My understanding was that in the 1800's, the vibrant colors imparted during case-hardening were simply a pleasant by-product of the techniques used at that time, not a specific goal. More modern and expedient techniques of case-hardening achieve the same hardening result, but without imparting the colors. Hence in modern literature, we have to specify "color case-hardening" versus "case-hardening", while in the original 19th century literature they don't make that distinction.
Glenn M. Kaye
73rd New York Volunteer Infantry
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