Peter W. Rowe wrote:
There are two issues here.

One is the metal itself. Modern silver is generally sterling silver, which
contains 7.5% copper. Old silver may have less copper, or even traces of gold,
since the two metals are often found together, or one impure with the other,
etc., and ancient refining methods were often somewhat less than perfect. As
well, if the ring was buried for a time, there may well have been a good deal
of leaching of the copper, if any, that might have been near the surface, out of
the metal, leaving the surface area purer silver than the main body of the
metal. And ancient metalworking methods, principally heating and working
without the benefit of good firescale preventing fluxes, would also tend to lead
to a final object who's surface was copper depleted. Since the copper in
sterling tarnishes more rapidly than the silver (though both form black
sulphides), items with that sort of close-to-fine silver surface, would tarnish
more slowly. Traces of gold in the alloy, if any, would make it tarnish even
more slowly.

Even with pure silver the metal "yucks" up pretty quickly.

I just don't understand how this ring, which would have been cast, due
to its design, in only just yellowing now. It's been in the atmosphere
for some time now.

One of the interesting things about the old casting methods, and when I
mean old I'm referring to viking dark age casting methods.

The silver poured into the moulds would have come out fire scale free,
or so the modern experimental archaeologists have show with their work.

The interesting thing is that usually small amounts of metal were
melted, in charcoal (so a reducing atmosphere), and the lost wax moulds
used were made from clay mixed with horse dung.

I'm wondering if the use of base materials, as opposed to refined
investment plasters, would make a big difference? I haven't been
forwarded any answers yet from the archaeologists.


Regards Charles