Wow - usually I just lurk and learn. Finally, a question on something I actually know about!!

There are a lot of resources & formulas on the web for applying a hot patina to bronze - or anything with copper. Some of these patinas work well with steel. Basically you can do a palette of pinks through red to dark brown, and another palette of white through grey to black. By combining these two you can get light browns and yellows.

Hot patinas are best applied from a spray bottle to steel that is about 400F. Oxy/Acetylene torches are way too hot and running straight acetylene does not work due to the soot. You have to use a propane torch -- the best size are the big ones which are used to burn weeds or thaw pipes. The easiest method is heat with one hand and spray with the other.

One source for chemicals formulas is
http://www.bryantlaboratory.com/patina.html

You only need two formulas. The red-brown is ferric nitrate and the white-black is bismuth nitrate, stannic oxide, and titanium dioxide. Some formulas are on the Bryant lab site, others are on bronze patina sites such as http://www.whiteriverfoundry.com/bronze_patina_basics.htm

You can't do blues, greens, or silver with steel unless you use dye. I've never tried it but I've seen some beautiful work. I think Bryant Labs and some sculpture web sites sell dyes.

Wear nitrile gloves, a good chemical mask, and do it outside or with good ventilation. The fumes are not poisons but they aren't healthy either.

Let me know if you need more info.