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Gold alloy mix

Ok, I have dropped a clanger while re-alloying some gold and need
advice from somebody more knowledgeable in these matters than I
(that’s about everybody in here!) I was melting some customer’s gold
to cast a ring and since the originals were a mixture of 9ct and 18ct
yellow (all UK hallmarked) I added in some fine silver to get a 9ct
result. Having worked out the weights and melted and poured into water
in preparation for final casting (Delft clay system) I realised I had
forgotten all about the copper content! I have made an alloy that is
roughly Au 39 Ag 33 Cu 28 Whilst the colour seems fine to me would
anybody care to hazard a guess as to the working qualities of this
alloy since it seems Ag rich to me when compared to the recipes in The
Complete Metalsmith (excellent book - no connection etc.etc.) I can do
the sums to add pure copper and some more 18ct yellow to bring the
recipe back to something like 40 % Cu but do I need to?

I am gypsy setting a 7x5mm cab in the domed ring so don’t want a
really hard unworkable alloy. Dig me out of this one and I promise
to:- 1) not do my sums until I am awake! 2) stick to silver for a
while. 3) go and cut some opal - now that’s easy! Cheers

Andy Parker, Agate House Lapidary
Ulverston, Cumbria, England
Tel: 01229 584023

Not knowledgeable, but have the right book. “Precious Metals
Science and Technology” published by the International Precious metals
Institute " in an English translation from Japanese , copyright
1991, ISBN?. Expensive!

Pages 438-443. This is as hard as you would expect to get, as
annealed , in the K10- K9 series. Vickers hardness 120-130. tensile
strenghth at the peak and elongation at the minimum with respect to
copper concentration. Material can be age hardened at 300 C. Color
is Yellow.

I will try and photo copy the respective pages and send off line.

Hello Andy,

Considering the alloy you came up with it,you should not have major
problems with this alloy.Just whach your melting temperature and do
not overhead your metal.You’ve got lot of silver and copper in their
so cover the melt with charcoal or lots of borax to inhibit the
absortion of air to the metal and the oxidaton of the copper.Be sure
you’ve stired the melt with a grafhite rod to show up with
homogeneous alloy with a good workability.Don’t forget to anneal (not
to long or to hot)as soon as the item becomes workhardened and again
cover it with lots of flux.Don’t worry about the malability for the
setting just be sure to anneal the setting before the prepolish

Regards Pedro