Marc, I use the following methods.
(1) Get a magnet-- if your metal is attracted, there is iron or
stainless steel there (the nickel in nickel-silver is generally not
enough to be attracted in a decisive manner, at least in my
(2) Get a little bottle of Silver Testing Solution. Mine is "JSP"
–can’t remember where I got it. Clean a test area, put on a tiny
– if it becomes creamy-colored, the metal is silver; if it turns
green, it’s base metal (brass, copper, nickel-silver). Rinse it off
immediately, and DON’T get the testing solution on you. It’s nasty
stuff. I assume that if you tested an intact piece of gold-filled
wire, it would also remain creamy-colored, although its interior
could be another matter.
Hope this helps