This is such an old and dangerous procedure that I don't know of
anyone who has ever used it. I think that today people oxidize or
enamel or even use the cold enamels to get the effect.
Well, now you do. I've found the stuff rather fun, now and then, and
a lot easier than black enamel, and quite different in appearance from
enamel or oxidized surfaces. It gives you a hard metallic black,
almost like hematite, flush with the surface. No enamel or oxidized
finish really resembles it all that much. Yes, niello is an old and
ancient process, but still widely used today, especially in india,
Bali, etc. In this country, in the sixties, the late Phillip Fike,
among a number of others, did a lot of research into the preparation
and use of niello, and taught it widely, though his classes at Wayne
State University in Detroit, and workshops around the country, until
shortly before his death a few years ago. So while you may not
personally know any niello users, I assure you there's a lot of folks
out there who do know how to use it. Yes, initial preparation of
niello is smelly and potentially toxic. So do as he did, and prepare
it out of doors. One relatively short session of such preparation can
make up more than enough of the niello to last you for years. Once
made, actually applying the stuff takes place at a low enough
temperature that no significant fumes of either sulphur or lead are
evolved. And I've seen pieces with the stuff, with a long history of
use and wear, with little enough degradation of the niello to suggest
to me that it's relatively stable, and not a dangerous source of lead
to the wearer either. Obviously, don't apply it to the skin side of
a piece of jewelry like the inside of a ring, or in wares designed for
food use. But I don't expect intermittant contact, such as with a
design on the outside of a ring, to pose any significant risk.
As to the role of lead in the recipe, it serves to make the resulting
niello softer and lower melting. It's thus much easier to apply, and
can be burnished more easily. The lead can still be a minority
componant in the mix, but it makes it a much easier material to use.
If this worries you, use less lead. If you want, mix it with just
copper and silver, but the resulting niello will be higher melting
and may tend to be pitty, from the sulphides breaking down again from
the higher temps required to apply and work it, and once applied,
will tend to be harder and more brittle. This is especially
significant in that burnishing a newly applied niello surface is an
important step to getting the best appearance, and is much easier to
do with a niello containing at least a little lead.
For good on how to prepare and use niello, see Phillips
chapter on the subject in "Metals Technic", edited by Tim McCreight.
Many of the other various jewelry making books out there also give
good info. One particular favorite is Herbert Maryon's classic
"metalwork and enameling"
Hope this helps.