Remove water stain from oak

We've got an old advertising piece from the days when Dad worked in the Whiskey bus. It's the end of an oak aging cask with a clock and some graphics, name of the company and Roman numerals for the clock numbers. Over the years of storage it got water stained. I'm not sure how the graphics were applied, decals, paint, whatever was used back in the day, but we want to preserve the graphics. The stain is not covering any of the graphics. So here's the question and I may already know the answer. Anyone know any way to remove water stains from from an unfinished piece of oak? I've done a little research, sanding, oxalic acid, but I'm not sure which is the best approach. Anyone have any experience in removing water stains? It may be that we photograph the graphics, sand the entire surface, take the piece to a sign painter and have the graphics reapplied, but that sort of destroys the originality of the piece.

This thread really needs pictures. Are we talking an actual water stain or a stain from iron or some other metal?

Thanks, John. Unfortunately I don't have the piece in hand. My brother has it, I'll see if he can send me a photo. Based on his conversation I'm pretty sure it's water and not a mineral stain. But let's see what happens.

I have had success removing water stains in unfinished red oak by wetting the entire surface uniformly with water and letting it air dry. YMMV.

You can even up the stain by using a stain on the rest of the surface. Golden Oak stain will give a more uniform patina to the whole piece. You may have to use artist brushes to get the proper stain.

IMO removing the existing stain is problematic no matter the method. There's just not enough control.

The other way may be to use a card scraper and remove most of the surface stain in very small areas. Again with out a picture, it's hard to give effective advice.

I have no idea if this is true… but I heard that lemon juice works.