Are factory 360 Magnum pistons coated

Hey guys I've been cleaning up some factory 5.9 magnum pistons with oven cleaner. I've done in the past without any problems but this time I left them a bit long. the oven cleaner discoloured the pistons a little bit. if they coated pistons then I'll replace them but if they're not coated I'll use them. Does anyone know cheers