This writeup is not intended to provide detailed instructions
on how to perform Color-Case hardening, but to explain what is
involved in the process.
Color-Case hardening involves the transfer of carbon atoms into
the surface of mild steel, to a depth of about 20-30 microns
(millionths of an inch), thru the process of heating
the parts and carbon to a specific temperature,
and maintaining the desired temperature for a desired time.
The hot parts, as well as the charcoal they're packed in, are then
dumped into a water quench. It is the quenching process, as well
as the types of charcoal used, which
"brings out" the beautiful colors so desirable in older firearms.
The process is simple from a technical viewpoint,
but it is highly artistic. Achieving colors and patterns which
very closely duplicate the results of the original manufacturer
are paramount. For example, while Colt color-case and Winchester
color-case are very similar, there are some differences between the two.
And there are both similarities and differences in the color-case of Sharps,
Spencer, Ballard and all other manufacturers of the time.
Mainly, the differences lie in the amounts and intensities of reds and
greens (if any). The blues, golds and grey's are fairly standard to
virtually all manufacturers. These colors are obtained by the types of
organic charcoals used, their ratio's in the mix, the amount and duration
of heat applied, and the quenching techniques used.
The type of mild steels used in the original parts also have a direct
bearing on the final results. Earlier Single Action frames, for example,
seem to take a slightly darker gold background, while the later vintages
take on more of a grey background.
There is virtually no control over the patterns produced, as they are governed
by such random events as the amounts of a particular type of
charcoal that contact the part during heating and the contact of
water during the quench.
Thin parts, such as '73 Winchester sideplates, as well as any other part which
may have thin spots within it, must be "blocked" (fig 7) to prevent
warpage which can occur when the hot part is quenched suddenly in cold water.
This blocking or bracing is done in a variety of ways. The blocks and braces must
be made specifically for each different part encountered in the
shop. Once made, they're used the next time that particular part comes
in for color case.
