Polishing gold plate

I had a sterling silver cast pin (professionally) gold plated some
time ago, and it is looking sort of dark and has lost it’s nice
shine. What is the best way to polish it? Can it be tumbled with
steel shot?? Rouge? I want to be careful not to polish away the gold.

Elegant Insects jewelry

DO NOT use steel shot unless you want to remove the plating. It is a
micro-thin deposition of gold on , in your case, sterling. Rouge is
even too abrasive. I would use 3M’s 6 micron radial bristle discs,
and remember it is rotation not pressure that makes any rotary tool
or flexshaft work well. So mount the disc, or use a psa disc of
similar grit and polish to a high gloss finish if that’s what you
want.Then re-examine how you are storing it. 3M also makes some
anti-tarnish strips you can add to a jewelry box or even a plastic or
cello bag for keeping- they are handy. If the piece is tarnishing to
a blackish colour it sounds like it’s near something sulfuric.
chlorine will alos turn gold, even Platinum with rhodium plating
black if splashed onto it. So after washing or a quick ultrasonic dip
and drying polish it with the above discs or even a polishing cloth
that is non-abrasive (being plated jewelry you are discussing- if it
were not plated an abrasive polishing cloth would be all that is
needed to restore the shine and in some cases,certain brands
deposit a film of anti-tarnishing agent on the piece ). rer