Brass is non-magnetic. If you are able to get a magnet to stick; it is plated and not solid.
While I’m at it – all sterling silver is required to have .925 stamped somewhere. Otherwise, it’s just plated. Fine silver (like your family’s fancy silverware set) is .915, the softer alloy (rolled with less of another metal such as rhodium, from the platinum family).
Might seem boring but for those of you with allergies to plated materials and nickel, if you follow my rules you’ll be just fine!