Woodworking Talk banner
1 - 20 of 21 Posts

·
Senior Member
Joined
·
7,222 Posts
Discussion Starter · #1 ·
After reading EricD's post on oxalic acid for rust removal, I decided to give this a try. I purchased a small container of wood bleach at a local hardware store, for a mere $8.

Took awhile to find it. In this store it was with the wood stains/solvents etc and not the cleaning supplies.

I read on this site to use a 5% solution. This felt like too much.
http://oxalic-acid.info/oxalic-acid-rust-remover

I read on another site to use 1 tablespoon per gallon, which is what I used.

EricD mentioned about keeping the solution warm.

For the first round I mixed the oxalic acid in hot water and left the items overnight. The rust was mostly removed. I did not have a white or black patina. The solution was a slight green colour.

For the next round the solution was now room temperature, about 65 deg F. I had the solution in a zip lock bag since I did not have a suitable container.

I decided to use nature to warm up the solution so put the zip lock bag in a black plastic paint roller tray and laid this on a stool in my sunroom in the morning.

When I removed the items later in the afternoon I saw there was white particles in the solution and on the metal. This was not a patina and just washed off.

Today I tried round three. Again leaving in the same solution with the white powder, but only for a few hours.

The metal had a greenish coating which washed off. Some of the metal had black patina which I had to work on with wet-dry paper to remove.

One mark puzzled me. It was on the edge of a plane blade I had sharpened the day before, so this edge had no rust.

I thought oxalic acid only worked on rust.

So anyone have any comments on what I may have done wrong?

Too much heat, wrong solution, or just my bad luck?
 

·
Log dog
Joined
·
7,933 Posts
I'm interested to find out how this works Dave.
As to a secondary rust removal. I'm happy how electrolysis worked, but would like to see what the two differences are.
 

·
Senior Member
Joined
·
7,222 Posts
Discussion Starter · #4 ·
I'm interested to find out how this works Dave.
As to a secondary rust removal. I'm happy how electrolysis worked, but would like to see what the two differences are.
From what I have read on the forum and elsewhere, electrolysis is preferred when the finish AND rust need to be removed. Very inexpensive method as you can attest.

The bicycle crowd seem to like oxalic acid because it is inexpensive, so they can dunk entire frames in the solution and it does not harm paint or especially chrome.

Evapo-Rust also does not harm paint or chrome, but it is expensive. I think this is the old stand-by when the finish needs to be kept and the parts are small enough so the cost of the Evapo-Rust is not a factor. I found using ziplock bags helped me to minimize the volume needed.
 

·
Senior Member
Joined
·
7,222 Posts
Discussion Starter · #5 ·
Was rust removed?
Yes. In today's round the items had somewhat superficial rust. Deeper in some areas, but not deep pitting.

I had only left in a few hours since it became cloudy.

As I cleaned off the patina, there was some underlying rust on one side of the blade.
 

·
Registered
Joined
·
42 Posts
Sounds as if it worked. The cold temperature cause it to fall out of solution, I think 658F is too cold, I use minimum 80* (fish tank heater temp) and start with hot tap water. I try to watch the process closely to pull the object before the white residue coat happens.
 

·
Senior Member
Joined
·
7,222 Posts
Discussion Starter · #7 ·
Sounds as if it worked. The cold temperature cause it to fall out of solution, I think 658F is too cold, I use minimum 80* (fish tank heater temp) and start with hot tap water. I try to watch the process closely to pull the object before the white residue coat happens.
How do we know when the solution is spent?

Any comments on the black patina. Harder to remove than the Evapo-Rust grey patina.
 

·
Log dog
Joined
·
7,933 Posts
Dave Paine said:
Oxalic acid is likely called "Wood bleach" on the container.

I found it at a local True Value hardware store, but likely in most hardware stores or the big box stores.
Thanks Dave. Just don't lick or drink it.
I'm sure you wouldn't but when I look at the definition on it it says its poisonous.

Text Font Document Paper
 

·
Registered
Joined
·
42 Posts
I'm not sure what the black patina is. I haven't had any issues but I always sand bare metal with 400 grit 3M paper so that may be why I haven't noticed it. Fatal dose of wood bleach is ~60gms for a 220lbs person, about the same as Clorox, slightly worse than salt, be careful not to eat or drink it!
 

·
Registered
Joined
·
1,899 Posts
Oxalic acid source Cheap!

I lived on my wifes sailboat at a marina, that had showers. The plastic shower stall would get iron stains form the well water. I found out that by spraying on oxalic acid, mixed with hot water, the stains disapeared as you sprayed.
I tried it on metal, and had good results.

Here's the best part. I found a swimming pool supply co. where I bought 50#'s of oxalic acid for $55. Other folks at the marina split the purchase.
That was when 1# at the store was about $6-$7.
 

·
Premium Member
Joined
·
6,338 Posts
No refinisher should be without it.
You know the old black rings that are found on a lot of antique furniture that were made from metal cans sitting on the surface? These rings occur when steel or iron gets wet and comes in contact with a wood that contains tanic acid such as oak. The tanic acid in the wood and the metal form a black dye which seem almost impossible to remove.
To remove these rings, make a thick paste with oxylic acid and water. Then paint this paste thickly on the rings. Place a damp cloth on top and use a clothes iron with moderate heat on top of the cloth. Check from time to time and make sure you are not burning the wood with the clothes iron. This will work about 80% of the time.
 

·
Registered
Joined
·
114 Posts
oxalic acid

I restored an old buffet that was in my mother-in-laws basement. It had a huge black spot on one end that was always covered up. The buffet has a veneered walnut top. I just followed instructions on the container and it worked beautifully. No issues with the veneer. After I got it all cleaned up I restained it with walnut stain and then a coat of amber shellac. I used a fresh can of shellac, siphoning off the top and not stirring up the wax in the bottom of the can. Then a coat urethane. Nobody wanted it and it was the last thing left in the house. Now they think I'm a miracle worker.
 

·
Registered
Joined
·
1,160 Posts
The primary use of oxalic acid is to remove mineral stains from wood and some other materials. Water stains on wood, particularly woods high in tannin. Oxalic acid does a good job removing black metal stains.
 

·
Registered
Joined
·
17 Posts
Dave Paine

If you are dipping parts to get rid of rust? Here is what I do to clean hinges and part with. I use a muriatic acid solution from the hardware store (not the premix). You will need a lot of ventilation and use a Rubbermaid tub. some other types melt after a while with it. I use 1 part acid and 4 parts water. Pore the acid in after you have the water in but use the corner to keep from splashing. Also have like tub of water to rinse it in. In the summer, most parts are ready in as little as 30 minutes. You can always redo the dipping. I use green pad and fine metal brushes to scrub with in the rinse water. Dry immediately completely, and some parts I use a hand torch or heat gun to make sure. Then you can polish and/or refinish.

One more thing. Muriatic acid removes zink violently bubbling. Do not be close by until it stop. Just be safe, the fumes will hurt you and don't breath over the acid tub for any reason and use protection.

Floyd
 

·
Senior Member
Joined
·
7,222 Posts
Discussion Starter · #19 ·
The oxalic acid is not a dipping method, rather submerging the parts for an extended period of time.

The oxalic acid is not as difficult to handle as muriatic acid but does a good job when the parts are left for long enough perioid.

Rust removal is not the intended use of oxalic acid, but it is effective.
 
1 - 20 of 21 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top