hardening (
http://definr.com/hardening)
n 1: abnormal hardening or thickening of tissue
2: the process of becoming hard or solid by cooling or drying
or crystallization; "the hardening of concrete"; "he
tested the set of the glue" [syn:
solidifying,
solidification,
set]
3: the act of making something harder (firmer or tighter or
more compact)