THESAURUS
anneal, brutalize, calcify, callous, case harden, cornify, firm, fossilize, harden, indurate, inure, lapidify, lithify, petrify, steel, temper, toughen, vitrify
ROGET THESAURUS
Hardness
VB
render hard, harden, stiffen, indurate, petrify, temper,
ossify, vitrify, accrust.