Finish checking

The fine network of hairline cracks that appears in a lacquer finish as it ages, shrinks and loses flexibility.

It is a physical failure of the coating, not of the wood, and it happens when the finish becomes brittle enough that temperature changes make it crack along stress lines. Nitrocellulose is far more prone to it than modern catalysed finishes, which is why old instruments and deliberately aged ones show it and newer ones usually do not. Cosmetic on its surface, deep checking and the shrinkage that accompanies it can let moisture reach the wood, and it reduces resale value unless it is considered desirable ageing.

Example: a guitar moved from a warm room straight into a frozen van will often come out with fresh checking across the top.

Finish checking

See also