Hi Shane,
Just put the plate, flintcock, and top jaw in the oven. You don't want to mess with the temper on any of the other parts. Shane, let me describe a few details on heat treating steel specific to locks that will help you understand the different processes. Steel is iron combined with carbon. The more carbon, the harder the steel can be made. Hardening is done by heating the steel to bright red or orange color and then quenching it immediately in some solution that could be water, brine (water and salt), or light oil (transmission oil, quenching oil, canola oil). The rapid cooling in a sense, polymerizes the steel into a hard material. That hard material is required to produce sparks and resist wear on moving parts that are also under stress like tumblers and sears, and to make springs. However, after hardening,the steel is brittle like glass. It must be tempered, which draws out some of that brittleness, to be useful for lock parts. Tempering happens when you heat the hardened steel to a temperature that does not soften it (well below the hardening temperature) but draws off some of the brittleness. The use of the part determines the tempering temperature. For a frizzen, you want it hard but not too hard so that a flint can cut it to produce sparks (sparks are shards of steel cut from the frizzen and heated to incendiary by the flint.) But you don't want the frizzen so hard that the shock of the flint hitting it breaks it like glass. So you temper the hardened frizzen to 375-400 degrees F. The internal parts undergo stresses and don't need to be as hard as the frizzen so they are tempered to blue (600 degrees F). Note, the higher the tempering temperature, the more hardness is softened and the less brittle and more tensile strength the part has. For example, a steel part tempered to 375 will cut into a steel part tempered at 600 degrees. A spring must be tempered to 650-750 degrees to prevent breakage. During the 18th century, steel was a very precious material. It could not be made in large quantity cheaply and was as valuable as silver. Not until the Bessemer process was invented during the 19th century was steel a cheap commodity. As a result, in times before the mid 19th century, locks were mostly made from wrought iron containing little or no carbon. They could never be hardened and made into working locks. The solution was to add carbon from charcoal or burnt leather in the case hardening process to the surface of the iron part, converting it to a skin or "case" of carbon steel that could be hardened. Today's lock parts are steel containing enough carbon to be hardened simply by heating to bright red and quenching. The commercial lock makers then temper the parts to their appropriate levels. In the case of your lock, my advice will allow you to color it with a bronze color but not affect the hardening and tempering of the parts done by the manufacturer. My advice is simply cosmetic and historically correct.
dave
