A cosmetic defect in timber where the sapwood turns blue, gray, or black due to the presence of microscopic fungi. The fungi are typically introduced by bark beetles attacking dead or dying trees. While it does not significantly reduce the structural strength of the wood, the discoloration degrades the visual quality and lowers the commercial value of the lumber for appearance-grade applications.
Heard on the job
The mill docked our pay on that last load of pine because it was riddled with blue stain.
Also heard as
- sapstain