Lynton McKenzie used to say something to the effect that, getting the correct hardness is no trick and neither is getting nice colors. Getting both without damage or warpage is difficult.
I've always said that heating any steel part red hot and dumping in a bucket of water is simply foolish~~
When I taught at the Summer gunsmithing classes at Trinidad State years ago I witnessed a case coloring session when a glowing red-hot Ruger #1 action was dumped in the quench tank. I cringed~~Six months later a visitor to my shop proudly showed me that same action. I cringed again~~ IMO 4140 steel (40 points of carbon) should not be subjected to that treatment. I know it is being done at lower temperature, but I would never do it.
The Hagn action shown above was specifically made from 8620 (20 points of carbon) so it could be properly heat treated by case hardening. This hardening is to provide a slick skin, increases wear and corrosion resistance. The beautiful colors are a bi-product.
Bertuzzi sidelock from my shop. Lovely case colors (Turnbull) hiding a couple thousand dollars of Mike Dubber engraving.
