I have the plastic gold grapes that I have used on 50th Wedding Anniversary Cakes. I've had the grapes a few years. I have an order coming up for another 50th Anniversary and they want the gold grapes. I noticed when I pulled them out this time, they are looking dull and a little "tarnished." I was wondering if anyone knows anything food safe that I can do to give them their sparkle and shine back? Thank You.

You can try spraying it with gold lustre dust from PME.

Have you tried washing them w/a bit of mild soap & warm water?
I like bashini's suggestion.

I did try cleaning them, but they have a very tarnished look and it didn't help at all.
I've never used Luster Dust and I didn't know if it would adhere to plastic or not. Guess I'll be trying it, though. Thank You.

luster dust is an extremely fine powder and seems to always cling to everything. so, i'm sure you'll be able to give some sparkle to your grapes.