# Could the loss of mass in the kilogram be due to oxidation?

I was wondering about this. I have heard, and known for a while, that the famous and celebrated Prototype Kilogram - the lump of metal whose mass is used to define the standard mass scale worldwide - is slowly changing, degrading in some fashion, and this has prompted the search for a new and better definition of the kilogram mass unit on something more stable (the lead is now Planck's constant, but the change has not yet been adopted by the BIPM and looks like it won't be until at least next year.).

However what I'm curious about is the reason for the mass change. Apparently it's said it's not clear as to what exactly could be causing it, but I was wondering: is it chemically possible that this mass change could be due to oxidation - tarnishing - of the kilogram and removal of the oxide? I would imagine that the scientists who have studied this must have thought of this, so I'd be more interested in why it's dismissed as an explanation. In particular, it's said that the material it's made of - mostly platinum - has a very low oxidation rate, but "very low" need not equal "zero", and the mass change is reported as up to (unclear, because it's the measuring standard itself!) 50 micrograms over 100 years - which is nonetheless a very slow rate of loss - about $10^{-16}$ mol Pt/s, so that it would take $10^{16}$ s (10 Ps) to oxidize just one mole, or about 300 million years. Could this be within range of the very-slow-but-not-zero range of oxidization of platinum in air? In particular I find this: