Justus Von Liebig and the modern process of mirror silvering.
In 1835, a German chemist and inventor, Justus Von Liebig, created a method of mirror making which involved depositing silver, instead of the previously used lead and mercury, on the rear surface of glass. After 20 years of work and improvements this method of mirror making gained wide acceptance throughout the industry. The method he created is the forbear of the process of ‘mirror silvering’ that we use today.
By 1930, an aluminium vacuum-deposition process for use in telescopes and other scientific instruments had been invented by John Strong, an astronomer and physicist from California University of Technology (Caltech). This invention led to the process we still use today.
In modern mirror silvering, whether using aluminium or silver it tends to retain this name, a sheet of glass is placed in a vacuum containing heated nichrome coils capable of evaporating the aluminium or silver being used. When in a vacuum the heated material travels in straight lines and upon hitting the surface of the glass cools and stick to it.
Some mirror makers place their mirrors in ovens and expose them to pure oxygen so the aluminium layer becomes oxidised, because aluminium oxide is more hardwearing than pure aluminium. Others evaporate a layer of quartz on to the mirror.