Because the glass was not fully compatible. Only clear boro is 33 COE, when materials are added for color, it can become to far one way or the other and cause cracks. It could also be the blower did not fully anneal the piece.
Because the glass was not fully compatible. Only clear boro is 33 COE, when materials are added for color, it can become to far one way or the other and cause cracks. It could also be the blower did not fully anneal the piece.