Quote:
Originally Posted by DonVoigt
Straw has nothing to do with nitre bluing.
It is the color reached when steel is heated to around 430 degrees F.
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Done is entirely correct.
Straw (and fire blue) is not a finish; it's a byproduct of the flame hardening of low carbon steel to change the crystal structure of that low carbon steel to improve its resistance to abrasive wear. Flame hardening, regardless of whether that hardening is actually done by open flame, closed oven, immersion in molten metal, or some similar technique, produces a part that is hardened through and through. The surface color is determined by the heat to which the part is raised. That color will quickly oxidize to a muddy brown unless intentionally preserved.
Only small parts are flame hardened. On a Luger, these small parts include the safety, locking block, trigger, ejector (which usually has the color buffed off), and the hold open (deferentially hardened to fire blue). Flame hardened parts on a Mauser C96 included the trigger, safety, bolt stop, extractor, and rear sight lock bar.
The reason straw color disappeared from Lugers in the late 1930 is the same reason rust blue disappeared at the same point in time; at that time Mauser discovered a better way to heat treat small parts than flame hardening, and a better way to do surface carbonization than case hardening. For a detailed account of this new process and the ways in which it was a manufacturing improvement see Richard Law's "Backbone of the Wehrmacht (The German K98k Rifle 1934 – 1945)".