Topic: Can cracks in kiln create thermal shock?

[Dahammar]

Hey there.
Here goes my first post. I’ve been working with glass for 20 years and have never had problems with cracks or thermal shock.
However on my last piece I keep getting thermal shock. The pieces is barely 5 mm thick and is cooled down slower than what’s bullseye recommends. I’ve tried remelting but as one crack closes a new one appears.
Using polarised glass I see the tension is only where the crack is.

So.
My kiln is ten years old and it can’t be completely closed. You can fit a piece of paper in here and there but nothing worse than that.
Could this create a draft or something that sends cold winds through the kiln?
Will try to block the gap today with some fiber but if that doesn’t work I’ve got no idea what to do.

[chopin-liszt]

Hello and welcome. 
I think the person here who would be able to discuss this in detail with you would be Adam Aaronson.
Link to his website:-
https://adamaaronson.com/

I am replying to say both welcome, and to make sure I have his name written here, so he will be able to find this when he has a look to see if he is being asked for. 

[Fuhrman Glass]

judging upon what you said about the results you got from checking on the polarization stress factor, I think you may have a compatability problem in the glass. That small crack in your kiln should not make that much difference from my experience.

[chopin-liszt]

Thank-you for your expert opinion Fuhrman Glass. I should have added your name above too, but you found the query.

[Dahammar]

thank guys.
I know.. it has to be some incompatible glass in there.. But I only use bullseye and tekta in the kiln.. could it be that clear bullseye and tekta can create this effect?
Two sculptures are ruined now so I am cleaning my workstation and starting with new sheets.. will write here about the result.

too bad we can only upload 500 kb pics ..

[chopin-liszt]

Are you using any colours you are not familar with using together?
Have any colour recipes changed? Or even your cullet recipes?

We do have a help page for resizing images and posting them directly to the board.

https://www.glassmessages.com/index.php/board,22.0.html

You just need to find the bit that tells you how to operate the systems you use.

[Dahammar]

No its a piece with just clear and light blue. and the cracks has only happened in the clear glass.

Even lost my main studio 6 months ago so I have moved everything. The only other glass I have ever fused was effetre.. but I got rid of all that in the move. And in hoping it was the annealing I have fired the piece 4 times trying to fix it..

[Fuhrman Glass]

  Look on Bullseye's website and read the pages Dan Schwoerer owner of Bullseye wrote on Compatibility and how some glass even though it is the same COE is not compatible due to differences in viscosity.

[Dahammar]

So I started over again .. new sheets of glass and it worked.. not sure how some incompatible glass landed in my bullseye, but at least I can keep working now

[chopin-liszt]

That's a big relief. 
This must have been very worrying, frustrating and expensive.
We'd love to see your work. Are you able to post any images, or perhaps provide us with a link to your website?