Help - troubleshoot cracked glass

[kdd]

I built three panels approximately 19 inches by 24 inches and approximately .25" to 3/8ths inch thick. The firing schedule I used is:
150 500 20
150 800 20
150 1100 20
50 1250 10
9999 1470 20
9999 960 4 hours
100 700 1 hour
I cold worked the panels. the client installed the panels into a window in MN.... As you'll be able to see in the pictures I have cracks in two out of three of the panels... I thought my anneal was long enough... are there other things to consider - hot - cold - stress from installing this way? Do you think the anneal is the culprit? Thank you so much for your thoughts!

[kdd]

Brad, not sure how to "Just ask Brad" but, I'd be very interested on your thoughts.

[Warren Weiss]

Hi kdd,

Beautiful panels. Your schedule is very conservative and should be fine. At most, you may want to drop your anneal drop temp. to 80 or 90f/hr. I would examine the mounting frame with a steel straight edge to look for a high spot near the middle. If there is, and the glass is pressed tight on the sides, it is inviting a stress fracture most likely to show up with a variation in temperature. I couldn't see the fracture in the top piece, but the bottom one looks like what one could expect in the circumstance described. Good luck.

Warren

[kdd]

Thank you Warren