25. Solving a chemistry problem

10. In one of the books of the doctor metallurgist Georgius Agricola (1494 - 1555) it is told how a skilled glassblower made two vessels of transparent glass. He lowered the red-hot vessels into a vat of cold water. One vessel immediately shattered into small fragments, while the other remained intact. The master donated the amazing vessel to the Hanseatic League of Cities, where the work of glass-blowing art was kept for a long time in the town hall of Hamburg. Many doubt the possibility of obtaining thermally stable glass at that time and consider this story unlikely. What substance did the glassblower use to make such an unusual vessel?