This pendant is covered with a protective layer of laquer to maintain the colour of the metals as they are.  This should not be polished or put into silver cleaning solution or this layer will be removed.  A light buffing with a non abrasive cloth should be all that is required.

If the chain should require polishing then just stroke it with a polishing cloth or pad

Fine silver is 99.9% pure silver and is very resistant to tarnish.  Sterling silver is 92.5% silver and 92.5% copper which is stronger than fine silver but tarnishes easily.  Argentium sterling silver has some of it's copper content replaced with Germanium making it considerably more tarnish resistant than traditional sterling silver and just as strong.