Grant Erwin writes:
So what's Evapo-Rust, and why would I want it?

Suspected to be a few cents worth of EDTA in water for $20/gallon. The
bottler won't be honest about what it is. The publish an MSDS that sez
nothing is in it that is hazardous. This in a world where water is
hazardous for MSDS purposes.
It's one of those things that 3M doesn't think is worth selling, but is
effectively hustled by a small outfit. Such as via newsgroup spam and
inflated "military" testimonials.
Really, what kind of technician relies on a product that has no scientific
basis, precisely because the maker won't tell you what's in it?
Sounds like someone needs to find some EDTA and run a test.

Ok, here's a testimonial:

I've been using Evaporust for 2 years, ever since the new sales manager
gave me a couple gallons to try. I've de-rusted taps & dies, machine
tooling of all types, antique lathes, gun parts, you name it.

The stuff is straw-colored, slightly thicker than water.
You place your nasty, rusted, even slightly oily part in a plastic
container, then pour enough Evaporust over it to cover it.
Go away for 2 hours or 2 months, maybe longer. When you pull it out, it
is shiny and clean, with maybe a black oxide coating on it that wipes
off. High-carbon tooling will retain a dark color.
It doesn't hurt most paints, and doesn't attack any metal that i have
found. I use aluminum round cut-offs to take up space, they still look new.
You can re-use it until it's so black you hate to touch it, then pour
it down the drain or on the lawn.
Right now I have some sort of antique formula car suspension piece
soaking. It was nickle-plated, badly rust-freckled. I couln't get it all
into the pan (a flower-planting trough from HD) so I turned it over last
rip out to the shop. The part that was soaked was clean as a pin. It
leaves a thin coat that will prevent flash-rust until you can get it
protected, but I usually just wipe it off and leave it.

I'm a believer. You guys can futz with acid and electrodes all you want,
but I've already cut out that coupon and I'll stop by HF and pick up a
couple gallons.
The irony is I can't get the people here where I work to buy the
stuff so we can sell it. I think AutoZone also sells it.