I agree with the above response. If this is helpful here is what I pulled off another site a few years back and have used this process as a reference.
Ok, first things first. This is an Oxalic Acid bath "how to" post. This isn't an "Oxalic Acid-is-the-best-way-to-remove-rust-and-all-the-other-ways-suck" post. I know there are other ways to remove rust from parts. Citric Acid and Vinegar baths are the other two popular ways that have been documented in the museum. There are others as well. If those work for you, great! I'm not disparaging any other ways to remove rust. As previously stated, I am merely documenting how to do an Oxalic Acid (OA) bath. So, I am asking up front to not comment on any other ways to remove rust in this thread. If you do, I will instantly make fun of you and your bike(s). Of course, all in the name of good fun and cheap entertainment. Enough with the preface, let's get started.
Expectations
You can expect clean parts if you do the bath correctly. It takes a good amount of time to complete a bath. At the solution strength I use, it usually takes over 24 hours. If you want to sit and watch it, you need to have a plenty of beer. I think this would be slightly more interesting than watching you wife's "how to scrap book" video. All of the after photos you will see are of parts that had no polishing done to them. I only rinsed them off and dried them with a soft white t-shirt. After you use the OA bath, you will need to put your parts in a controlled environment. If they remain in a harsh environment, the rust will return.
How do I handle/treat Oxalic Acid?
Like you would with any other chemical or cleaner: carefully and with caution. Do not ingest or inhale the OA crystals. Wear gloves to prevent skin irritation. Use it in small amounts. Always replace and make sure the lid is secure on the OA crystal container. Do not splash the OA solution after you mix it. The strength at which the solution will be used is going to be weak. Much weaker than a liquid deck cleaner. However, still use it carefully. I would also make sure that kids or small animals can't get around it. When finished, I pour it in the yard and run water over it. I think it actually helps the grass. It sure doesn't harm it.
I have read the MSDS on Oxalic Acid crystals. Although Oxalic Acid is a natural occurring substance that is found in many vegetables, in crystal form, it is much stronger. Remember, we are disolving a small amount of OA crystals into much higher volume of water. This makes a highly diluted liquid. As I stated above, always use caution when handling it.
What kind of parts can I put in an Oxalic Acid bath?"
Steel or Chromoly. I only use OA on chromed steel parts. I would not use it on Aluminum or Black Oxide parts. It will jack up black oxide parts, because it is trying to remove the oxide finish. Here are some seat guts I did to show how they will turn out. So, if you have a chromed 4130 or chromed hi-ten steel bike, you have the perfect candidate for an OA bath. You can use OA on bare steel but it will flash rust. The parts I am using for this OA bath is a set of Robinson forks, handle bars, a rusty stainless (it is stainless, not stainfree) chain and a set of Profile Cranks. I need to thank 71bike for letting me soak the forks after he paid for them. He was more than gracious and actually encouraged it. I'm not sure how many people would do that.
Since you have the parts that need to be cleaned, you now need to go get some supplies.
1. Plastic Container- This is the main item you are going to need and it needs to be ideal. I use a plastic "under the bed" clothes container that comes with a lid. It works great and the lid keeps pets and kids out of the bath. I believe I purchased mine at Walmart for around $20. The size or volume of the container is a 66 qt/ 62 L. I can put a frame, bars, forks, and most of the other chrome components in it. A rear dropout does stick out of the water surface, but I overcome that by just flipping the frame. If you are trying to do a couple of small parts, of course a smaller container can be used.
2. Scotch Brite pads (NON-SCRATCH type)- Since you are at the store, go ahead and go get some non scratch scotch brite pads. If they have the white ones, these are even better. Do not use the maroon or normal green ones. They will scratch the surface.
3. Rubber Gloves- You don't want your hands to smell like OA. It could also be a skin irritant to some.
4. Old tooth brush(s). You will need these to get into small cracks. If you don't have an old one, then buy yourself a new one. Take your old one into the garage.
5. Oxalic Acid- I like using OA crystals. The crystal form is more economical than liquid deck cleaner or a prepared liquid solution. I purchased these two containers from a Sherwin-Williams paint store. As the container says, they call it "wood bleach". I believe I paid around $8.00 per container, but that was over a year ago. I'm not sure what the current market is for Oxylic Acid.
6. Rust Inhibitor- after an OA bath, you will need to coat the inside of the frame, forks, bars, and parts with a rust inhibitor. I like using LPS 3. You can find it online or at your local industrial supply store like Grainger.
So, you have your rusty bike taken apart and you have your supplies that your wife keeps asking, What are you going to do with that stuff?" You tell her, I'm going to go work some magic."
Prepping
To make sure your magic works great, you need to remove the dirt & grease from the parts. I like using Simple Green. It doesn't react to the OA. Of course, I thoroughly rinse off all the parts after I clean them. Does it seem weird to clean rusty parts? Maybe. But we are trying to remove 20 years of rust with an OA bath, not 20 years of rust, dirt, and grease combined. I would stay away from any cleaners that use bleach or other chemicals because the warning on the OA container says to stay away from them. As far as decals, I don't do anything to them. I just leave them alone. The OA bath will not harm them. I have never had an issue with factory decals. However, I have never done an OA bath with any custom made decals. I have no idea if an OA bath would harm them.
The OA Bath
Put all the parts you want to soak into the container. Now, fill the container with water. With my container, I can't fill it all the way up because there are small holes where the lid clasps are inserted. Look out for things like that. After you have the right amount of water in the container, it is time to add the OA crystals. I usually do the OA baths in my garage. When I add the crystals, I usually have the door closed and the fan turned off. I don't want anything blowing into my face. I usually like making the solution weak at first. It is always easier to add OA later that is what I did in this case. After I add the crystals, I usually put the lid on the plastic container. I then turn on the floor fan so it is blowing towards the garage door, and raise the garage door about 6 inches- a true 6 inches.
Mixing the solution
While wearing my rubber gloves, I open the OA container. For an effective bath, I usually add about three heaping tea spoons (or a table spoon) of the OA crystals. I use my gloved hand to gently mix the solution.
After making the solution, I usually wait six hours. If I don't see any reaction in six hours, I add a tea spoon. The reaction to be looking for is the formation of a yellow looking substance. After 12 hours, if you still aren't seeing the yellow substance forming, add two tea spoons. The solution will be strong enough if the solution has a slight sulfur smell to it. If you don't know what sulfur smells like, then think about a weak rotten egg smell. Instead of just waiting for the yellow substance to form, you could gently wipe the parts with the scotch brite pad. If you are able to wipe away some of the rust before there was the yellow substance formed, there is no issue with that. This is what happened to the Robinson forks.
Checking the parts
As I just stated, what you are looking for is the formation of the yellow substance on the part. When you see this, just gently wipe it off. I do this with the part still in the bath. If you see this substance, DO NOT LEAVE IT ON THE PART! Wipe it off! If you allow the yellow substance to stay on the part and turn a reddish-brown color, you will have a hell of a time removing it. This is why I mix my solutions weak and strengthen them as time goes by. The weaker the solution, the slower the yellow substance forms. Remember, this is not a race. Get in your head that this will take a long time. There is a payoff for your patience. Areas you want to check are areas that the chrome plating will be the thinnest. This is usually at bends, welds, and tight spots, like the chain and seat stays. I usually use the old nylon tooth brush to address these areas. Also look inside the bar-ends, seat post tube, and fork steering tube. All of these areas should have the yellow substance inside of them. I usually just roll up the end of the scotch brite pad, shove it down into the part, and turn it around. As you start to see the rust removed, keep the parts soaking.
When to stop
After about a day, you should see a vast improvement. If you don't see a lot of rust removed, then you need to strengthen your solution. When the parts look free of rust, I usually let them soak four more hours. This is to make sure that all of the rust has been removed. If after four hours, I still do not see the formation of a yellow substance, I take the parts out of the bath.
Finishing the parts
Take your parts and rinse the the surface and inside of the tubes with tap water. After you rinse the the parts, you can hang them so the water drips out or use an air compressor. On frames, because of the the different angles of the tubes, I usually put the frame on the bike stand and use my air nozzle to blow air into the weep holes. I have found it isn't exactly necessary with handle bars and forks and other small parts. I usually position them so the water just drips out. When I put the LPS 3 in, I usually start with the weephole higher than the rest of the part so gravity can do the work. This will displace any water that is in the tubes. So, after you rinse the insides with water, spray the insides of your parts with rust inhibitor. If you are going to get your parts powdered, you may want to talk to your painter about this. He will have to burn it out to make sure it doesn't come out of the part when the paint is being baked. My painter had to do this. If it is going to be sometime before the paint, you may want to go ahead and spray the rust inhibitor into it, but tell your painter about it. To spray it into the parts, attach the nozzle tube to the spray can, insert the tube into a weep hole, and spray. Then slowly rotate the part to make sure the entire inside gets coated. If any LPS 3 gets on the chrome surface, wipe it off. Do not allow it to dry on there. You will have some time to do this, it doesn't dry immediately. (In one of the after pictures, you can actually see some that dripped down the right fork blade. It just wiped off with no issues.)
After the LPS 3 gets sprayed inside, wipe off your part with a soft cloth. Then take it into the sunlight or a bright light and admire your work. If you want to take it to your wife and show her your "magic" , feel free to do so.
