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I fired a painting project in my kiln made of float glass and a lot of air was trapped between the two layers. The bottom layer was painted. I am not talking about tiny air bubbles but pockets of air that made the surface look and feel like cellulite. What did I do wrong?

Secondly if I now slump this into a mould will the glass with the bubbles break or not?
Thirdly how can I avoid the problem in future?

Another problem I had was that firstly some of the paint cracked while others remained solid (paint was mixed with medium).

Secondly, the red color also discoloured to nearly a black while unsanwiched test pieces remained bright red. Why is this?by Tessa de Wet

Milly’s reply:

Lots of good questions! You don’t say how big your piece of glass was, but as you’re slumping it, I’ll assume it’s bowl-size… You get bubbles where air gets trapped between two layers. If one of the layers is painted, that will make it easier for air to trap. Did your kiln firing schedule include a bubble squeeze? For float glass, this is about 690C, from 10-30mins depending on size of glass work.

The bubbles won’t make this crack on refiring, but I would take it up slower, and make your annealing cycle slightly more conservative (ie, slow down, hold longer)

The paint cracks when it’s applied too thickly, regardless of medium. So you probably had some areas where the paint was too thick.

Red is fiendishly tricky. Did you fire the paint at a lower temperature first, and then a higher temperature for the fusing? If so, that’s why it went black. Try taking the glass up slower and test it at the highest temperature before you attempt to fuse. The sandwiching itself can also cause red to behave differently – no space for oxides to burn off etc.

I think I’ve covered all your questions – sometimes you have to do lots of different tests before you achieve what you’re after.

Good luck with your future painting and fusing projects.

 

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