How do you do this?
And do you have to remove the black oxide finish first? If so, how did you do that?
There are several methods and kits for bluing. It can be done with cold methods using products such as Brownell's oxphoblue or Birchwood Casey's bluing kits. You can check out either Brownell's or MidwayUSA for bluing kits and products. Gunsmiths usually use a hot bluing technique using hot salts and tanks. Cold bluing is often used for small parts or touchups around items like ironsights etc. There is an older slow rust bluing technique which involves high humidity and salts. This is the type typically found on shotguns since barrel solder can't take the heat of hot nitre bluing.
But for a layman's way of performing hot nitre bluing (which is arguably the best method for tools anyways), check out this article by Marshall Stanton over at Beartoothbullets where he uses stump remover to blue some parts on a Marlin Trapper Carbine project. Pretty nifty and informative for a simple and inexpensive means of hot nitre bluing.
Note: If you don't want to read the entire article, skip down to where you see the stump remover pics and start reading there. Actually, in the previous part on plumb browning, he also details that you need to clean and degrease the parts too.
http://beartoothbullets.com/tech_notes/archive_tech_notes.htm/58
You can also do a search on youtube for bluing and see lots of videos on the subject.
For instance, here is a MidwayUSA video by Larry Potterfield, founder of MidwayUSA illustrating the nitre blueing technique.
