Difficult stain on oak top

Oxalic acid might be the answer, it's certainly the way to fix stains caused by iron/rust in oak. Rhubarb leaves contain oxalic acid but I think you can buy it in a bottle specifically for clearing black stains on oak.

You would need to sand lightly to get to bare wood, then treat with dilute oxalic acid. (possibly several times). Wash carefully when done. Allow to dry, give a light sand to smooth any raised grain, then refinish with whatever you fancy.

Chris and John are right that the most common stain problem with oak is a blue-black tannin stain normally from ferrous metals but also caused by other things. The acid doesn't need to be Oxalic. Lemon juice or spirit vinegar will work.

Cover the stain with kitchen paper or cotton wool, saturate with your mild acid, then cover it all with cling film or polythene so that it doesn't dry out, and leave it overnight to work. Literally rinse and repeat if necessary.

TW

I sanded the residue from the rubber/plastic from the torch but it seems to have soaked into the oak.

My earlier attempts to lift it failed but created the dark stain on the oak. Today, I tried Bar Keepers Friend.

It seems to have improved a bit but there are water stains or residue of BKF remaining. I know if I try to wash that off it will go dark again. I shall hold a conference with SHMBO and determine the next stage.

Thanks for all your advice. Much appreciated.

Alan

Don't forget that you need a Home Office Explosives Precursors and Poisons Licence (EPP) to possess oxalic acid crystals or >10% solution.

Odd for something widely available on Ebay and many DIY suppliers...