glassen vs vitrified

glassen

adj
  • Resembling glass; glassy; glazed. 

  • Made of or consisting of glass. 

verb
  • To coat or cover (e.g. pottery, etc.) with glaze; make glassy. 

vitrified

adj
  • Converted into glass. 

How often have the words glassen and vitrified occurred in a corpus of books? (source: Google Ngram Viewer )