Why does silver tarnish?

The make up of sterling silver is 92.5% silver and 7.5% other metal (usually copper). Fine silver is 99.9% silver but is too soft for everyday wear. It's the copper in sterling silver that causes tarnishing, but it's needed to make the silver more hard wearing. There are several reasons why tarnish happens - sweat, water, food, perfume, swimming, creams - the list goes on! You can read more about it on the Birmingham Assay Office website here: https://theassayoffice.com/tarnishing_labexpert