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 sulphur in the air and copper in sterling silver that can cause tarnishing, but the copper is 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
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