Tannic acid stains in oak

October 16, 2000

by Professor Gene Wengert

What residue might be in oak furniture that would react with trisodium phosphate to turn the oak purple?

TANNIC ACID in oak will react with iron to form iron tannate. Perhaps there is iron in the water, the bucket is rusty, or ??? The stain can be quickly removed with a weak solution of oxalic acid.

Professor Gene Wengert is Extension Specialist in Wood Processing at the Department of Forestry, University of Wisconsin-Madison.

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