what amount to "blank" areas that resist efforts to fill them in.

Do you have a hunch about what could be done differently to avoid the problem? - No; I don't know what caused the original problem nor why it can't be fixed. Everything is fairly new; the kiln is level, and I used clear powder between my layers.

Thanks for reading this. We look forward to helping you.

And advice you can give would be much appreciated!
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Re: Working Deep--help with trapped bubble

Postby marykaynitchie » Wed Aug 08, 2018 9:07 am

Can you try to post the photos that you mentioned?

Mary Kay
Mary Kay Nitchie
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Re: Working Deep--help with trapped bubble

Postby jestersbaubles » Tue Aug 14, 2018 7:19 pm

You have no bubble squeeze in your schedule. A bubble squeeze is not just "a long hold at 1225". A bubble squeeze consists of a very slow ramp from approx. 1000/1100 to 1225/1250 (slow, as in 50 deg/hr), then the long hold.

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