It doesn't like to darken or oxidize because of it's nickel content. No silver in it. Has copper & zinc though.
MOst cold gun blue will get you a yellow look to it and that's about all.
BirchWood CAsey SUPER gunblue will impart a black coating on nickelsilver (German Silver).
Not the B/C 'Perma Blue',,,but their 'Super Gun Blue'.
The PermaBlue won't do much to N/S,,just that yellowish color previously mentioned.
I've used it and it works well. Most everyone else says it works well.
A few comments on the almighty net say it doesn't work. Maybe a contaminated bottle of the stuff, uncleaned surfaces,,or perhaps B/C changed the chemicals in it.
Wouldn't be the first time they've done that to their products.
There's a product called JAX Blackener that is for use on steel and nickel.
Same idea,, a jet black coating.
https://jaxchemical.com/shop/jax-iron-steel-nickel-blackener/Supposed to work exc on N/S
None of these give you a very tough finish and they usually take some experimentation in application techniques and even sometimes diluting them to get the best results.
A thin overcoating of clear finish like that applied over case colors probably isnt a bad idea.
Another is Midas Nickel Oxidizer.
This one probably is NOT what you are looking for. This product is more for sculpture and engravings where you want to leave darkened patina in the crevices and cuts of the part or work. Plus some distress to the surface overall.
An instant antique finish would be a better description.
There was a product called 'True Black #5' sold by some jewelry supply houses that was excellent for turning N/S black.
But I don't see it for sale now taking a quick look around.
Maybe to dain'gous,,or the name alone sounded like it might be a bathtub gin and not FDA approved.
Might still be out there though. It was more than 10 or 12yrs ago the last time I saw it around.
Hope this helps.
