To lighten wood, your best bet is to use a "wood bleach" kit.It comes with two bottles A & B (sodium hydroxide & hydrogen peroxide)
Oxalic Acid is commonly sold in hardware stores as a stain remover ,most often used on old decks.By stain remover ,I mean from nails ,screws etc. and dark stains in high Tanin woods,such as Oak.But as a general bleaching compound to lighten wood ,the wood bleaching kit is your best bet.
Do a search in woodworking sites to locate the product.
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