I wanted to give charcoal bluing a try, I found this recipe in Clyde Baker's book "Modern Gunsmithing"
It reads:
An old English gun maker gave me the following which I have seen him use to produce very fine work, although I have never used it myself:
Make a boxy of heavy sheet iron large enough to hold the largest part to be blued. It is not necessary to rivet or weld the box, merely fold the corners. Fill it with pulverized wood charcoal in lumps about the size of a small pea, and heat in a furnace or large forge until the charcoal is partly burning throughout, but not quite redhot. Attach an iron rod at least two feet long to the gun, and bury it in the glowing mass, allowing the rod to stick out for handling. In 5 to 10 minutes, lift out and examine it. If the color has started, take a large wad of clean cotton waste or tow, dip it into dry powdered lime and rub vigorously over every part and work fast. You may be fooled at the first bright blue that appears. This is merely a "tempering color" and must be disregarded. It will not wear, and it is not the blue you are after. Continue the treatment until a deep blue-black similar to that seen on Colt revolvers has developed. Let cool in the air (do not quench) then apply any good light gun oil.
