I have recently seen two different pieces of heavy glass—a Gunnel Nyman piece with interior bubbles from a spiked mold, and an Ingeborg Lundin Ariel—with massive cracks in them, but no impact point, indicating they had been dropped. And the pieces remained whole, cracks not withstanding. The cracks don't seem to show on the surface of the glass.
What causes this? Putting them in the dishwasher to dry? Inherently different tensions within the glass layers? An impact while being shipped, but while still wrapped (I have seen camera lenses smashed this way)?
Anybody else ever seen this? Any ideas?