Re: Removing stain from oak

That may be a problem; oxalic acid is unstable, it wants to stay cold (and of course, you have to handle it with glass or plastic, it gets poisoned in a steel or stainless container).

It makes iron stains go away by dissolving the iron, but you want to rinse away the solution or the iron comes back again when the oxalate destabilizes.

Rather than scraping, I'd use a chemical stripper. It's much easier, and finish penetration might defeat scraping.

Hello,

Oxalic acid is not really unstable. It has a melting point just above the boiling point of Water so hot Water should not be a problem. A solution kept at ambient temperature works just fine after several years.

I assume you mean that a hot solution "wants" to cool to ambient temperature. A hot solution will hold more of the acid than a cold solution. As the hot solution cools, the acid will crystallize. I have never found that to be a problem other than it leads to more dry crystals to wipe up after the iron has been chelated and the stain removed.