US Patent 10072335 Method of coating of object

A method of coating a metallic object with a substantially invisible protective coating, wherein the coating comprises a first layer, a second layer, and a third layer, each layer comprising a metal oxide or a nitride. The method comprises placing the object in an atomic layer deposition (ALD) reactor; depositing a first layer comprising a metal oxide or a nitride on a surface of the object by ALD; depositing a second layer comprising a metal oxide or a nitride on the first layer by ALD; and depositing a third layer comprising a metal oxide or a nitride on the second layer by ALD, thereby forming the protective coating on the object.