Heat Bluing

It never failed, there was always some danged screw or pin I forgot when I was doing metal finishing. This process has been used forever because it works well. The bluing that is achieved is reasonably durable and can be made to blend in unnoticed with most blues. As you know cold blues are unacceptable for our work.

Start by making yourself a jar of oil. Don't obsess over it. Fill it up halfway with linseed oil and the other half of the way with Hoppes number 9. Boiled or raw linseed? Doesn't matter, use whatever you have handy. Old formula Hoppe's or new formula? You worry too much, just use whatever you have handy.

Polish up your little screw or pin - hold it with pliers - heat it up, you want to get it to more than blue, close to black, even sometimes to a very dull cherry (ya got to experiment) then dunk it in the oil mix. 

You can blue a pin or screw in less then a minute, it will be durable, it is heat blue, and it will match close (unnoticed) to charcoal blue, hot blue and rust blue.