In 1317 Venetian glass makers discovered the art of 'silvering' by applying a combination of mercury and tin to the glass surface. Six centuries later in 1840 the process of silvering, as we know it today, was patented.

The making of mirrors is one of the oldest techniques in the glass industry. The human need for mirror had an important impact on the manufacture of glass in general, because of the overriding requirement for parallel, optically flat surfaces, and glass of high quality. The mirror-makers of Venice established their guild in 1569, membership being secured by the flattening and polishing of a sheet of blown cylinder glass (see left picture), followed by the application of the reflecting leaf of tin-mercury amalgam (a technique developed in Venice 250 years before). A hundred years later, an equivalent guild was set up in England.

Up until the middle of the nineteenth century, mirror was made by floating glass on to tin foil coated with mercury. Then, in 1840, patent silvering was discovered. This involved chemical deposition. Typically, silver nitrate and a reducing solution were poured onto thoroughly cleaned, very high quality glass. Metallic silver was deposited on to the glass in a matter of minutes.

With the emergence of thin film technology, mirrors can now be made in a variety of ways, but many believe that perfect mirrors are still made by chemical deposition of silver, using the spray technique.