On Fri, 16 Jul 2004 07:40:57 -0700, in ¤ô Jack Schmidling wrote:

I have been thinking of casting a chalice in sliver in addition to making
some broach-like settings. I am set up to do sand casting and can probably
finish the stuff off in the machine shop.

I have a number of 100 oz ingots of .999 bulion to play with but suspect
that one does not want to use pure silver for this sort of stuff.

Can someone provide me with some alloying info to get something like
sterling?

Is this really necessary?

js

Recent threads suggest that it's pointless for us to suggest that sand casting
an item of this size may be less successful than you hope, given that silver is
more prone to problems with shrinkage porosity than some of the other metals you
might be sand casting. But if you use plenty of sprues (or gates, if you like),
and the thickness of the chalice you use as the model is not too thin, you might
get sucess. And of course sand casting is easy enough to try over and over till
it works, at little expense other than the silver itself, so I'd say, "go for
it". Not much to lose if you've already got the setup. Sterling silver melts
at around 1640 F, and you'll want it around a hundred degrees hotter than that
to pour, I'd guess... Be sure to use some boric acid powder or a mix of boric
acid and borax, as a melting flux, to help control oxidation when you melt.
Thin sheet metal forms will be difficult to get to fill well, unless you have
the metal at a seriously elevated temperature when you pour, which can increase
problems with porosity. But if you've already got the setup, then it's easy
enough to try, and of course, any silver scrap you generate can easily enough be
remelted, or sent for refining.

The alloy normally used as sterling silver is 7.5 percent copper, with the
balance being pure silver. Be sure to use good pure copper as the copper
source. i've always used scrap copper electrical wire, which works just fine.
If you want to get fancy, there are proprietary silver alloys out there which
use other than copper, in order to reduce fire scale/oxidation problems on the
silver when casting. These tend to produce a softer alloy than sterling, but
may be worth investigating. I don't know if they are available as "master
alloys which you'd add to pure silver. suspect not, but worth asking. United
Precious Metals is the main supplier I'm aware of for these alloys. As I said,
the exact formula for them is proprietary, so I can't give you that composition.

Hope this helps, and have fun. let us know how it turns out, will you?

Peter