Rust is the eternal enemy of tools. Some have a degree of protection, whether that is the inclusion of Chromium as an alloy, being made from Aluminium (and thus having an Aluminium Oxide layer), or another coating added (paint, plastic, etc), but many others do not, and rust is soon to follow.
I’ve been looking for a way to easily reverse the chemical process, and have been giving Oxalic Acid a try. Readily available as a timber cleaning product, it is often used to remove the dead (grey) cells from a piece of timber to reveal its normal colouring.
I’ve started with a couple of rusted posts, and have graduated to a whole collection from the Torque Workcentre.
The liquid forms a great deal of tiny bubbles in the vicinity, so it is obviously doing something. I left a couple of test pieces for days, and it seemed to work, so graduated to the remaining collection (seen above). After a couple of days, I came back to it for a view.
Think the acid is basically exhausted, so after a look at the progress, I have emptied out the first bath, and refilled.
You can see the progress easily enough. But as I’m not sure, I’ve refreshed the bath for an additional go.
The earlier parts seems to be better (and they were in twice as long), so worth pursuing.
An interesting (ongoing) experiement. Got any other suggestions, pitch them in. There is an interesting situation where there is a skin forming in the liquid.
If anyone knows the mechanism (chemistry) here, let me know.
If they come out cleaner than that after another few days, will post an update photo. Any better rust removers that you know of (and I already know about the elbow grease one!)?
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Stu's Shed 
Evaporust (http://www.evapo-rust.com.au/) works from my experience – I’ve used it on a bunch of hand planes. Put parts in container, pour liquid on, wait overnight, pull out/rinse scrub lightly with scotchbrite pad. Its reusable, although more expensive than the Diggers formula you’ve used.
Electrolysis is usually highly recommended (haven’t gone that way myself). Vinegar is often mentioned.
Hi Stu,
It’s probably a polymerisation reaction between the oxalic acid and some other ingredient in the mix. Oxalic acid can be used as a polymerisation initiator. I’ve seen these skins form often in various situations, rather than the precipitate forming (like it is at the bottom of your solution) the precipitate forms as the solution evaporates and forms the skin. Much like soup does.
Cheers
Martin
It is an interesting thing – good way to remove the byproducts of a reaction! In this case as you’ve observed, the skin forms under the liquid, at the contact point between the metal bowl and the acid. It may be the result of a reaction there, rather than with the rust.
A coating of yellow ?product? remains on the outside of the items, that seems to need abrasives to remove (which still begs the question that if I have to use abrasives anyway, that would also remove the original rust!) Any idea what it would be, and whether another chemical can be used to remove that (such as a weak hydrochloric acid), that can then be washed away?
It’s most likely Iron (II) Oxalate: http://en.wikipedia.org/wiki/Iron(II)_oxalate
It coats the metal for obvious reasons as this is the source of Fe. It also appear in the bowl probably because there is some Fe metal (or rust) dissolved by the oxalic acid.
I’d avoid using any acid, especially HCl to remove the coating, as this will lead to further rusting.
I’m not sure if there are problems with this for woodworking tools, but I’ve had suggested to me to use whatever method of rust removal and then rub with some fish oil which creates a protective barrier.
Hi Stu. This too is unsolicited.
I unpacked a Robert Sorby pro plus early this arvo Mate and I had no problems with it and went on to have a fabulous arvo on chisels, some old ones which needed some various forms of ‘resurection” … prior to using the 120 grit belt.
We put on (very easily) a 240 grit belt and repeated same /similar over about 15 chisels. Easy and nice and enjoyable without frustration. I watered stoned the burr off and mate stropped them.
My stropping belt is an old barber’s horse hide number. Ideas on that too please.
An expensive item but I think it will help me with my lathe tools/ gouges and then be more interested in turning.