vitrify

verb

1. (transitive)To convert into glass or a glass-like substance by heat and fusion.
2. (intransitive)To be converted into glass, especially through heat.

   “A large percentage of all Late Horizon fragments at this site was overfired, to the point where many were vitrified, black to dark brown, and misshapen, some with blistered surfaces.”

   “Her work was endless, she carried tubs and cauldrons and pails of heat-blasted sand, sand blasted into liquid glass, up the ladder that had vitrified where her bucket splashed, and tipped the liquid glass into the swimming pool, where, at the touch of the water, it turned into her huge, solid tears.”