Best sterling silver alloy to oxidize?

I have to make a few carved knife handles that I’ll cast in silver and oxidize so they’re mostly black except for the highlights. Is just straight Sterling Silver the best alloy to use for something that I’m hoping will retain its oxidation? I don’t do a ton with silver but I’ve been using various deox-sterling alloys for years to avoid oxidation, this is the first job I’ve had where the objective is to keep it black if possible. Thanks