Hi, I've bought a few slabs of sawn oak from a mill to use as shelving. They've got brownish tide marks which I know are tannin stains, I thought it wouldn't be too much bother to shift them. So far, I've had a go with oxalic acid which has kindof worked but there's still noticeable marks. I was wondering whether would putting them through a planer work? As in, would it reveal a fresh surface? I ask as I don't have a planer, or does anyone have any other ideas to remove them? Thanks alot.