I use a two-burner Coleman stove connected to a 20 lb. propane tank. More than enough heat and lasts a long time. The tank that I use is one that I made out of 20 gauge steel. I had a problem with uneven heating because of the thinness of the steel and consequent uneven colour in the piece being blued. I solved the problem by putting a sheet of 3/16" steel plate under the tank to diffuse the heat. I should point out that I use the old Herter's Belgian Blue (an "express" rust blue), and it does a lovely job, ending up looking like the old Superposed guns..
