Will try to reply with my limited English....
In a Mauser action, the bolt, receiver and parts are made from a low alloy, medium-carbon, steel.
The color case hardening is a surface carbon cementation and it makes the carburized surface very hard, leaving the core relatively soft.
The hardening that is not very deep (no more than 1/10° of millimeter) gives a great resistance to wear and smooths the action.
The core of the treated parts, though and resilient, becomes more resistant and can stand hard use.
In fact, colors are an "accident" and in the past, they were washed with a solution of chloride acid, letting a soft grey finish know as "French grey".
Even if the method used now is the same than in the past, the use of electronic controlled ovens narrows the error margin.
Notice however that the newly hardened parts must be varnished to retain their vivid colors.

DORLEAC
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