Too little heat, or too much, and the result would not set properly: The glaze or color might peel, craze, bubble, or devitrify.    From Wordnik.com.  [The Creation of Color in Eighteenth-Century Europe] Reference

English experimenter will probably prefer to use English glass, and, if he is wise, will buy a good deal at a time, since it does not appear to devitrify with age, and uniformity is thereby more likely to be secured.    From Wordnik.com.  [On Laboratory Arts] Reference

Long-buried glassy lavas devitrify, or pass to a stony condition, under the unceasing action of underground waters; but their flow lines and perlitic and spherulitic structures remain to tell of their original state.    From Wordnik.com.  [The Elements of Geology] Reference