Surface Oxidation of Vitamin C

Sorry no idea.

Well it might help if you just reveal which product that you mention here dear. Maybe anyone else shared the same reaction as yours? But all I know vit c formulation has two sides. The stable ones which tends to be vit c derivatives and the pure vit c form which tends to higly photosensitive( they oxidize faster in presence of light). I havent use that much of vit c products so I cant say much about this but my rule of the thumb is if it comes in darker bottles they usually will require more thorough care( need to keep in skincare fridge and shorter pao).