Standard chemical processes may be a better and more consistent way to blue small parts, but require a greater expenditure than does simple firebluing with a basic heat source. Using a propane/butane torch works for firebluing, but it is a delicate matter to reach the correct temperature without heating the parts too quickly and ending up with lighter blues and grays. If you heat past the correct color in this way, your only choice is to begin the process again.
A more controlled firebluing process that I now use is as follows: I polish the parts to the desired degree of luster, chemically clean them, then use fine steel wire to make hangers for the parts. I heat my kitchen oven to 570 degrees Fahrenheit (the correct temperature for deep blue, and one that my moderately old oven will reach), and I simply place an industrial thermometer on the rack and preheat the oven until I get the correct temperature. I hang the parts on the rack where the thermometer resides, close the door and watch until the parts move through the color range to deep blue. When the correct color is achieved, I simply remove the parts and let them air cool. I'm aware that some folks immediately quench the parts in oil or water, but I seem to get a good result without quenching. The color achieved lasts well, and can easily be redone if the bluing becomes worn over time. A good steel color chart that will guide your efforts can be seen at:
http://www.smex.net.au/Reference/SteelColours.htm
