Can certain kinds of coatings make sterling silver jewelry attract to a magnet?

Question

Can coatings such as a rhodium coating cause sterling silver jewelry attract to a magnet? What other variables can cause silver jewelry to attract to a magnet?

What kinds of home tests can you do to test metal purity that won't damage the jewelry?

Answer 1

You could try to weigh the jewellery, but that's probably going to be hard to get accurate results because the exact composition isn't usually a readily available fact and the existance of other materials (stones etc) which you can't take out readily will skew results ...

Maybe an electrical conductance test would work, maybe a small battery connected across the piece of jewellery could get you a reasonable estimate, though you'd need to work out the effective resistance of the shape of the piece of metal, which is going to be non-trivial to say the least, so that you can work out what the R-value should be, vs what it is given the published material consistency and published resistance values for the metals and other materials which are present in the piece.

Answer 2

The most likely explanation for the magnetism is that the jewelry is made of silver plated onto a magnetic metal, possibly steel but more likely a nickel alloy.

I don't think rhodium is ferromagnetic, and even if it were, the amount applied to the jewelry would be too small to cause a noticeable attraction (rhodium isn't exactly cheap - only a very thin coating would be applied).

So the ring is most likely not solid silver, as sterling silver is an alloy of silver and copper, and silver is not usually alloyed with magnetic metals.

Beyond this, testing the metal purity at home is very difficult for silver jewelry without damaging it.  You could try scraping away some of the metal on the back of the piece (to remove any platings) and checking if it tarnishes (if there is a rhodium plating, the jewelry might not tarnish).  You can expose it to hydrogen sulfide to speed the tarnishing - use a rotten or boiled egg.  If the scraped area tarnishes, there is silver there, so it is likely that the ring is solid silver.  If the rest of the piece tarnishes, but the scraped spot does not, it was only silver plated.

The best non-destructive way to test the purity of metals is XRF (x-ray fluorescence), but this is not something you could do at home, and testing the underlying metal would still require the platings to be removed.

The conductivity idea is intriguing, but if it is, say, an earring instead of a ring, calculating the ideal conductivity will be very hard.  Silver is the most conductive metal, so a less-than-expected result would most likely indicate the presence of other metals (though sterling silver is not supposed to be pure silver, and tarnish layers could increase the resistance...)

EDIT: I should add, if this is an earring, it is possible that the post and other parts (especially if it contains a spring) could contain steel or other ferromagnetic metals, even if the rest of the jewelry is sterling silver.  Silver is too soft to use in such parts, so you should check if this is the case.