Mirrors have a long history of use in human society, from the earliest polished reflective surfaces made from obsidian (volcanic glass) used thousands of years ago to the most modern wall and handheld mirrors today. Mirrors have been made from rock, wood, and many metals over the course of history. In ancient Mesopotamia (modern-day Iraq and Iran), polished copper was used as a reflective metal to provide a mirrored surface, while in ancient Egypt and medieval Japan, circular golden or bronze mirrors were given religious and cultural significance, associated with deities of the sun.
Each different metal has its own individual properties. Some may be too soft to use effectively, or too expensive to be economically viable. But of particular interest to mirror-makers is the reflectivity of the metal. Different metal coatings will reflect light more or less effectively and may be better at reflecting certain wavelengths of light, but not others. The function of the mirror is of utmost importance, as reflectivity may take precedence over durability, or vice versa.
Silver metals, like aluminium, beryllium, and silver itself, are favoured for mirrors requiring the best reflection of the spectrum of light visible to humans. Golden-coloured metals like copper and gold are best at reflecting red and infrared wavelengths of light. The most common metal to use for a standard reflective mirrored surface is aluminium, due to its relative stability and endurance, but aluminium does suffer a dip in reflectivity of wavelengths of light between 0.8 and 1.0 micrometres (μm). Silver is much more consistently reflective above 0.3μm, but dips nearly to 0 below that, making it wildly unsuitable for reflecting the ultraviolet range and thus, inappropriate for use in astronomical telescopes.
For some situations, higher durability is favoured, and less reflectivity can be tolerated. For example, dental mirrors are made of an exceptionally rare mineral called rhodium, which isn’t as reflective as silver but is far tougher and better suited for dental use. Similarly, mirrors used on car rear-view and wing mirrors are made from chromium, which has similar properties, but is incredibly toxic. Wouldn’t want the dentist popping a chromium mirror into your mouth! Silver can’t be used in these situations because it tarnishes quickly, depending on environment. In a dry place with no contaminants, it may last a while, but in humidity will deteriorate quickly. For example, a silver mirror may last months in Albuquerque but degrade within just a day in Orlando.
If you’re in the market for a new mirror or some mirrored furniture, come take a look at William Wood. We only ever use the best materials for the job so you know you’re receiving a top quality, lasting product.