The "chemical" I was using comes from Birchwood Casey. They have several varieties for coloring different metals. It works pretty good although the surface have to be squeaky clean for best results.
I checked the web site and they have a "new" process (imagine that!!)more involved that what I had done in the past. Here is the link. Certainly doable by anybody if the quantity you have to purchase are not outrageous.
http://www.birchwoodcasey.com/news/5821.html
OK more info. I thought I had a one step process and I found it here;
http://www.birchwoodcasey.com/antiquing/options.html Scroll down to the bottom of the page, it's the ALUMA BLACK® A15 IMMERSION. I have a quart but the smallest now is 1 gallon @ $128. It you had a few guys that wanted to do this it would be very affordable.
Ken