I received a private request for more complete details on this method I described in a recent post, so thought I would just put it up for all. This is copied directly from an Ithaca Service manual of about 25yrs ago.

To Repair or Restore Color Case on Perazzi's
1; This is a serious problem on guns that have been used extensively.
Equipment Required:
a. Cold blue (we use 44-40)
b. “Q” tips (cotton swabs on a stick)
c. Torch or other heat source
d. Paint remover (we use “Kwick”)
e. Fine steel wool
2; Procedure:
(1) Remove everything from the receiver.
(2) Remove lacquer from the receiver using “Kwick” or other liquid paint remover
(3) Wash receiver in a good solvent or boil with detergent.
(4) Using your heat source, heat the receiver to
a point where liquid cold blue will dry almost
instantly, (about 160°F)
(5) Using a “Q” tip, draw squiggly lines or
whatever is necessary to match existing color
hardening.
Note* If you have polished the receiver to bare
metal, space your lines about ¼” apart on the
first pass, then fill in on a 2nd pass.
(6) Using fine steel wool dipped in oil, remove
the oxidation from the receiver. Be careful
not to remove the color.
(7) Wash in good solvent. Do not touch before
applying lacquer.
(8) Spray with acrylic plastic from “Koloid”
(9) Reassemble gun & return to a satisfied
customer.
Note** This procedure does not affect the case
hardening. It only restores the color.

A few things of note; I also tried Brownell's Oxpho blue & found it worked same as 44-40. I do not recall the brand of Acrylic I used but don't recall Koloid being available where I purchased mine. Also note that though a "Torch" is listed as a heat source, it is used to heat the part to an overall temp of only about 160°F, not enough to bring about any change of color, not even the faintest straw or yellow, much less blue. No concentration of heat is applied to bring about a color change in the metal (A simple propane torch is suffecient heat for the job). Outside of a genuine bone/charcoal case-hardening by knowledgable professional, this is the only procedure I am currently aware of to produce a semblance of case colors with no damage to existing heat-treatment.
Miller
PS; this is applicable to guns other than Perazzi's and can be simply polished off should you decide to go with another finish later.


Miller/TN
I Didn't Say Everything I Said, Yogi Berra