Probably a mild acid. Vinegar, soda water, things like that. Then neutralize the acid with a mild base, like baking soda in water, or just rinse thoroughly in water, dry the object, and oil it to prevent further rust.
Muriatic acid, a moderatly strong acid, is used to adjust pH in swimming pools, diluted with water it can be used to remove rust. It can also be dangerous to handle. Enough baking soda will also neutralize it. This was the first thing I learned to use, when I started metalworking. It isn't safe to use, but you can take precautions to keep yourself safe.
Phosphoric acid is often used. It is the active ingredient in Naval Jelly. Also a component of Coca-Cola.
Some use Citric Acid. It's a mild organic acid, and works slowly.
Some use Sulfuric Acid, or Nitric Acid, which are strong acids. Combined in the right proportions they will disolve gold. This is the Aqua Regia of the old metalworkers and jewelers. LOTS of baking soda to neutralize! Individually, and diluted, either can be used with jewelry metals, copper, brass, and bronze as a pickling solution to remove fire scale. They can be very dangerous, too.
For rust, specifically, any of these will work. The milder acids are safer and easier to use, but take longer.
There is also electrolytic rust removal. You can use baking soda, washing soda (sodium carbonate), or lye (sodium hydroxide) with a source of DC electricity to remove rust from steel and iron. It will also disolve non-ferrous metals. Baking soda is a mild base, washing soda is stronger, and lye is very strong, enough so to be dangerous. I prefer washing soda. Unless your skin is very sensitive, you can get it on your skin without suffering serious damage, though you'll want to wash it off as soon as you can.
You can also buy solutions made specifically for removing rust. My personal favorite is EvapoRust. It's not cheap, but it is good. It's also safe to handle, and non-toxic. Metal Rescue is another that I've tried. I don't think it works as well, but that may be a problem with the way I used it, or what I was using it on. It was a bit cheaper when I got it. You'll have to figure out which one (or ones) work best for you. For these, you clean the oil, grease and loose rust off the object, then immerse it. Agitate it once in a while, and check it frequently. These do not harm other materials, like wood or non-ferrous metals. I'm in the USA, so what you have available to you may be different.
Bill
WmRMeyers,
The problem with Acids is that they remove sound parent metal as well. If you do not constantly monitor an item it is very easy to destroy it. Work well if used with care and hovered over though. Same with electrolysis as well, it can leave serious pitting and also needs to be set up so that the rusty surfaces are equally exposed to the cathode.
As I have said before I am a big fan of molasses as mixed up at 40:1 - 60:1 with water it is super cheap, effective and only attacks noncorrosive. Slow is its only drawback but the time depends on what the parent metal is and how bad the rust is. Benefit is you can throw stuff in a tank of it and just leave it.
Small delicate items can be de-rusted with strong Black tea, this is something that is used by museum curators.
Fluffle-Valve (Sep 9, 2021), suebob (Sep 9, 2021), WmRMeyers (Sep 9, 2021)
If it's rusted badly enough, anything, inclulding my fav, EvapoRust, will destroy it. Had a set of feeler gauges for auto tuneups that sat in a box in uncontrolled space for a coupld of decades. The thinner leaves were destroyed. Had to have been rusted through. I've never tried molasses, myself, and had never heard of using black tea, but it's a source of tannic acid, so can't see any reason not to use it. Though I'd have to buy Lipton's to try it. NOT using my Earl Grey for that!
With electrolytic rust removal, if you set up the electrodes correctly, the only pitting will be where the rust left pits, and on your anodes. OTH, if you set them up reversed, it will destroy your object. Found that out the hard way, one day, on a Schwinn tricycle frame when I was just starting with it. You can control the current, and that affects the speed of the process. For machine tools I use a 12VDC battery charger, and from 2-10 amps. For delicate stuff, which I've not done, the milliamp range is supposed to be very good. One of the smaller 12VDC wall-wart power supplys will do that. Just use iron or steel for the anodes, not stainless steel. The anode will be destroyed, eventually. And if you use stainless steel, you will create hexavalent chromium compounds, which is a hazardous toxic waste and bad juju.
Last edited by WmRMeyers; Sep 9, 2021 at 07:07 AM.
I too have used this method regularly first on tractor parts then tools and a couple of motorcycles and lately some old lathe bits.Great method of paint and rust removal on ferrous items as long as u are wary of hydrogen embrittlement common with all electrolytic processes in hardened and high tensile steels. only 3 volts is required but higher voltage helps combat resistance which steadily grows necessitating cleaning of electrodes
A light bulb and ammeter in the circuit to show current flow and bulb acts as a current limiter in the case of a short circuit,and after washing an etch coat of phophoric acid will eat of the black coating of magnitite leaving a passivated phosphate coating resisting rust if kept dry and is a great primer too
WmRMeyers (Oct 14, 2021)
Both of the battery chargers I use have built-in ammeters. I would think you could use the lamp instead of an ammeter. The meters have worked well for me, but it would be worth trying the lamp if you don't have one with the meter. I'll have to do that the next time I set up for electrolysis. Already having a meter would make it easier to see which is best, if there is one, and get an idea of how well it work just in case you need the other one. One of the things I like about this site is that it is possible to learn about a lot of stuff that very few folks have the time, equipment, and materials to try every thing!
Bill
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