Once my back is healed up enough from back surgery where my wife :) and my doctor are satisfy enough where I can tinker around the woodshop again I have a project where I have alot of grooves and cuts that need to be cleaned of old stain but cannot afford to have it done commercially so wonder how good oxalic acid is. Now I dont care how long it has to stay to get te job done and bleaching the wood is not a big concern but how good is it really? I miss the stuff that uncle sam took away. And soaking the wood be better or just wipe on and let it sit?
Oxalic acid bleaches the wood. It does a good job for me. For stripping wood of varnish, lacquer, or shellac finish, use a stripper first. Either a commercial stripper or a homemade stripper of either TSP or lye.
Then, if stains remain, use oxalic acid. Oxalic acid is particularly good at removing black/brown tannin stains in oak and other woods with tannins. But it works well overall to remove other stains, including those applied stains.
Regular household bleach can also be used to bleach wood, but I find oxalic acid to be more effective and requires no neutralizing after use as does bleach.
While applied finishes have new names, there's not much that has changed in finishes in 100 years, particularly in removing them, though in many cases the strippers are now underpowered.
Oxalic acid is just another tool in the arsenal.