- Is it OK to mix Sterling and Fine Silver scrap for melting down?
Mixing fine silver and sterling works just fine, but what you’ll
then have won’t be either sterling or fine, but something in between.
Less likely to tarnish, a bit softer, and with a higher melting
point. But it should cast just fine. If you get the mix right, it
will be close to “brittania” silver, which is 950 silver, instead of
sterling’s 925.
2. Can Sterling scrap from old castings be used, or would it be
too brittle?
Unless your scrap is contaminated with other metals, especially
things like lead, tin, or the like, there’s no reason why it should
make the casting brittle. What may happen, though, is that it will
already have a higher amount of oxides, so your castings may also
have more oxides, with resulting porosity. But much depends on how
you melt. If you’ve got a soft gentle (reducing) flame, it can remove
much of the existing oxides, and combined with the use of a bit of
melting flux (mix one third to one half borax with one half to two
thirds boric acid powders. use just a little) This assumes, fo
course, that you’re using just standard sterling silver, not a
specialized casting alloy which may have deoxidizers. Most
deoxidized casting alloys DO allow you to mix old castings with new
metal, but specify the maximum allowed amounts of old metal.
3. I'm assuming that scrap that has solder in it should not be
used, but is that correct?
Well, this gets in to a more grey area. If the solder you use is
good silver solder, especially in medium, hard, or IT grades, AND if
in melting you make sure the whole melt is thoroughly mixed, then
you’ll likely have few problems. It might give you, as with old, bad
castings mixed with new metal, increased porosity, depending on how
much solder you’ve mixed in. The problem is that the solder’s
contain zinc, which when overheated, can volatilize, causing gas
porosity. or defects in the casting. But if you melt properly, it
shouldn’t cause undue problems. Zinc is often added intentionally as
a deoxidizer to gold alloys, and can function similarly here, if
you’re careful in melting. . (If your scrap has "easy flo, and
perhaps even some brands of “easy” solder, then it’s probably not as
good an idea to mix it, as the zinc content is higher, and with “easy
flo”, some contains cadmium too, which is NOT good to mix in. But if
you’ve only got a small amount of higher grade silver solders in a
considerably larger amount of sterling or sterling with fine silver
AND you take care not to greatly overheat the melt, then likely as
not, the traces of zinc you’ve included from the solders may not make
much difference to the quality of the casting, and may even make the
melt very slightly easier to melt. Of course, just as with adding
fine silver, the precise silver content will be thrown off by adding
solder containing scrap. Whether it’s significant or not depends on
the quantities, and your end use.
Peter Rowe
