Not compatible glass after all

BobB · Post by **BobB** » Fri Jun 20, 2003 2:00 pm

Just as an FYI!

I took some of our stained glass stock (spectrum unknown COE) and ran some fusing tests. I found several colours that fused ok with a clear. So I thought great the glass is compatible. I made a couple of projects with the glass and everything seemed to work fine, no cracks, no problems. HOWEVER; cut one piece up into smaller piece to foil into a stained glass panel to give it more colour. Heating these pieces with a soldering iron caused small (and getting bigger) cracks all through the fused pieces of the panel. Apparently the glass wasn't as compatible as I thought.

BobB

Tony Smith · Post by **Tony Smith** » Fri Jun 20, 2003 10:56 pm

When you say they "fused ok with clear" did you check them under a polarizer for stress? What made you think they fused okay?

Tony

BobB · Post by **BobB** » Sat Jun 21, 2003 10:07 am

No Tony I didn't use a polarizer. I've been checking the pieces on a light table and looking at them with a large magnifying glass. I let them set for a few days in the shop and check them again. Generally I can spot cracks at the edges of the glass even if they are small. Obviously this technique is not thorough enough. It makes me wonder if I apply a little heat to the others will they crack too.

BobB

Tony Smith · Post by **Tony Smith** » Sat Jun 21, 2003 12:03 pm

The only way to tell if you have stress in the glass is to look at the edges (through the clear glass) with cross-polarized light. Otherwise, you have no way of knowing if you have a piece that will break five minutes from now, or five months from now... stress in the glass is like that.

You can use polarized sunglasses to do this... just pop out the lenses, rotate one of the lenses with respect to the other over the light table until you get maximum cancellation (no light through) then put your glass in between the lenses. Bright areas will indicate stress between the fused pieces.

Tony