Q's Re: Charcoal bluing...

[Collector]

I'm looking, here, for answers of a historical and technical nature.  Any help would be appreciated.

Q-1.)  How far back, in history, does this metal treatment/finish go? 

Medieval Europe, or is it recognized as a significantly more modern technique?

Q-2.)  If the steel object is already heat-treated, is this an impediment to the charcoal bluing process?

Q-3.)  If the steel object requires heat-treatment, can this be performed after the charcoal bluing process is completed?

Q-4.)  At what recommended temperature, or temperature range (in F degrees) is this treatment best accomplished? 

Are best results obtained by
a.) bringing the steel part up to a certain/specific process temperature
and thereafter maintaining this temperature for 'X' hours?

-or-

b.) steel is at ambient temperature, inserted into a charcoal bed that has reached 'X' degrees F and thereafter left as bed temperature gradually dissipates.

c.) is there an optimal time limit that steel is left in the bed and then removed to cool in an ambient environment (without extremes, of course)?

Q-5.)  If the charcoal blued steel is to have other materials inlayed (e.g. bronze) into it, at what point is the steel surface prepared for the inlay?

Q-6.)  If the metal inlay work is performed after surface is charcoal blued, how is the blued surface protected from damage?

As always, my thanks...

[WadePatton]

I've only done small pieces but loved their color and durability, so I can answer a thing or two.

One thing-there's no "inserting/removing" or you risk oxidation (red not blue).  You want your steel in an oxygen-poor environment for the duration of heating and cooling.  I packed mine in tins and threw it in the fire, removed after the fire was gone.  Used the woodstove.

Have plans to do a bbl or two in a pit fire.  Pack bbl into pipe.  Burn fire in trench, making bed of coals, then insert packed bbl into trench, cover with coals.  Remove when cool.

Some random thoughts on  your other points.  Heat treating is one of three things: annealing, hardening, case hardening, tempering. Wait, what? That's FOUR things. Well not really when you realize that tempering is simply a "limited annealing".

The carbon content of the metal has most to do with which processes are necessary.  The most critical for temperature control is tempering, but has been done by color for a few hunnert years.

IIRC, charcoal bluing temps are perfectly safe for bbls of the materials commonly used.  Possibly even "stress relieving".

Where's JK?    

[jerrywh]

 collector.
   I don't mind answering some of your questions but I would like to know who you are. You can send me a personal message if you want.

[jerrywh]

 Collector.
  Iron and steel bluing goes back to the beginning of the Iron Age. Any blacksmith has noticed the change of colors as the temp. of the iron goes through the color ranges.  A good friend of mine is Robert Evans.  Robert Evans is one of the founding members of the Firearms Engravers of America and he has a master’s degree in history. He is also a sword collector. Robert says that Bluing was first done on a commercial basis by the sword makers in Europe.  At that time the swords were blued in a large pile of hot sand. They kept the sand pile on an iron plate on top of a huge forge.  The swords were just stuck in the sand and withdrawn at times to check the color until the desired color was reached.
  Some of this is speculation because the arts were very secretive back then and most of them were done within a guild.
   Soon some of the gun makers began to have parts done the same way. We can find gun barrels on fancy European guns with blued barrels in the 18th century and probably back into the wheel lock days.
   I can't say that Viking swords were ever blued for sure though. That requires a lot of research.  The process was usually done on presentation type arms but also by request of the clients.
Q-2.)  If the steel object is already heat-treated, is this an impediment to the charcoal bluing process?
            It depends on the temper of the original object. A sword would probably be tempered to about the same temp. as is required to blue one so the bluing probably wouldn't make any difference and may improve it. According to Smith and Wesson any temp. under 800° will not affect a 44mag revolver so it will not affect a muzzle loader. Temper blue or charcoal does not require a temp over 650°f the time depends on the mass of the object being blued.
Q-3.)  If the steel object requires heat-treatment, can this be performed after the charcoal bluing process is completed?
    The answer is no. Not without destroying the blue.  If the temp. is increased to 700° or more the blue color will turn to gray and it will not return at any higher temp.  If the steel is raised to a temp of about 1300° or more it will begin to show a heavy blue gray oxide. If maintained at that temp for long it will begin to flake off like chipped enamel.
Q-4.)  At what recommended temperature or temperature range (in F degrees) is this treatment best accomplished?
    The blue begins to appear about 560°f as a purple blue then a dark blue at about 600° then continues to get lighter until it fades into gray at about 675° to 700°
     More later.