I have airbrushed several helmets, I would recommend using a primer with either enamel or lacquer paints. Enamel is what I started out with and have had no problems with the helmets. I just started with lacquer paints and you must use a good primer with them otherwise they will deteriorate the helmet. I do prefer the lacquer because the pearls and pearl powders I use really make a difference. But so far I haven't heard of or seen any problems with them, however make sure the helmet is protected in the bat bag if used, otherwise it will get chipped and scratched. Hope this helps.
