Does anyone have any recommendations from personal experience
about which product is actually good at blackening high karat gold"
I've tried one product that said it would work on gold, but did a
wretched job... I know it can be done somehow, as I've seen
blackened gold jewelry for sale...
Those oxidizing solutions that claim to work on gold only do so
decently on up to about 14K. They require being heated, and applied
with a steel or iron tool for best color, and the result is a
somewhat metallic dark color rather than a good uniform black. They
don’t seem to work on higher karats. This is because anything that
want’s to actually oxidize the alloy is working with the portion of
the alloy that is not gold, and with high karat golds, there’s just
not enough alloy exposed for a good black, usually.
Enamel, Niello, or a resin version of enamel (like ceramit) can give
you good black color if you’re filling a recess.
If you’re just trying to color the metal surface without covering it
with a significant layer of anything, (ie you want a patina), your
options are more limited. The commercial “antiquing” products that
will give you the best blacks are essentially paint. They do work
reasonably well, especially with recessed areas.
Actually oxiding high karat gold is difficult to impossible
(depending on what you are talking about as high karat) but you can
get a black metallic looking surface with electroplating. Black
Rhodium, which gives a sort of metallic darkish gunmetal color rather
than a true black, is perhaps the most commonly used, and probably is
what you’ve seen in other products doing this. Relatively durable,
though of course it’s still just a surface finish that can be
removed. A better color, ie a deeper black, especially a matte black,
is probably a black nickel plate. These seem a bit more difficult to
get to work well, and the plating seems to be more fragile.
You also have a simple option of copper plating the surface, and
oxidizing the copper surface, same as you would with solid copper or
sterling silver. This has the disadvantage of introducing more base
metal into the surface, but you simply polish off the copper that you
don’t want blackened, again exposing the gold
And there are some higher karat alloys made that specifically are
intended to be blackened. Argen sells an 18K yellow gold that, after
fabrication etc, is heated to a low red heat, in air, and slowly
cooled. The result is a decent oxidized black color. This has the
advantage of being easy to do, or later redo, so long as you don’t
have anything in the finished piece that can’t be heated red hot.
Kinda makes black metal around your diamonds a poor prospect for
this material, but for some stuff, it’s an easy way to do it.
And there are also some high tech approaches. Class ring
manufacturers used to use the black paint on products, but in recent
years, seem to be doing it with a much more durable coating. I’m told
it’s a ceramic sort of coating, or perhaps a vapor deposition
coating. Either way (or maybe it’s both. Don’t know), that’s tough
and durable, and does the job. That way would work on virtually any
metal, even pure gold. But it doesn’t sound like the sort of process
suited to a small shop…