Another evaporust user -- I've cleaned about 1,500 tools since last summer that way, plus a few by electrolysis, which produces similar results but is better on large items and useless for (say) a box of 200 drill bits. I buy Evaporust in 5 gallon buckets from Northern Tool, especially when I can find it on sale in the "hot deals" (or whatever they call it) newsletter, which gives me free shipping. TSC sells it by the gallon, which costs a bit more. E-R works better on some irons and steels than others (I find it worst on the plated ones); works better in warm weather than cold; removes some finishes, especially oxide finishes and japanning; gets used up in that as you use it, it quickly reaches a point where it turns black and leaves as much rust on a tool as it takes off; and even at its best leaves a light matte surface (usu grey) that needs to be buffed off with a soft wire wheel (I use one with brass-covered steel bristles at low rpms). Iron that is blistered with rust does not respond too well, and of course deeply pitted iron or steel remains deeply pitted. I find that electrolysis and Evaporust (which works by chelation, just like the old molasses-and-lemon-juice method) are quite similar in results: both leave a matte surface, both usually take 3 or 4 hours, but may need to be left in longer if seriously rusted.
For electrolysis I use a manual battery charger set at 6v/2amp for the power, a 30-gallon plastic trash can full of rainwater for the water supply, Arm&Hammer washing soda for the electrolyte, and a coil of common concrete-reinforcing mesh standing in the water as the cathode (with a bit of copper strip attached to make a convenient spot to attach the clip).
On this page:
http://www-personal.umich.edu/~pfs/fun/Kiwanis/refurb.html you'll find a log of the tools I've cleaned for the local thrift sale; links in the 'date borrowed' and 'date returned' columns will usually show before-and-after pix after my rather hasty de-rusting and occasional repainting and sharpening. Most of these are not intended as collectables, but as straight user tools, so I'm not too worried about authenticity and patina.
And here is the review I left on the NorthernTools site, regarding Evaporust:
" I've used two [make that 20 gallons now] gallons over the past three weeks to de-rust about 150 [now 1500] hand tools (donated to a charity thrift store) which were suffering from everything from light surface rust to deep pitting; some of the tools had the distinctive look of metal that had lived the last thirty years on, or under, a barn floor. Generally successful, sometimes surprisingly so, though sometimes need to soak them for up to 24 hours in extreme cases. Does better in warm weather, I think. Wears out when completely black, maybe 30-50 tools per gallon. Tends to leave a matte gray or black surface finish behind that needs to be removed with a wire wheel, wire brush, or steel wool, especially after the first use. Works best on mild steel or cast or malleable/ductile iron; much less successful on hardened steel (e.g. files) or alloy/tool steels (this is explicit in the instructions). Will soften and often remove paint. Will completely remove some japanning-like coatings and black oxide finishes. If the tool has wooden parts, will of course soak into the wood and may stain it black; remove them first if you can. In the attached photo (my latest batch of refurbishings), the large coarse rasp (top left) resisted most stubbornly -- took two days--; most of the rest did well. The Utica wrench (third wrench up) still shows staining in the plated alloy steel. Many of these started as almost unrecognizable blobs of rust., e.g. the old Stanley try square, the long-handled float lying behind it, and the tack puller to its left. In short, this is very good stuff, it won't last quite as long as you'd like, and it won't work quite as well as you hope on everything. But invaluable. Having used up my first two gallons, I'm prepared to buy the 5-gal. bucket and go from there. "