Case hardening
Also called: casehardening
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Case hardening is a drying defect in which the outer part of wood becomes drier and harder while the interior remains wetter. The uneven condition leaves stress between the outer case and the inside.
Outer case and interior
The hardened outer layer is called the case. The wetter inner wood is the core, the material inside that layer.
The defect
Case hardening describes unequal drying through the thickness of a piece. The name refers to the condition of the wood, not to a surface coating.