The basic sputtering process involves a large vacuum chamber and an inert (or reactive) gas atmosphere as well as electrical energy. The electrical energy imparts a negative charge to the atoms or molecules of the gas. The vacuum pressure (which is extremely low compared to normal atmospheric pressure) allows the negatively charged particles to move freely around the chamber at high velocity. When those charge particles strike a cathode (which is the metal that is going to be applied to the film), atoms of the metal (or metal-oxide) are dislodged from the cathode, also at high velocity. These strike the film substrate, creating a thin layer of metallic oxide. Sputtering is a versatile process as several layers of film (metal on metal layering) resulting in unique colors an higher levels of selective transmissions.