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When glass mirrors first gained widespread usage in Europe during the 16th century, most were silvered with an amalgam of tin and mercury, [6] In 1835 German chemist Justus von Liebig developed a process for depositing silver on the rear surface of a piece of glass; this technique gained wide acceptance after Liebig improved it in 1856.
The simplest optical coatings are thin layers of metals, such as aluminium, which are deposited on glass substrates to make mirror surfaces, a process known as silvering. The metal used determines the reflection characteristics of the mirror; aluminium is the cheapest and most common coating, and yields a reflectivity of around 88%-92% over the ...
A mirror reflecting the image of a vase A first-surface mirror coated with aluminium and enhanced with dielectric coatings. The angle of the incident light (represented by both the light in the mirror and the shadow behind it) exactly matches the angle of reflection (the reflected light shining on the table). 4.5-metre (15 ft)-tall acoustic mirror near Kilnsea Grange, East Yorkshire, UK, from ...
The optical glass available at the time tended to develop a tarnish on its surface with age, due to chemical reactions with the environment. Rayleigh tested some old, slightly tarnished pieces of glass, and found to his surprise that they transmitted more light than new, clean pieces. The tarnish replaces the air-glass interface with two ...
Mercury glass (or silvered glass) is glass that was blown double walled, then silvered between the layers with a liquid silvering solution, and sealed. Although mercury was originally used to provide the reflective coating for mirrors, elemental mercury was never used to create tableware.
The glass is most susceptible to breakage due to damage at its edge, where the tensile stress is the greatest, but can also shatter in the event of a hard impact in the middle of the glass pane or if the impact is concentrated (for example, the glass is struck with a hardened point).
Dielectric mirrors are very common in optics experiments, due to improved techniques that allow inexpensive manufacture of high-quality mirrors. Examples of their applications include laser cavity end mirrors, hot and cold mirrors , thin-film beamsplitters , high damage threshold mirrors, and the coatings on modern mirrorshades and some ...
Silvered glass mirrors were a vast improvement, since silver reflects 90% of the light that hits it and is much slower to tarnish than speculum. Silver coatings can also be removed from the glass, so a tarnished mirror could be resilvered without changing the delicate precision-polished shape of the glass substrate.