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I am wondering if anyone here can describe how straw "blueing" was done on Luger parts and how fire blueing was done on Colt screws?
Jim

I'm not a Luger expert, but colors from light straw to deep purple are possible/indicative of the heat applied to steels. These temperatures are in the range where 'tempering' or 'drawing' (softening) takes place on fully hardened steel. So, the process was heat a steel of sufficient carbon content to above the critical temp (typically 1425F) and quench it. This is now a fully hardened steel. The hardness will depend on the carbon content as well as some other alloying agents. Then the steel is polished and then heated slowly to the tempering temperature. In the days before temperature monitored ovens, the surface color was the indicator.
http://www.anvilfire.com/index.php?bodyN...20anvilfire.com

Tool Steel Color vs Temperature
2000°F Bright yellow 1093°C
1900°F Dark yellow 1038°C
1800°F Orange yellow 982°C
1700°F Orange 927°C
1600°F Orange red 871°C
1500°F Bright red 816°C
1400°F Red 760°C
1300°F Medium red 704°C
1200°F Dull red 649°C
1100°F Slight red 593°C
1000°F Very slight red, mostly grey 538°C
0800°F Dark grey 427°C
0575°F Blue 302°C
0540°F Dark Purple 282°C
0520°F Purple 271°C
0500°F Brown/Purple 260°C
0480°F Brown 249°C
0465°F Dark Straw 241°C
0445°F Light Straw 229°C
0390°F Faint Straw 199°C
Steel exhibits different colors depending on temperature. Temperatures above 800°F (427°C) produce incandescent colors; the atoms in the steel are so energized by heat that they give off photons. Temperatures below 800°F (427°C) produce oxidation colors. As the steel is heated, an oxide layer forms on the surface; its thickness (and thus the interference color as light is reflected) is a function of temperature. These colors may be used in tempering tool steel.
I hope this will help
Casey

Thanks Chuck and Casey:
Will anyone take a stab at fire blueing?
Jim

oxidation caused by heat/fire. mc

Both the straw color of the Luger triggers and other parts as well as the brilliant blue color found on the Colt screws can easily be duplicated with nitre salts blueing. I use the salts from Brownells and have duplicated the colors you describe many times. They come with a temperature chart that varys from the one above, but functions the same way. You simply melt the salts in the appropriate vessel, I use the "1/4 tank" from Brownells, bring the melted salts to the right temperature using a blueing thermometer, immerse the polished parts and watch for the color change. A very simple process that works well for small parts.

Chief Shotguns:
If I'm reading your post above correctly you can do this "stove top" at home? I'm sure we all know that some of the temperatures listed above would be impossible to attain at home.
Jim

Yes, absolutely. I have not tried to attain the high temperatures on the above chart, but you can easily get the molten salts into the 700 degree plus range. That will do what you said you were looking for. I certainly would not attempt to blue larger parts, like a pistol frame or slide, on a stove top.

To be precise, I "cook" outside on a cast iron natural gas burner actually made for fish cooking, on my covered patio area. Before I started that, I did a few runs in the kitchen, but the "other" person who lives here with me prefers the outdoor method. No reason at all this could not be done in the kitchen, as I have done, with a bit of care.