Design

Mirrors are manufactured by applying a reflective coating to a suitable substrate. The most common such substrate is glass, due to its transparency, ease of fabrication, rigidity, and ability to take a smooth finish. The reflective coating ("silver") is typically applied to the back surface of the glass, so that it is protected from corrosion and accidental damage. Glass is much more scratch-resistant than most substrates.

In classical antiquity mirrors were made of solid metal (bronze, later silver) and were too expensive for widespread use, as well as being prone to corrosion. Due to the low reflectivity of polished metal these mirrors also gave a darker image than modern ones, making them unsuitable for indoor use with the artificial lighting of the time (candles or lanterns).

The method of making mirrors out of plate glass was invented by 16th-century Venetian glassmakers on the island of Murano, who covered the back of the glass with mercury, obtaining near-perfect and undistorted reflection. For over one hundred years Venetian mirrors installed in richly decorated frames served as luxury decoration for palaces throughout Europe, but the secret of the mercury process eventually arrived to London and Paris during the 17th century, due to industrial espionage. French workshops succeeded in large scale industrialization of the process, eventually making mirrors affordable to the masses, although mercury's toxicity remained a problem