This is a cutNpaste of an article that I saved. It's a good read and credit belongs to the author...
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The Electrolytic Rust Removal FAQ
By Ted Kinsey
Recently on the Internet, there was a series of e-mails on the Clocks mailing list about rust removal from steel parts. These techniques are not necessarily the ones put forward by the BHI, but they do give very sound ideas on the technique of rust removal
What is the method?
A technique for returning surface rust to iron. It uses the effect of an small low voltage electric current and a suitable electrolyte (solution).
What advantages does the method have?
The advantages this method has over the old standbys, like vinegar, Coke, muriatic acid, Naval Jelly, wire brushing, sand blasting etc. is that these methods all remove material to remove the rust, including un-rusted surfaces. With many, the metal is left with a "pickled" look or a characteristic colour and texture. The electrolytic method removes nothing: by returning surface rust to metallic iron, rust scale is loosened and can be easily removed. Un-rusted metal is not affected in any way.
What about screws, pivots, etc that are "rusted tight"?
The method will frequently solve these problems, without the need for force, which can break things.
Is it safe?
The solutions used are not hazardous; the voltages and currents are low, so there is no electrical hazard. No noxious fumes are produced. The method is self limiting: it is impossible to overclean an object.
Where did this method come from?
Electrolysis is a standard technique in the artefact restoration business. I wrote this up for the Chronicle of the Early American Industries Association a few years back. Most of the tool collectors around here use it:
What do I need?
A plastic tub; a stainless steel or iron electrode, water and washing soda (Some people have had success with baking soda) and a battery charger. About a tablespoon of soda to a gallon of water. If you have trouble locating the washing soda, household lye will work just fine. It's a tad more nasty, always wear eye protection and be sure to add the lye to the water (NOT water to lye!!!) The solution is weak, and is not harmful, though you might want to wear gloves.
How long does the solution last?
Forever, though the loosened rust will make it pretty disgusting after a while. Evaporation and electrolysis will deplete the water from the solution. Add water ONLY to bring the level back.
What about the iron electrode?
The iron electrode works best if it surrounds the object to be cleaned, since the cleaning is "line of sight" to a certain extent. The iron electrode will be eaten away with time. Stainless steel has the advantage (some alloys, but not all) that it is not eaten away.
How do I connect the battery charger?
THE POLARITY IS CRUCIAL!! The iron or stainless electrode is connected to the positive (red) terminal. The object being cleaned, to the negative(black). Submerge the object, making sure you have good contact, which can be difficult with heavily rusted objects.
How do I know if it is working?
Turn on the power. If your charger has a meter, be sure come current is flowing. Again, good electrical contact may be hard to make-it is essential. Fine bubbles will rise from the object.
How long do I leave it?
The time depends on the size of the object and of the iron electrode, and on the amount of rust. You will have to test the object by trying to wipe off the rust. If it is not completely clean, try again. Typical cleaning time for moderately rusted objects is a few hours. With heavily rusted objects can be left over night.
How do I get the rust off after I remove the object?
Rub the object under running water. A paper towel will help. For heavily rusted objects, a plastic pot scrubber can be used, carefully. Depending on the amount of original rust, you may have to re-treat.
My object is too big to fit. Can I clean part of it?
Yes. You can clean one end and then the other. Lap marks should be minimal if the cleaning was thorough.
After I take it out, then what?
The clean object will acquire surface rust very quickly, so wipe it dry and dry further in a warm oven or with a hair dryer. You may want to apply a light oil or a coat of wax to prevent further rusting.
Will the method remove pitting?
No. It only operates on the rust in immediate contact with unrusted metal. What's gone is gone.
What will it look like when I am done?
The surface of rusted metal is left black. Rusted pits are still pits. Shiny unrusted metal is untouched.
What about nickel plating, paint, japanning and the like?
Sound plating will not be affected. Plating under which rust has penetrated will usually be lifted. The solution may soften some paints. Test with a drop of solution in an inconspicuous place. Remove wood handles if possible before treating.
How can I handle objects that are awkward to clean?
There are lots of variants: suspending an electrode inside to clean a cavity in an object; using a sponge soaked in the electrolyte with a backing electrode to clean spots on large objects or things that shouldn't be submerged (like with lots of wood)
How can I dispose of the solution?
The bath will last until it gets so disgusting that you decide it is time for a fresh one. There is nothing especially nasty about it-it's mildly basic-so disposal is not a concern, except you may not want all the crud in your drains.
Can I use metal containers?
This is highly risky. Galvanised metal can introduce zinc into the solution. If you have used lye, it will attack aluminium. You may have problems with electrical shorts, etc. Stick to plastic.
How can I clean odd shaped objects?
Be ingenious. Plastic PVC pipe and eave troughs (gutters in the UK), wooden boxes with poly vapor barrier.
Ted Kinsey
