Does anyone know a chemical or formula for putting a brass or copper patina on steel. I know about brass brushing at a black heat but for this job it would be impractical.

I remember somebody either leaving a copper/brass rod in vinegar, or another acid, or reusing the same acid that had been used on some copper/brass, and getting a patina like that on a knife.

blacksmith supply sells all sorts of patinas for metalworking

I believe cupric or copper sulphate will plate iron or steel with copper. The other option I know of is electroplating.

Of course you could look in the yellow pages for a plating business and ask for a quote.

Frosty

Alan. This is something I have experamented with quite a bit, so I can probably answer your question. But it would help to know what you are trying to plate, and what kind of patina you want to achive, also what kind of budget and time to play around you have?

If you want to do it yourself, Frosty is right. copper sulfate is the chemical you want. The stuff I use is Roebic K77 root killer. 99.8% copper sulfate. It costs about $10.00 at Ace.
You can either disolve it in hot water, and then use it as is for an electoplating solution. Or add a little bit of acid to it ( I use sulfuric acid, sold as a drain opener) and use it as a cold plating solution that you just wipe onto clean steel and it leaves a copper coating.
The down side is that electroplating is kind of an art, and you will need to experament quite a bit to get a nice coating thats thick enough, and sticks good.
The cold plating solution, is fairly foolproof, but doesn't really leave a thick enough layer of copper to do a decent patina.

You can also buy premade cold plating copper solution through most of the regular supply places. But it's a bit pricy at $100.00 a gallon last time i bought some, also hazmat shipping etc.
There is a place in CA. called (Sur Fin) that sells an antique bronze cold plating solution for about the same price. Which doesn't look to bad, kind of looks like dull dirty bronze more than an even patina. But depending on the application can look pretty nice.
You might also check out some of the sculpt neuveo (sp?) patinas if you are looking to get the verdigris green patina look on steel. They are not a true patina, but more like a paint.

I'm guessing that heating the whole piece is the problem w/ the hot brass brush technique? If so there is a way around that. If you go to a decent welding supply place, they can order you a bronze brush to go on your grinder, (angle or bench). Then you just go over the whole piece cold and the heat generated from friction will wipe the bronze onto the piece. But the bronze brushes aren't cheap.(don't try to use the brass coated steel brushes they won't work.)