I need a reference for an excellent gold plating company.
I use Gold Seal plating in Oakland, Ca. I’ve only had one experience plating about 1/3 of my inventory and it came out beautiful. I did have one problem with an earring that had the base of a post-style earring plated which caused one of my sensitive customers to return her purchase. Her ears got inflamed and painful probably due to the nickel content. When gold plating, the item must be plated first with nickel, then the gold. This prevents the gold from sinking and disappearing into the base metal underneath. This is an issue with all gold plating as far as I know, not the plating company. I got a much better price for a larger quantity of pieces, rather than just a few. --Susy
I don’t think this is correct. I was told that gold plating silver without nickel would cause the silver to oxidize under the gold plating. The nickel blocks the air from reaching the silver through the more porous gold plating. The disappearance of the gold on the surface is due to wear.
Tjones
Hi T, I’m repeating what I was told. I’m not that knowledgeable about that plating. Also, I’m plating over brass and copper, don’t know if that makes a difference. Susy.d
Nickel under the gold plating is to prevent the silver from oxidizing or otherwise gaining a patina. Though you might get some interesting rainbow effects before the silver goes all the way black. 
To keep atmospheric gasses from migrating through gold plating it must be quite heavy. The US Federal Trade Commission rules say that to qualify as vermeil the gold plating must be at least 2.5 microns thick, among other strictures.
I love Theta Plate in Albuquerque.