Thread: Tough stain won't budge ...

Try a saturated solution of oxalic acid and when done, make sure you repeatedly wipe away the residue with a damp cloth because you don't want to sand or steelwool any dry residue.

G'day Wood,

Could you further explain the technique in more detail please? When you say saturated solution what exactly do you mean - saturated as in undiluted?

In regard to product ... what form of Oxalic Acid product should I be using? Is there a weaker product that is better for this job or should I stick with off the shelf stuff from the hardware/general purpose stuff?

In terms of application ... should I apply with a Q-tip very lightly? How much do I apply generally? I have no experience with Oxalic Acid so would appreciate guidance here.

Cheers, TR.

Oxalic acid is sold in crystal form. Oxalic is toxic, so under no circumstances sand or abrade the dry crystals because the dust will become airborn and will attack your nasal passages, which apart from being very unpleasant, is dangerous as the Oxalic will easily enter the bloodstream through the nasal walls.

Pour some boiling water into a glass or plastic container and slowly stir in some of the Oxalic crystals until no more will disolve (there will be a telltale amount of undisolved crystals at the bottom of the container). This is a saturated solution.

Depending on the size of the stain, use the largest possible brush to fill the area without going over the edges. Use a heat gun to re-heat the solution and drive it into the stain. Wipe the area with a damp cloth before repeating the process as that will be the best indicator as to how the process has gone. It may require a couple of applications to achieve the desired result. When you're satisfied the stain has gone, or has been appreciably minimised, wipe the (now crystal again) residue off the surface with a damp cloth and let it dry. Repeat wiping and drying until there are no crystals visible.

The remaining Oxalic solution can be kept indefinitely, but don't let metal get be contact with it (no metal jar lids). I find the Macona coffee jars with their glass/plastic lids are perfect. The solution will partially recrystalise as it cools, but you only have to stand the jar in some very hot water for a few minutes to revitalise it when next required.

I think I remember replying to your red stain problem.
Now, if it is the same person, you have a chemical stain problem.
Seems you have iron oxide (black stain) in your wood - very permantent.
If you can limit the working of the oxalic to just that one spot, it might help.
You say you have a small dip, that might be a good thing!
This dip might give you a place to use shellack sticks.
in the attached photo you see how to mix small amounts in a beer cap. Go one shade lighter than the desired color as the heating may darken the finished color.
Once you start using this contraption, you'll wonder how you ever got along without it!

Thanks Wood for your explanation!

Righten,

That was me mate with the red stain ... that one came out fairly easily with metho. It was not until I stripped the rest of the old shellac gunk back that I determined that this black stain would not move by normal methods - because this is maple veneer it stands out quite nicely.

I had actually given thought to filling over the little dish with putty but knowing putty filler I was dubious of how this might look unless done with great care and skill. I had not thought about using Shellac sticks though! I have used wax sticks before on gun stocks - where I have most of my experience in wood - but never seen Shellac sticks.

Do you have any before and after shots of shellac sticks used on light furniture I could get a look at? By the way, when you say a chemical stain, what would be the cause or source of such a thing?

Best, Tiki.

George Franks concocts a recipe of rust (iron oxide) and vinegar (acetic acid) to color, chemically, wood that has tannic acid in it. Walnut with Liq Nite. he calls 'poor man's ebony'.
Being a chemical stain, it very effective and non-fugitive (all the things you don't want!)
Shellack sticks melt at a pretty low temp. - as seen in the photo I provided, they all melted together under the Sun in my truck!
With a pair of needle nose pliers, I'll hold the beer cap (plastic seal removed) and mix my colors over the flame of my stove, 'til I am satisfied. Then with a plug in solder-like tip, melt a bit on the edge (load the tip) of it and 'spackle' your divot, cigarrette burn etc.
Get your finished color - proceed as though the surface were flawless - put a couple of coats on it and give it time to harden. Practice with the tool and some shellack and when you have the backround color established, go for it.
A pencil was provided with my kit, to draw in grain.
Make sure your divot, or low spot, is as large as the black spot.
It's late, or I would do a primer by photo for you. If you really want, I will do a photo lesson tomorrow.

A photo lesson would be great mate ... I'd like to see how you work with this stuff and the final look of it when done. Can you sand back the shellac sticks when they set?

Tiki.