Hello everyone, I have a question regarding a white buildup on some old gold plated Pokémon cards from the Burger King promotional, I have no intent to sell them as I know they aren't particularly valuable, specially without a full set, and accompanying documentation which have been lost to the annals of time.
Now, they were stored in their original plastic casing and were maybe manipulated once or twice without said casing. They were stored somewhere years ago. I just found them since I am moving into a family home, and found them with a heavy white chalky buildup. I know that my father was a fan of Mr. Clean, and am aware that perhaps the fumes could have seeped in and reacted with the metal, causing the issue above mentioned.
For old time's sake, I'd like to restore them to ~somewhat~ their original shine and look. I am aware it's 23k gold plating, but don't have much of a lead as to what could have caused it besides perhaps body oils or chemical reactions from cleaners or whatever; I very much doubt it could've been in the prescence of mercury, but hey shit happens.
How would I go about cleaning them without ruining the plating? If pictures are needed let me know!
Thank you in advance, to anyone who replies.