General Question

Mariah's avatar

What, besides coefficient of expansion, could make two pieces of glass incompatible for firing together?

Asked by Mariah (25876points) December 25th, 2011

No idea if anyone here will have this info for me, but I figured I’d try.

When firing glass in a kiln, it is important to use consistent coefficients of expansion within a piece. If one layer expands more quickly than another, the piece will break.

Are there any other factors that could make glass incompatible? Melting point, maybe?

Before today I only had Fuseworks brand glass, but today I got a lot of wonderful glass of the same COE, but a different brand. Now I keep reading that Fuseworks glass isn’t compatible with other glass, even of the same COE, and I can’t understand why. I’m wondering if this is just their marketing strategy to discourage you from buying from other vendors.

Maybe I’ll just have to try it and find out, but does anyone have a clue?

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9 Answers

Tropical_Willie's avatar

Melting point would be my guess. The Fuseworks is for microwave kiln use.

Mariah's avatar

What I have is a microwave kiln….shoot, I’m hoping this doesn’t mean that the temperatures in my kiln won’t get high enough to melt my new glass!

If I can get the new glass to melt, do you have any idea if it would be a problem for different layers in the same piece to be melting at different times? Could this cause breakage or other problems?

Tropical_Willie's avatar

The melting point I believe is GREATLY different. Like hundreds of degrees. I don’t know, what is the maximum temperature for microwave kiln?

Mariah's avatar

Apparently it can get up to 1600. Fusing stage for regular (non-Fuseworks) glass is about 1450–1550 so it should be useable. I suppose though that if I used them together the fuseworks glass might be a puddle before the other glass even softens. Gah. Thanks for your help!

Mariah's avatar

Update: I fused two pieces today; not only can my kiln melt the off-brand glass easily, but mixing Fuseworks and off-brand glass was no problem either. Two successful firings. Yay!

Tropical_Willie's avatar

That’s good.

How are you able to anneal the glass after fusing?

Mariah's avatar

@Tropical_Willie Doesn’t annealing happen naturally as the glass cools? I don’t know, I’m such a newbie at this!

Tropical_Willie's avatar

Annealing is the slow slow drop in temperature. Glass after it is heated needs annealing look here. This is a good place to go to understand glass art.

Mariah's avatar

@Tropical_Willie There certainly isn’t a large amount of user control over the way glass cools with a microwave kiln, unfortunately. The glass is to be left inside the kiln for at least half an hour (I usually wait longer) after removal from the microwave to prevent thermal shock. Because the kiln is a very good insulator, it does cool quite slowly inside the kiln. It’s possible it doesn’t cool slowly enough, though; it’s hard to tell because there’s no way to measure the temperature inside the kiln. I have never had a piece break after firing, though.

Thanks for the links; I have a lot to learn! If I get serious about this hobby (and I think I will because I am really enjoying myself) I will eventually invest in a tabletop kiln. That’ll have to wait until I am done with college though.

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