Iron Stain on Wood

Abstract

Iron stain, an unsightly blue–black or gray discoloration, can occur on nearly all woods. Oak, redwood, cypress, and cedar are particularly prone to iron stain because these woods contain large amounts of tannin-like extractives. The discoloration is caused by a chemical reaction between extractives in the wood and iron in steel products, such as nails, screws, and other fasteners and appendages. This often occurs the first morning after rain or dew, when water enables the extractives and iron to meet and react. For hundreds of years, ink was made by mixing tannin and iron in solution, where the reaction takes place instantly.

Citation

Knaebe, Mark. 2013. Iron Stain on Wood. USDA Forest Service, Forest Products Laboratory, FinishLine, 2013; 2 p.