WarmGlass.com

Good morning. I bought polarizing film from Bullseye.. and held it at right angles to see annealing results on 2' x 3' fused glass. All I see is dark and clear..not hazy, not colored .. I imagine this is good news, but I would appreciate hearing from those that use polarizing film, to see if this means the glass survived its fusing journey in tact. (It is over a week out of the kiln.)

Thank you.

On a piece that has no stress, I would expect to see only dark. If there are clear spots originating from an edge or around a piece fused into the glass, that would indicate stress of some degree. Coloured indicates extreme stress.

Now I know what to look for, and I do see a slight 'haze' over some areas..I understand that is stress. Not sure how much I need to worry about it.. (?)

Awhile back, Lani McGregor of Bullseye fame wrote a nice blogpost on how they run stress tests with a polarizer. Take a look:
http://www.bullseyeglass.com/blog/2007/ ... f-the-fun/

Lani's info was excellent- thanks.. and very valuable to me was "Chips that exceed this extreme level of stress will actually break out of the bar – at which point the stress is relieved by cracking and no halo will be visible. " I am not seeing much halo now in my glass that had cracked earlier, which she explains.

But my new piece does have halos..see attached. These may be minor..but are there such things as 'minor' annealing issues, or are any bad news?

Yes there is some stress between the blue and grey in the second photo. To determine whether this is annealing or compatibility stress, you need to run a test.
The following is a method that should give you answers.
http://glasstips.blogspot.co.uk/2009/08 ... tests.html

I called the manuf. and they said it they are all compatible. ( But I am not sure I trust that.) FYI - the glass is clear..it looks grey due to color of film. I have used these colors together many, many times without issues. but lately have had less luck. I think it is annealing issues.

I would like to know if it is SOME stress, can the glass survive with that?

yes, some stress in some shapes and items can stay intact for many years. Look at some 19th century paperweights under a stressometer and you'll be amazed that they have hung together for going on 200 years. Some cracked in a few hours, it all depends on many issues.

Compatibility comes in a range. At the bottom of the range there is no stress. At the top, there is quite a bit of stress. At any point, if you add enough additional stress, you can make a crack happen.

Stresses move in different directions, like compression and tension. When you add compression the glass actually gets stronger. Glass is stronger than steel in compression. However it is weak in tension. Sometimes stresses can balance each other out, resulting in a compatible equilibrium.

After glass cracks, the stresses realign. This can change the shape of the glass. I have seen 2 pieces of glass that used to be one, line up, and they no longer aligned at the crack. One was warped in a different direction.