Metals are opaque: they reflect light almost completely. For that reason they are utilized as mirrors; as films deposited onto a glass — you find them in any bathroom. If the metal film is very thin, the mirror is semitransparent. These half-silvered mirrors help to hide surveillance video cameras, for instance. One might think that holes in a metal film enhance the view. Exactly the opposite is true. Physicists discovered that tiny holes actually make the metal opaque.