Quote Originally Posted by tonyfoale View Post
Thanks for that. So contaminants are loose particles?
Yes, contaminants come in many forms but are typically undesirable particles that land on the surface being coated that then cause voids in the coating surface. These can also be introduced by debris left on the lens (or whatever is being coated) from improper/incomplete cleaning prior to coating or even from leaking seals on the vacuum pumps. There are a 100 ways a coating run can get messed up. Your iridium helmet shield is an example of a thin film deposited coating.