an·neal 
(
ə-n
ēl
)
v. an·nealed, an·neal·ing, an·neals
v.tr.1. To subject (glass or metal) to a process of heating and slow cooling in order to toughen and reduce brittleness.
2. To strengthen or harden.
v.intr. To become strengthened or hardened: "the time she needed for opinion to anneal around her policy" (Alexander M. Haig, Jr.)
[Middle English anelen, from Old English onǣlan, to set fire to : on, on; see ON + ǣlan, to kindle.]