Platinum doesn't oxidize, so chances are, they will not turn black. I own few platinum pieces from Tiffany and none of them turn black, but my silver pieces turn black since silver oxidizes. Yours look like is being tarnished, you can try to clean them at home first, this was how I cleaned most of my silver pieces. Fill a pot with water, heat to boil in low heat, then add a sheet of aluminum + a table spoon of baking soda then throw in all your silver pieces to remove the residues, let it boil for a minute. hope this helps