The magnet only eliminates most steel and iron. (Some stainless steel alloys are not attracted by a magnet.) Magnets are not a valid test except to find iron and steel items.

White metal base metal goods are more likely to be brass (a copper alloy), pewter (a tin alloy that might contain lead) or zinc. Nickel silver is a white brass. All of these metals can be silver plated.

Testing with nitric acid can indicate that there is a lot of copper in the alloy. In an inconspicuous part of the item make a deep scratch with a file or knife. Put a drop of nitric acid on the area. If it bubbles up green there is a lot of copper and the item is copper, brass or nickel silver. If it does not turn green and, when you rinse the acid off, the tested area is creamy white it is likely silver of at least .800 fineness. (80% silver.)

Watch for silver goods cast in India. We've tested several items that contained 30% cadmium and 65 to 70% silver. The Nitric test will not disclose that because there is not a lot of copper to turn green. The reaction of nitric acid with copper gives copper nitrate which is green

Pewter is quite soft, easy to bend. I don't know of an easy test for zinc.

BTW the steel parts of clasps are the springs inside. Silver does not keep a springy temper so steel or phosphor bronze is used for the springy parts.

Nickel is slightly attracted by a magnet. Brass goods with a nickel plate (even nickel under gold plate) will be *slightly* attracted by a magnet.

My dream CSI lab for jewelers includes an X-Ray def machine so I can just point, shoot and read out the metals involved.

If you want to see some of these tests in action search on youtube for "testing silver with acid."