I am a Metalsmith and I would suggest re-plating as your best bet. If you want a white/silver look ask to have it rhodium plated. If on the other hand you wish an antique look have it silver plated and let that oxidize.

removal of plating takes either abrasives < bad for a soft base metal/ pewter

OR a acid that will eat off the gold and copper < bad for your health and the base metal

OR electro stripping , which can use a acid as well



Personally I can never understand why so many of the items I see relating to our clothing addiction are made from what is in most applications a bad choice of metal. Buckles for example should be made out a metal that can resist fatigue and does not bend easily. I'll be honest and admit not having researched the historical buckle systems used but today a steel, silver, titanium, or other tough metal would be my choice for buckles and accessories .