exploding glass

[MarthaB56]

Hi- Newbie here. Hoping someone can help me understand why my glass exploded when trying to make a pocket vase. I used a piece of 1" fiber board as the form for the pocket. Using Bulleye 90 COE. I have a Paragon QuickKiln 6 with a controller. I set the controller @ 1.5 and after 10 min I heard the distinctive sound of glass cracking. Suggestions/ words of wisdom to overcome this boo- boo?
thanks!

[Bert Weiss]

Fiber board is an insulator. It looks like you heated up to a point where the temperature gradient within one piece of the glass was great enough to cause a thermal shock crack.

[MarthaB56]

thanks so much for the fast response. I'll try using fiber paper next time.

[rosanna gusler]

fiber paper is an insulator too. you have to slow way down on those vases. also annealing needs to be longer. rosanna