[TheForge] Re: A different needle question

[Mike Spencer]

Bruce wrote:

> A tempering operation (to purple or blue, probably) is quite easy on
> a chisel, but even SEEING the colors on a needle is a challenge.
> For one thing, there's no good surface to polish.
>
> I've tried a couple methods, all without success -- my toaster over
> doesn't get hot enough, like, maybe 450 F, despite what the dial
> says.  (520 F = purple, 540 F = blue, 590 F = peacock, according to
> one reference.)

Molten sodium nitrate (MP 306C  582.8F) or potassium nitrate (MP 334C
633.2F) or a mixture of them.

I recall reading a long time ago that some person or company used a
molten KNO3/NaNO3 mixture to create an ornamental blue patina [1] on fancy
dress spurs. [2] Temp seems about right for what you're doing.

With your background, I don't suppose I need to mention the potential
risk of dropping random organic material into molten nitrates. :-)


- Mike


[1] Not to be confused with "hot bluing" in a water solution of
    potassium nitrate and sodium hydroxide.

[2] Does anyone here wear spurs with formal wear?  1st Cav officers at
    the innaugural ball? Senior RCMP officers at a coronation? Or
    maybe just drugstore cowboys with hand-made $1000 boots?  Or kinky
    people who...um, not going there.


-- 
Michael Spencer                  Nova Scotia, Canada       .~. 
                                                           /V\ 
mspencer at tallships.ca                                     /( )\
http://home.tallships.ca/mspencer/                        ^^-^^