Vitrification in ceramics is the formation of glass through the melting of compounds.  In this article researchers found vitrified remains encrusted the surface of Vesuvius victim's skulls.  Kind of disturbing but interesting.
https://www.nejm.org/doi/10.1056/NEJMc1909867  

​We took the boys to the Museum of Fine Art in Boston @mfaboston. We got to see their awesome collection of Kandler porcelain pieces. (If you don’t know the story of Meissen porcelain, check out The Arcanum by Janet Gleason). This piece was particular my interestingly as you can see the interior, and thus the raw clay. You can see how much heavy lifting the glazes are doing to convey the whiteness of the work. While in reality they porcelain is not particularly white.