Glass coefficient, that's the word I was lookin for and the reason for the fractures (Akro superman, Akro indian Blanket) and a few others all have a similar problem because of the coefficient (incompatibility) of two different types of glass used to make them that cool @ different rates causing the fracturing so common to the type. I think all my Alley supers I have @ least one fracture except maybe one ?? The Akro Supers that I kept are about 50/50 and none of the blankets I have exhibit any fracturing ( not the first either) I had to pick a lot of cherries to get some that weren't split.