Phil, the solder sold as IT solder by (for example) the Thompson
Enamel Co these days is the silver-copper eutectic alloy 72/28 weight
% silver/copper. It’s my understanding that this alloy is the one
used traditionally for sterling filigree (and hence plique-a-jour)
construction in Russia et al.
It would seem logical that this would be the silver solder of choice
for enamellers working with sterling. It has a Melting Point of 778
deg C and since it is a eutectic alloy, also flows at this
Up until I read in Glass on Metal some years ago that Valery
Timofeev made and used the silver/copper eutectic alloy as his solder
for plique-a-jour work I used Johnson Mathey’s JM11 extra hard IT
solder, and for some jobs still do. I bought a coil of it 20 years
ago from Silvercraft in Sydney (now long defunct) and still have a
metre or two left. Despite sporadic enquiries of JM and their agents
over the intervening years I’ve yet to find anyone who knows what I’m
talking about when I read them the label ( which is still affixed to
the original container ) - ah well!
Opi Untracht in “Jewelry Concepts and Technology” gives a formula
for and definition of IT silver solder: “IT - this is the solder
with the highest melting point. It is used for casework, and on an
object that will be enamelled after soldering. Enamelled metal
requires a solder that melts at a temperature higher than that needed
to fuse enamels, as otherwise the solder will reflow and interfere
with the enamel, possibly creating tensions that will cause the
enamel to crack. Care must be exercised in the use of this
high-melting solder as its flow point is close to (that of) sterling
Composition of typical IT solder: silver/copper/zinc : : 80/16/4.
Melting Point = 721 deg C, Flow Point = 810 deg C.