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    Author(s): Mark Knaebe
    Date: 2013
    Source: USDA Forest Service, Forest Products Laboratory, FinishLine, 2013; 2 p.
    Publication Series: Finishlines
    Station: Forest Products Laboratory
    PDF: View PDF  (162.48 KB)

    Description

    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.

    Publication Notes

    • We recommend that you also print this page and attach it to the printout of the article, to retain the full citation information.
    • This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.

    Citation

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

    Keywords

    iron stain, iron, wood, discoloration, extractives, oxalic acid

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https://www.fs.usda.gov/treesearch/pubs/48449