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As above, its been used as a rain collection device for years and now id like to see its natural colour. Its quite black at the moment which i take it is ingrained mould. Ive tried a bit of household thick bleach which is quite good but not quite there...i need something with a bit more kick..acid?
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And buy industrial strength and quantities to use. It might do the job.
I have no idea where you'll get it from (rhubarb?) domestically but oxalic acid would do the job.
Wash well with sodium carbonate solution after to nuetralise it off.
And no kidding here - hydrogen peroxide, get a hair bleaching kit.
I think you might struggle. Any staining will go quite a long way into the wood. Be simpler to buy a newer/better one
Saccades has it. Oxalic acid, or rhubarb crystals. Ebay I think will be your friend there.