On Thu, 5 Jan 2006 06:21:57 +0000, Joepy
wrote:

A friend of mine that gunsmiths uses a recipe of 50/50 (IIRC) sodium
hydroxide (Lye) and ammonium nitrate in a boiling solution.

That's "melting", not "boiling". Melting this stuff is bad enough! You
don't need the caustic soda, but you have to choose between a higher
melting point, or a lower eutectic melting point and a mixture that's
now caustic as well as a powerful oxidiser. I can't over-emphasise what
a fire hazard this stuff is - splashes onto a wooden workbench are quite
capable of starting fires.

Yields a really durable black oxide finish.

Shame to go to all this trouble and just end up with black. This is one
of the few blueing processes where it's also easy to get good variegated
colour blueing effects.

For "art steelwork", then hot oil blueing is attractive too, but IMHO
we've all seen a bit too much of this stuff coming in as cheap import
tat for the last few years. I've stopped making it.

If you're doing any blueing, go read some really old gunsmithing books
first. This stuff isn't new, but there is quite a bit of skill and
experimenation to it.