I think Peter makes a valid point: "there may be a difference
between the historical meaning of the term, which certainly does
specify the copper content, and the legal requirement that the base
metal MUST be copper and no other."
Let's check with the "experts"...
Oppi Untract (a European), in Jewelry Concepts and Technology, p.
44, in a paragraph describing British hallmarking: "Sterling silver
must contain 925/1000 parts silver; and Brittania, 958.4/1000 parts
silver, the rest usually being copper." There's an awful lot of
wiggle room between "must be" and "usually be."
Finegold & Seitz, in Silversmithing, p. 14: "In order to be made
harder and to wear better in general use, silver is frequently
combined with copper. This makes a binary alloy, a mixture of two
metals. (A ternary alloy would contain three metals.) When the ratio
between silver and copper is 925:75 the alloy is called sterling
silver." Might support your assertion that the alloying metal must
be copper to be called sterling, depending on interpretation.
Certainly opens up the possibility of alloying silver with metals
other than copper.
Interestingly, they also provide an alternate derivation of the word
sterling, aside from the German based Easterling. "A more plausible
derivation seems to be the Old English word Steorling - a coin with
a star - which refers to the small stars that appear on some Norman
Rio Grande catalog (yes, an American co.), 2002-2003, p. 35:
"Sterling silver is the term used to describe silver alloy that
contains 92.5% and 7.5% copper. Legally, 7.5% of any metal may be
used, with the product still marked 'sterling.'" They don't state
whether it's globally or domestically legal, but I suspect they ship
goods all over the world.
Last, but not least, from the U.S. Federal Trade Commission's
Guides for the Jewelry, Precious Metals, and Pewter Industries,
Effective April 10, 2001:
=A7 23.6 Misrepresentation as to silver content. (b) It is unfair or
deceptive to mark, describe, or otherwise represent all or part of an
industry product as "silver," "solid silver," "Sterling Silver,"
"Sterling," or the abbreviation "Ster." unless it is at least
925/1,000ths pure silver.
Of course, this just governs us silly Americans (what do we know?),
but again, nothing specifies what the other 75/1,000ths must be.
I've checked several other (non-American) resources, too, and none
of my research turns up anything that states specifically that the
alloying metal must be copper in order to use the term sterling.
The overwhelming evidence I find is that the degree of fineness
(.925) is the determining factor, with no stipulation as to the metal
with which the silver must be alloyed.
Phase diagrams are well and good, but I don't see how they would
support your position. If anyone has any documentation that silver
must be alloyed with copper to be deemed "sterling" in the global
marketplace, I'd love to see it.
All the best,
Sebaste Studio and
Carolina Artisans' Gallery
Charlotte, NC (USA)