PNG images: Mirror
A mirror is an object that reflects light in such a way that, for incident light in some range of wavelengths, the reflected light preserves many or most of the detailed physical characteristics of the original light. This is different from other light-reflecting objects that do not preserve much of the original wave signal other than colour and diffuse reflected light.
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The first mirrors used by humans were most likely pools of dark, still water, or water collected in a primitive vessel of some sort. The requirements for making a good mirror are a surface with a very high degree of flatness (preferably but not necessarily with high reflectivity), and a surface roughness smaller than the wavelength of the light. The earliest manufactured mirrors were pieces of polished stone such as obsidian, a naturally occurring volcanic glass. Examples of obsidian mirrors found in Anatolia (modern-day Turkey) have been dated to around 6000 BC. Mirrors of polished copper were crafted in Mesopotamia from 4000 BC, and in ancient Egypt. These mirrors were from around 3000 BC. Polished stone mirrors from Central and South America date from around 2000 BC onwards. In China, bronze mirrors were manufactured from around 2000 BC, some of the earliest bronze and copper examples being produced by the Qijia culture. Mirrors made of other metal mixtures (alloys) such as copper and tin speculum metal may have also been produced in China and India. Mirrors of speculum metal or any precious metal were hard to produce and were only owned by the wealthy. These stone and metal mirrors could be made in very large sizes, but were difficult to polish and get perfectly flat; a process that became more difficult with increased size; so they often produced warped or blurred images. Stone mirrors often had poor reflectivity compared to metals, yet metals scratch or tarnish easily, so they frequently needed polishing. Depending upon the colour, both often yielded reflections with poor colour rendering. The poor image quality of ancient mirrors explains 1 Corinthians 13's reference to seeing "as in a mirror, darkly."
Glass was a desirable material for mirrors. Because the surface of glass is naturally smooth, it produces reflections with very little blur. In addition, glass is very hard and scratch resistant. However, glass by itself has little reflectivity, so people began coating it with metals to increase the reflectivity. Metal-coated glass mirrors are said by the Roman scholar Pliny the Elder to have been invented in Sidon (modern-day Lebanon) in the first century AD, although no archeological evidence of them date from before the third century. According to Pliny, the people of Sidon developed a technique for creating crude mirrors by coating blown glass with molten lead. Glass mirrors backed with gold leaf are mentioned by Pliny in his Natural History, written in about 77 AD. Because there were few ways to make a smooth piece of glass with a uniform thickness, these ancient glass-mirrors were made by blowing a glass bubble, and then cutting off a small, circular section, producing mirrors that were either concave or convex. These circular mirrors were typically small, from only a fraction of an inch to as much as eight inches in diameter. These small mirrors produced distorted images, yet were prized objects of high value. These ancient glass mirrors were very thin, thus very fragile, because the glass needed to be extremely thin to prevent cracking when coated with a hot, molten metal. Due to the poor quality, high cost, and small size of these ancient glass mirrors, solid metal-mirrors primarily of steel were usually preferred until the late nineteenth century.
Parabolic mirrors were described and studied in classical antiquity by the mathematician Diocles in his work On Burning Mirrors. Ptolemy conducted a number of experiments with curved polished iron mirrors, and discussed plane, convex spherical, and concave spherical mirrors in his Optics. Parabolic mirrors were also described by the physicist Ibn Sahl in the 10th century, and Ibn al-Haytham discussed concave and convex mirrors in both cylindrical and spherical geometries, carried out a number of experiments with mirrors, and solved the problem of finding the point on a convex mirror at which a ray coming from one point is reflected to another point. By the 11th century, clear glass mirrors were being produced in Moorish Spain.