Clear mirror — the standard mirror that you probably have in your bathroom — comprises a clear pane of glass on top of a coated backing. The chemical backing is usually made from a base of silver and other minerals, and it’s this silver base that creates the reflective mirror surface. Clear mirror is available in a range of thicknesses, but it is usually comparatively thin — between 3mm and 5mm — to maximize light transmission and maintain a sharp reflected image. Mirror glass is most commonly made from basic annealed float glass, though other types of glass are also used in specialized applications.
Historically, mirrors were manufactured with copper bases, rather than the metallic coating that is used today. Because mirrors are cut to size after manufacture, the cutting and processing of mirrors often led to copper dust and other chemical residue being released into the air and eventually being washed down drains. While copper in and of itself is not toxic for humans, copper dust is highly detrimental to the environment and to animal populations. For this reason, many contemporary mirror manufacturers and suppliers have adopted strict copper-free policies.