Tempering

From the Merriam-Webster Dictionary:

1-3a : the state of a substance with respect to certain desired qualities (such as hardness, elasticity, or workability)
especially : the degree of hardness or resiliency given steel by tempering

2-2a : to anneal or toughen (glass) by a process of gradually heating and cooling
b(1) : to harden (a material, such as steel) by reheating and cooling in oil
(2) : to soften (a material, such as hardened steel or cast iron) by reheating at a lower temperature

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