This is peripherally on-topic, I figure. I inherited some tooling from my Dad (taps, dies, etc), and they had been sitting for years/decades in his unheated garage in Arkansas. Mostly good quality stuff, too, which he was funny about - he would wear the same thrift-store shirt until it fell apart, but stuff like this, he never scrimped.
Of course, it had a lot of surface and flash rust. Following the lead of my favorite Youtube machinist ( Adam Booth, AKA "Abom",
https://www.youtube.com/user/Abom79 ) I got some evapo-rust rust dissolver and tried it. It works *great*, the rust dissolves into solution and comes out completely rust-free, and at least moderately resistant to flash rusting. If you have tools, tooling, etc, that has rust, this is definitely the first thing to try. It's water-soluble, you put the tools in a plastic tub, pour in enough Evapo-Rust to cover them, cover it, and walk away. It works slowly but you will see flash rust gone in a few hours, and the clear liquid gets progressively browner and smells like rust. Heavy rust might take a few with occasional agitation, but it seems to work just dandy, much better than Naval Jelly (phosphoric acid), etc and no wire brushes, sandpaper, Scotch-brite, etc. needed.
Here's an "after" picture - I didn't think to take a "before" picture, but it was pretty dull an had a pretty even coat of vaguely orange surface rust. Obviously, it was not pitted too much, but this was a pretty good result.
What is won't do is fix rusty engine bearings - once they are rusted, Evapo-rust will certainly remove the rust, but it does nothing about the pitting, it can't put metal back on and polish it. Any more than the most superficial rust on bearings ruins them.
It is also chemically benign enough to not harm anything I have tried putting in it, like plastic, aluminum, brass, or copper. I have taken an old steel radio chassis that had been corroded in the past with rat pee, removed the RF and IF coils, and just dropped it in the tub and left it for a few days. All the capacitors, resistors, wiring, and tube sockets were completely unharmed, I washed it clean with running water, soap, and a fingernail brush in the bathtub, and then masked/painted it. It dried out, and then refurbished it normally (replaced wax-dip capacitors, left the sockets, wiring, and most of the resistors, all of which seemed unharmed by the experience).
The liquid turns brown to varying degrees, opaque when there is a lot of rust. But you can keep using it over and over, until it stops working. About $25 for a gallon, so cheap, and a very superior solution to any other I have tried.
Brett