Unless the gun is to be heavily aged as in most of the iron mounted guns I do, I like to heat blue my triggers and lock screws. I throw them in the heat treat oven and run the temp to 560 F. The result is usually pretty good. However, these parts must be polished to a mirror finish and degreased for the best result. If you do this, the finish is pretty durable. A heat blue looks like $#*! and flakes off unless the surface is perfect. A cold blue would probably be easier, but it doesn't look the same. Heat blued triggers and lock screws can really make a nice carved and engraved rifle pop.