enamel (v.)

"to lay enamel upon, cover or decorate with enamel," early 14c., from Anglo-French enamailler (early 14c.), from en- "in" (see en- (1)) + amailler "to enamel," variant of Old French esmailler, from esmal "enamel," from Frankish *smalt, from Proto-Germanic *smaltjan "to smelt" (see smelt (v.)). Related: Enameled; enameler; enameling.

early 15c., in ceramics,  "a vitrified substance, either transparent or opaque, applied as a coating to pottery and porcelain," from enamel (v.). As "hardest part of a tooth," 1718, from a use in French émail.