Master Replica Plaques - Problems

[FETTFAN]

I have recently experienced problems with the Signature edition plaques for both Luke, Vader and Dooku, which look as if the problem has been caused by oxidation. I believe most of the first edition plaques suffered from this and I was just wondering the best way to treat this. Thanks for your help in advance

[Darth Pain]

Hmmm..I think, I read somewhere that Baby oil works well with that. It's Aluminum correct? White oxidation?