Ramping up too fast?
I have a tendency to ramp up too fast…
I see that your project is a single thickness of glass, but it’s 1/4" Personally, I would slow it down. I used to ramp everything about 400-500° per hour, but had a lot of problems with large bubbles, but never thermoshock.
I’m not a lot more conservative in my firings (thanks to Karen and Paul!) and have had much better success.
I haven’t done freeze and fuse, but I would probably go a little more conservative on your ramp up.
Good luck, and post a picture when you’re done!