Question on Heat Treating on Hammers and Triggers

[epidoc]

I was just watching a YouTube video from Midway on fire bluing small gun parts with potassium nitrate, and got to wondering. How does Smith and Wesson heat treat their hammers and triggers to produce that remarkable coloration? My earliest S&W is a Triple Lock that dates to 1911, and my newest is a pre-Model 29 that dates to 1957, and both have same distinctive coloring on the hammer and trigger.

 

[Pontiaker]

Its called case hardening. It only hardens the outer layer of the steel. I dont remember all the steps but you cook the part wrapped and sealed in heat treat foil in bone charcoal. There are lots of ways to do this, everyone has their little secret and what exactly they use. If you need a part redone and want that awesome looking finish look up Doug Turnbull. He does some of the best case hardening in the world.

 

[2152hq]

Bluing (fire bluing) with molten potasium nitrate will only give you the color,,not a hardened surface. Also called 'Nitre Bluing'.

It's actually an annealing process. It can and is used to draw springs to the correct temper (spring temper 'blue' color). The salt melts initially at around 500F but can be used up to around 850F for different applications and colors.
Quick and fairly easy to use. Dangerous because of the high temps of course. A spot of it on you will burn straight thru your cloths and into your skin before you have a chance to even now you've been hit by them. I know from experience!

Color case hardening is an entirely different process. A bone and wood charcoal pack with the part brought to approx 1450F and then quenched in water (sometimes oil,,but that will yeild little color). Lot's of small technique tweeks in the process but that's the simplified version of what's done.
S&W parts are bone and charcoal color cased.

Color case hardening is also done with molten cyanide (potasium cyanide,,a salt that is heated and melted as in the fire blue method) and the part is held in the molten salt and then quickly quenched in water.
Cyanide color gives a different pattern/look than bonecharcoal color hardening. The extreme dangers involved in the handling of the cyanide compound are well known.

It's still used in controlled industrial situations and a couple restoration shops adv. they do it. I don't know if they send the work out or not to be done.
I did work for a small gunshop in the 70's that used to put a tiny amt of potassium cyanide into the hot bluing salts so they could reblue SxS barrels w/o damaging the solder. Said to work,,but it took it's toll on the barn cat population that would stroll through that area and pick up the stuff in the precipitated dust on the floor, tables, etc. Unforgiving stuff. I always stayed clear of the bluing room when there!

Heintzlemann's in NJ still does gun work in cyanide for the trade. They are an industrial heat treat co & started back in 1917 or so.
They did the AH Fox guns when they changed from bone/charcoal to the cyanide process just after WW1 till they were bought out by Savage..