PVD, or Physical Vapour Deposition, is a method used to apply thin film coatings. The material used for the coating is vapourised in a vacuum and when the vapour condenses, the material adheres to electrically conducative material. By varying the gases and duration of the coating procedure on stainless steel, for example, a range of different colours can be produced, giving the appearance of bronze, gold and other metals. PVD can also be used to provide a black coating on stainless steel or titanium.
As well as being used for watch cases, PVD also has applications on much bigger objects. PVD coloured stainless steel is, for example, used as exterior cladding on the Vessel sculpture in New York City and The Bund in Shanghai. It is also used for the signature Space Gray and Gold finishes of the Apple iPhone X and XS.
PVD coatings are harder and more corrosion resistant than electroplating. The process is also more environmentally friendly than traditional coating processes such as electroplating and painting, since there are no toxic residues.