Commenting on the original question of this post:

In the early 1970s a gentleman from across the pond named Brian Ebbs brought over a nice selection of British double rifles that were each totally restored to as new condition. Most were Alexander Henrys in .450 or .500 caliber. They were priced at $500.00 each. I was just out of college and didn't have the money to buy them then. Anyway, the point is that the color hardening on them was very similar to the work that Doug Turnbull
does. I believe that Brian's rifles were color hardened by St. Ledger. I would like to see a picture of one of those rifles if any member of this discussion group owns one. They were magnificent.