This is an interesting thread. Now I've been reading the books
that other people had sent me, and I understand there is a mixture
known as "niello", being composed of silver, lead, and sulfur, that
is used in contrast with metals in jewelry.
Usually it also has copper, and some formulations don't have the
lead. Niello has a long and rich history, and is still used widely in
some other parts of the world. But it's application doesn't lend
itself as well to commercial mass production, so you don't see it as
much in the "west". But you can find various artists, some here on
Orchid, who'll use the stuff now and then. I've used it myself now
and then when it seemed the right material for a given design. At
one time, it was very frequently used in some Asian work, especially
Thai and Indian work. Less so today, mostly because it's more work
and more cost than resins, paint, or enamels. But you can still find
it's use easily enough if you look around in that part of the world.
Here in the U.S., the late Phillip Fike, who taught at Wayne State
University in Detroit for decades, championed the rediscovery and
exploration of Niello among American craftspeople, and though he's
passed on now, many of his former students still use the stuff. You
can find a fine write up of the process in "Metals Technic", edited
by Tim McCreight, as well as in Oppi Untracht's two books, and a
number of other references.
Of course, lead is far too toxic to use casually these days, which
is why I suppose we don't see niello in current jewelry...
All the metals, silver, copper, and lead, in Niello, are converted
to a mix of metal sulphides (just as the tarnish on sterling silver
is black silver and copper sulphide). It doesn't have the same
toxicity issues as metallic lead does, at least not in finished
jewelry (though I wouldn't suggest sucking on the stuff like candy,
and it's not a good choice for children's jewelry or for application
to surfaces that are in direct continuous contact with skin like the
inside surfaces of a ring shank...) The main toxicity issues are in
the initial preparation of the stuff. messy, smelly fumes, it needs
to be done outside in a decent breeze. Once made, it's easy enough to
apply without toxicity problems, so long as you don't grossly
overheat it.. In use, it shares many of the uses and visual
characteristics of black enamel, with subtle differences, and it
remains slightly plastic, like a softer metal (part of the
application process is burnishing, just as might be done to metal),
so it's durability is quite different from hard but brittle enamels.