Removing Black Stains in Wood Furniture With Oxalic Acid

Intro: Removing Black Stains in Wood Furniture With Oxalic Acid

Iron oxide stains in wood are usually dark spots caused by prolonged exposure to water and / or metal. The iron oxide reacts with the tannins in the wood and stains it black. Wood can intentionally be stained black in the same way, and that's called Ebonizing.

Along the edge of my desk I kept a rusty metal ruler, and sometimes I would over-water the plant on the desk and the water would pool up under the ruler. In a short time this lead to black stains all along the edge of the desk.

I've seen some amazing results from furniture restorers using oxalic acid to remove such stains, but I couldn't find it locally and never got around to ordering it online.

One day I came across a How-To by Thomas Penrose and realized that I already had oxalic acid in the form of Bar Keeper's Friend. A big thanks to him for the write up. I'm going to relay those basic steps and add some tips of my own.

Materials and Supplies:

• Bar Keeper's Friend or similar powdered metal polish containing Oxalic Acid (Red Bear, etc.)
• Water
• Paper Towels
• Chip Brush (optional)
• Plastic Paint Scraper
• Stiff Nylon Brush (optional)

STEP 1: Assess the Stain

If the stain is dark, almost black, chances are it's from water exposure, but it could also be from ink etc.

If the stain is dark red, it's probably from wine or food or anything else.

This method will only work to remove dark iron oxide stains. It won't hurt to try, but it'll probably be more effective to bleach / sand / refinish other types of stains.

If the wood has a polyurethane finish or other surface coating and you see a stain, it's stained underneath, and that coating needs to be removed first.

If the piece has an oil finish or if it's raw wood, you don't need to do anything to prep the surface.

STEP 2: Make a Paste With Bar Keeper's Friend and Water

Add some water to Bar Keeper's Friend until you have a consistency that you can work with.

The ratios aren't important, but you don't want it to be too wet. Excess water is just going to raise the grain. All you need the paste to do is sit on the surface of the wood. You don't need it to soak in.

STEP 3: Wipe It On

Always test on an inconspicuous area first!

• There shouldn't be any negative effects, but it's good to find out on a small area instead of the whole surface if there is.

For the first application, target the stains.

Wipe or brush it on and then wait until it dries (15-30+ minutes).

As it's drying, you should see the white paste turn slightly yellow. This is good.

STEP 4: Scrape It Off

I scraped the dried mixture off and vacuumed it up rather than wetting the surface and wasting paper towels.

After the first application you should already see a huge difference. If not, then this method probably isn't going to work on the stain.

STEP 5: Second, Third, Fourth Applications

Mix up another batch and apply it the same way you did before.

When the stains are mostly gone, you'll notice that the area you cleaned will be lighter than the surrounding areas.

For the next application apply the mixture to the entire surface of the piece to help blend it together.

STEP 6: The End Result

I only needed 3 applications to get the stains to a point where I didn't mind anymore. Further applications will remove the stain completely. My plan is to refinish the top of the desk at some point, first by applying oxalic acid to any other stains, and then rubbing with #0000 steel wool and oil to clean the dirt while leaving most of the patina that's built up since I've owned it.

Final Tips:

• Because Oak has a very open grain, a lot of the mixture will be stuck in the grain of the wood. I used a stiff nylon brush in a circular motion to remove it. This probably isn't necessary on other species of wood.

• If your refinishing process involves steel wool, be really careful to remove all of the metal shavings from the surface, especially with Oak. It's recommended to use brass wool or synthetic wool to avoid this. When the metal particles get wet in the future, it will just start the whole staining process over again and you'll have to redo it. In practice steel wool is fine, just make sure to blow the piece off with compressed air and buff it with a microfiber to remove all of the shavings.

• When sanding, don't sand too deep. As you cut further down into the surface you might expose more of the stain, and then you'll have to reapply oxalic acid all over again.

Comments

[trishkinter]

Wow!!! This worked !! I have been trying to get a black stain out of an old dresser and nothing worked until this !! Thank you so much !!

[Lf]

We have a red oak countertop that has been finished with Watco butcher block oil and finish. Our well water (iron rust+) leaves dark, inky spots on the wood almost instantly. What is the best way to
prevent the water from penetrating the wood and avoid getting the spots in the future after we remove them? Any special coating that you recommend?

[jayphansen1]

You mention: If the wood has a polyurethane finish or other surface coating and you see a stain, it's stained underneath, and that coating needs to be removed first.
Question: what's the best way to remove a clear, satin finish on light colored oak flooring?

[david haimson]

I used Barkeeper's Friend on the top of an oak dresser. It took the iron stains out perfectly, but left a residue of white grit in the open pores. I took the top off the dresser, took it outside, and scrubbed it with dish detergent and water and a nail brush. Then I hosed it off thoroughly (using the "jet" setting), dried it off, and reassembled the dresser. Worked great, but next time I think I will make a solution with some oxalic acid crystals – easier to remove!

[resamaggiematt]

Hey so I have either water stains or dog pee stains on my floor that I found under my old rug. And I’m just wondering if this method would work for my hardwood floors? Thanks!

[PennyC55]

I used hydrogen peroxide the first time sanded it and it went away the second time here which I didn't think whatever happened my bad it was water and I want to go out and get Bar Keepers Friend and try it instead of using hydrogen peroxide.

[marcusarchitect]

Thank you for taking the time to explain this! You saved my jon boos butcher block island!

[rebagogo]

Thank you! You just saved a Heywood Wakefield Gate leg table. I do appreciate it!!!! AND I love Barkeepers Friend even more now.

[FedexM]

Thanks for the recommendations, here the result using acid oxalic at 8% .it is a new deck and the wood was in the water in contact with the rain appearing the stain everywhere

[mobdesign]

Thank you for this great advice. Two days ago I was sanding down an old maple chair with steel wool under a covered porch when the fog rolled in. The chair got damp, but I didn't think that would be a big deal until, a day later when all the newly sanded areas were covered in black spots. First I thought it was mold, but it didn't come off with bleach, peroxide, or sanding. But I wiped it down with liquid BarKeeper's, which I happened to have on hand, and black spots almost entirely removed after 5-10 minutes. Now I remember reading that steel wool should not be used on outdoor wood furniture, because even with good cleanup, the fibers of the wool get into the wood and oxidize, causing permanent black discoloration, so I was very relieved to find this solution.

[SusanB324]

I have to say this technique was truly AMAZING! I did some canning last weekend and put my case iron skillet on the table next to the cooling rack forgetting that sometimes they leak. When I went to move it a few days later the cast iron skillet was stuck to the table and had left a HUGE 12" black circle a few inches wide where it had sat. I quickly tried a few other things which took some of it off but not much so I Googled and found this tip. No more ring and practically no effort. Wish I had taken a before picture but this is the finished product. I have taken added a picture of the bottom of the pan. See the rust that is how big the stain was on the table.

[MissyL13]

Hi. Great tutorial It totally worked but the black on my counter has come back. Any advice on how to keep it form coming back? I have done it twice now and the stains just keep appearing about a week later.

Thanks,

Missy

[dlager]

Wish I had seen the lemon juice idea first. A lot of powdery residue got stuck in the oak grain of the table leaves I was working on (not the main table top for some reason). Maybe it was because the grain on the leaves was more open due to stripping off the varnish right before applying the Bartender's Friend. I plan to continue trying mineral spirits or water and a stiff brush to dissolve or brush it out. It is not coming out easily. If I can't get it all out, will it cause a problem with staining and varnishing?

[dicandoit]

Thank you! Helpful advice! Does anybody know how to get Chocolate wine off a log home cedar wall? I bought it this way, I didn't get to drink any of the Chocolate wine!!

[DRAGUA1979]

Follow the grain with the brush as well so you don't tear up the wood.

[sunspotbaby64]

regular clorox bleach will remove the stain.No matter what you use though,you will have ti restain the the wood.After bleaching the stain damage,you need to rinse the wood really good with water.Let dry a few days.Sand and then stain.Then put on a sanding saler,sand,then apply two finish coats of polyurethane

[Evelyn348]

timely advice, I have wooden clothing racks for drying clothes outside and was wondering what I would need to do.

[ooohlaa]

we all have to remember to choose the least toxic method for all approaches to life's problems, i.e., start with lemon juice ... it might take a few doses but better not to breathe fumes of anything, we already do from outdoor air, to public bathrooms, to department stores, to golf courses etc. we are always breathing in toxicity. that being said I would use this method and am grateful for it, if must be! thanx

[foobird]

Take care when using Oxalic acid. It is poisonous.

[momoluv]

I didn't even know those stains could be removed! Great job :-)