A major mirror component is glass. Because glass is a poor reflector, it must be coated in order to make a mirror. The most appropriate materials for making metallic coatings are silver, gold, and chrome.
In classical antiquity, solid metal (bronze, later silver) was used to produce mirrors. The silvering process was invented in about 1600AD and is still used even today.
Glass is the main component of mirror. Because it is not a very good material for reflection, it must be coated with metal coatings, such as silver, gold or chrome.