In the past I have done some Hot Salts Blacking, Express (Hot) rust blue & the traditional cold rust blue. While the cold rust process is stretched out over several days I found it to be the easiest & was my preferred method.

All the essential equipment needed is a container large enough to hold the barrels covered with water & enough heat to boil the water. You will of course have to card the formed rust after boiling. This is ideally done with a fine wire brush rotating at a relatively slow speed, but for limited use can be done with a hand brush or even steel wool.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra