Source : Webster's Revised Unabridged Dictionary (1913)

Devitrify \De*vit"ri*fy\, v. t.
   To deprive of glasslike character; to take away vitreous
   luster and transparency from.

Source : WordNet®

devitrify
     v 1: become crystalline
     2: make (glassy materials) brittle or opaque
     [also: {devitrified}]