moomba
N/A
Oxalic Acid, the active ingredient in Y10 and other cleaners, should do the trick. Cheap and widely available on the Internet. Handle with care though and look into safety instructions before use.
+1 for oxalic acid in its pure form diluted as recommended , took out all black stains in my teak all inside then sanded and varnished , need to be carefully for an even layup
this is not a man made chemical but natural product so should be ok on your wood,
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