The process essentially as described in Machinery's Handbook, with the exception of adjustment of the carbonaceous mat'l for color, is what is described in W W Greeners book "The Gun" & is also given by an L C Smith engineer in the "Plans & Specifications" book. Many of the processes involved in producing these old classic guns from rust bluing, oil finishing stocks etc were all time consuming. For about the last 50 years I have read at every turn that the price of labor (Brought about by the labor unions, of which I was a member) was what killed the double gun in America. It was of course many more aspects involved, not the least of which was the desire for "FirePower". That time consuming method of case-hardening though was indeed the method by which the old classic gun-frames with color were finished. Chemical finishing of an alloy steel simply for the purpose of producing clor is a late phenomenum.
Miller
