No sure about your location but I searched dr google for "electroplating in Florida" and it came up with few choices. You might also find other businesses who offer same service under "metal finishing" or "metal plating" - just add your area of residence to the search. Depending on the value of the watch gold plating might set you back half the actual watch value to get it done. I've inquired for similar service but only once and have not done since. No Patek's here
Gold plating was usually done over a base metal case. Brass being the most common if not mistaken.
Same for gold fill which is thicker
Gold cap which is thicker than gold fill was usually bonded to steel
Now the process
Gold plate can be removed through a chemical process. Reverse of the application, but you can not replate over old plating
Gold fill can not be removed. In order to plate over gold fill. You would need to sand down any worn though areas in order to feather the gold fill into the base metal making the transition smooth enough that when plated you don't see where the gold fill ends and the base metal begins. Lot of work if a lot of worn areas, but not recommend on really worn cases. Just not worth it.
Gold cap. Can't remove. Rarely seen cases worn through due to thickness. Harder to sand down areas and make it look right
Cheap watch. Don't waste your time. Amount of time and cost is not worth it.
I did it once for a couple of little vintage Canadian Oyster models I had in order to sell them. Never bothered for anything else and tend to avoid gold plate/filled cases.
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