Calling Out The Internet BS

[IffykidMn]

Yep, it's just surface coloration. Even color case hardening on firearms, which is a much more involved process that penetrates somewhat deeper, is pretty fragile (as far as retaining the desirable color, anyway).

Interesting I always thought of color case hardening as decorative in nature as relatively low heat surface and not structural annealing temperatures.

 

[heimannm]

The temper colors (yellow, straw, brown, purple, blue) are oxidation and as such polish off very easily as Philbert has pointed out already.

Below 390° F no discoloration, over 575° F and you start to get irradiance where the material is glowing. Oxidation colors will appear when the material cools again.



Bluing of steel as in gun finishes is a different process.

Gun bluing is a chemical conversion process that transforms red iron oxide (rust) into black iron oxide (magnetite) to create a protective, corrosion-resistant finish on steel, improving both durability and appearance. It creates a thin, blue-black layer without changing metal dimensions, typically through hot, cold, or rust-bluing methods.

Mark

 

[Woodtroll]

Interesting I always thought of color case hardening as decorative in nature as relatively low heat surface and not structural annealing temperatures.

The coloring is certainly attractive, and now is done mainly as decoration, but casehardening was originally used to harden the outer layer of ferrous metal by driving more carbon into it under high heat while leaving a softer inner core, desirable for "toughness" in tools, guns, etc. made back before tool steels and such were developed. The item is packed in a container with charcoal and bone (in the case of firearms), the whole thing is heated to something like 1300 degrees, then quickly quenched, usually in oil. True color-casehardening is a pretty involved process. Here's a couple of links if you care to know more. Turnbull is considered an artist for his color case-hardening and gun restoration skills:

Color Case Hardening and Heat Treating - Upland Gun Company

A closer look at the function and fashion of various heat treatments, carburizing and color case hardening methods.

uplandguncompany.com

The History of Color Case Hardening and its Use on Vintage Firearms - Turnbull Restoration

Turnbull Restoration has played a pivotal role in preserving and perfecting this traditional metal finish and others over the last 40 years.

www.turnbullrestoration.com

As @heimannm pointed out, gun bluing or browning is a completely different process, whose purpose is to provide a protective layer on the steel. A good bluing job is certainly attractive, but the appearance was not the primary purpose originally.

Probably more than you wanted to know (sorry), but well-made tools like guns and chainsaws have always fascinated me, and some of my interest lies in all the many side details.

 

[Philbert]

he temper colors (yellow, straw, brown, purple, blue) are oxidation and as such polish off very easily as Philbert has pointed out already.

You have a specific, bar polishing tool, as I recall?

Philbert