Personally, I'd use the "Scourgify" cleaning spell. Hermione used it once to clean out Hedwig's cage. It works great! And you don't have to worry about using obsolete Muggle methods, which will surely damage the surface, leading to net or details grade when you send it to the grading service. If you combine this with the "Reparo" spell, it may return it to its original mint state condition, possibly getting you an ms65rd grade from PCGS. Or, it might just turn it into a real Indian, in which case, I would be ready to cast an "Avada Kedavra" spell just in case!