Sure. There's two I know of. There's Birchwood-Casey Presto Black, an acidic solution containing copper and selenium, that colors steel black at room temperature. The only requirement is that the metal be absolutely clean.
The other is Jet-Kote 54, a product my company used to make when we were based in California. Its chemistry is similar, but it's not a reverse engineered knockoff, it's something I invented. I'm trying to get a production facility going here in New York, but that may take a bit more time.
There are public domain formulas (I started with one) but the one I used was powdery and rubbed off easily - it needed to be jazzed up with some other chemistry before it worked well enough to satisfy me.
Do be advised, though: these cold blacks are purely cosmetic. They confer no corrosion resistance at all. And, though they will stand up to some mild rubbing, serious abrasion, like "scratching" will take them right off. You'd need to top off with some kind of lacquer or something.
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