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As a result of
discussions with Mel Bernhard of UPMR at the 1994 Santa Fe Symposium, it
was decided to develop a more useful firescale-free sterling silver.
Though the silicon-containing silver
alloy then used was certainly firescale-free, it was too soft for
practical jewellery purposes.
It was found, by the
addition of a small amount of germanium, that a more
acceptable degree of hardness was obtained while
maintaining the desirable firescale-free properties all silversmiths
were seeking.
Months of making and
testing many alloy combinations followed. We used germanium,
silicon and other elements to achieve the optimum firescale-free sterling
silver with working qualities as near as possible to standard sterling
silver.
Adding either silicon
or germanium alone to standard sterling silver will give a
firescale-free sterling silver (germanium is quite an expensive element,
whereas silicon is comparatively inexpensive). Silicon without germanium
will produce an unacceptably soft alloy. To achieve the best results with germanium alone,
at least 1.1% is needed but,
in combination with silicon, the amount of germanium required is
less than half, keeping the cost of sterling silver down.
The
hardness as-cast is a very acceptable 56HV compared to standard sterling
silver at 65HV. However, bright
sterling silver castings can be further hardened
to about 120HV by solution treatment. Wrought sterling silver will have a
hardness of around 140HV at 50% rolled, whereas bright sterling
silver, at 50% rolled, will harden to about 158HV. Additional benefits
of the new alloy included improved tarnish resistance and whiteness.
Apecs Bright Silver 925
G7 casting alloy was introduced for production casting
in 1997. As with any new innovation, this silver had
its establishment problems. During its
development, there were a number of occasions when the casting
quality was below the desired standard.
The first problem we noticed was a tendency for small nodules to form on
the
surface when soldering, as shown on the ring in Figure 1. When heated at
a temperature of approximately 700°C (1292°F), small nodules oozed from
the casting.
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