Tuesday, 30 November 2010

Glass Compatibility

Which glass can you use for fusing glass work?

Well nearly any so long as they are compatible.

Compatible? I thought all glass was the same?

No glass types vary immensely, let me tell you all about it.

When glass is heated and cooled it expands and contracts at different rates depending on the type of glass.
To be able to tell them apart glass is given a COE number. COE stands for Coefficient of Expansion.
Window glass has a COE of 84
Pyrex glass is COE 32
Effetre glass used for lampworking is COE 104
The glass I use is bullseye glass which has a COE of 90. This is the most commonly used glass in the UK I think.
Right... so as long as you use the same type you should be fine. If the glass is not compatible it could cause cracking or even shattering of the piece when it cools.

To demonstrate the stress glass is under when fused with incompatible glass see the pic's below.

This one looks okay and seems to be fused together.

In this pic you can see the stress in the halo of light around the glass the dark gap is the compatible glass.

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