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Repairing niello silver bracelet


#1

I am seeking advice on repairing a customer’s bracelet that is the
old silver, stamped made in Siam, style with niello. The tubing on
the hinges has broken off in several places. It is possible to solder
new tubing with hard silver solder without damaging the niello? If
not would something like a soft solder such as tix work? If anyone
has any experience working with this type of piece we would
appreciate advice.

thanks, charlie


#2

Find someone with a laser and use 14k PD white gold g wire to make
the welds.

James Binnion
James Binnion Metal Arts


#3
I am seeking advice on repairing a customer's bracelet that is the
old silver, stamped made in Siam, style with niello. The tubing on
the hinges has broken off in several places. It is possible to
solder new tubing with hard silver solder without damaging the
niello? If not would something like a soft solder such as tix work?
If anyone has any experience working with this type of piece we
would appreciate advice. 

To do a decent job on the tubes, and have any hope that the repair
will hold, you probably need something with the strength of silver
solder, rather than low temp solders like TIX or similar. Those are
better than ordinary plumbers/electronics soft solders in looks, and
somewhat better in strength, but they’re still basically tin solders,
and not very strong. the tubes wouldn’t hold too long.

Unfortunately, though niello can take some heat (it’s applied by
melting it on, after all), the heat of silver soldering is generally
too high unless the niello is far enough from the solder joint that
you can heat sink that area. Niello can be removed (scrape it out
after heating gently until it softens) and then reapplied after the
repair if you happen to have some niello around, or you can accept
that the overheated niello likely will be seriously damaged, or will
damage the silver. Neither is a good thing.

I’d say this is a good time to find someone with a laser welder or
PUK welder. Those methods can handle that repair easily, without
damage to the niello or the silver. (Contact me off list if you’ve
nobody local who can do it).

Peter Rowe


#4

Have you thought about soldering some tabs to the tubing and riveting
to the bracelet.

Tom


#5
It is possible to solder new tubing with hard silver solder
without damaging the niello? 

No don’t heat it ! Niello melts at a very low temp, its a lead,
sliver, copper alloy with a very low melting point. You’d probably
end up boiling the neillo and having it alloy with the surrounding
metals which would give you pits and all kinds of other nightmares.
I think a lot of those bracelets were made to sell more than to wear.
You might get by with cold connecting plate with hinge knuckles on
them and attaching them that way. The only heat repair would be to
remove all the neillo completely, as if you were dealing with lead on
silver, only then would it be safe to heat up. The Oppi Untracht book
has a good section dealing with it.

J.M Richardson


#6
Niello melts at a very low temp, its a lead, sliver, copper alloy
with a very low melting point. 

No, it’s perhaps worse than that. It’s what you get when you mix
those three metals, and then add sulphur, converting the metal to a
batch of mixed metal sulphides. Preparing niello thus ends up
smelling and looking a bit like a trip to the caverns of Hades
itself. Clearly a preparation process (making niello) best done
outside when there’s at least a bit of a breeze… The rest of your
description, though, what happens when overheated, is spot on. It
should be noted that heating per se is not bad. Melting the niello
into place on the silver is how it’s applied, where it goes on much
like one would flood an area with a low melting solder. It doesn’t
simply solidify, but rather goes through a substantial temperature
range where it’s solid, but plastic and malleable, so while at least
somewhat warm, you can burnish it nicely as part of the finishing
process. Once cold, it’s usually at least somewhat brittle, but you
can reheat it within the temperature range of Niello for things like
repairing the niello itself. Unfortunately, that temperature range is
a bit below the melting points of even the lowest decent silver
solders. But it’s higher than some people think. When you apply
niello, you use ordinary Handy white paste flux on the silver while
heating, and melt the niello onto the silver with the flux protecting
the metal and floating out of the way, just as it does with solder.
The trouble with heating it even slightly beyond it’s working
melting range is the sulphides start to break down again, with
significant formation of gas pockets and even flecks of metal in the
niello. Do that, and the best recourse is to scrape or grind it out
again, and reapply new niello. Really highly overheating it will
cause the lead content of the niello to attack the silver itself too,
and sometimes then you’d be needing to seriously repair or replace
the silver before being able to reapply the niello…

Note that there are many formulas used through history for niello
with differing percentages of the three metals. Some formulas even
omit the lead entirely, and these, which are harder both in actual
hardness and in how hard they are to work, also apply at a higher
temp, and might actually be able to withstand easier grades of
silver solder without needing more than simple reburnishing. But
that’s just a guess. (I’ve not dug through my old notes on the stuff
to try and find melting points), and it’s pretty certain that the old
Thai niello piece the OP was talking about most likely did not use
such a higher melting niello…

Peter Rowe