The concern is metal purity, if you want to call your alloy
sterling, and stamp it as such.
As you know sterling silver is .925 fine silver content (well this
is what it is in Australia), and to stamp an alloy .925 (in
Australia) you must have that percentage of fine silver, the other
element is usually copper. If you create a silver alloy with more
copper then you bugger the .925.
If you are just after a different silver alloy, then you can look at
the mokume alloys, the one I like is 25% fine silver, the remainder
of the alloy is copper.
James Binnon could possibly offer some suggestions for you.
Regards Charles A.