What makes a mirror reflect?

Mirror - it is the brightness of the mirror surface that makes it reflect light.
When light falls on a surface some of the light may be reflected or thrown back, some absorbed and some allowed to pass through. In a mirror the surface is made so bright that as much light as possible is reflected and as little as possible absorbed.
The earliest mirrors consisted of thin discs of metal, generally bronze, slightly convex and polished on one side.
The method of making mirrors by backing glass with thin sheets of metal was known in the Middle Ages, and a guild of glass-mirror makers existed in Nurnberg, Ger­many, in 1373. The commercial manufacture of mirrors was de­veloped in 16th Century Venice. Coated mirrors were made from blown cylinders of glass which were slit, flattened on a stone, polished, and their backs silvered by an amalgam of tin and mercury.
These mirrors had a high re­flecting power, but a considerable improvement came in France in 1691 when the art of making plate glass was introduced. The chemi­cal process of coating a glass surface with metallic silver was discovered by Baron Justus von Liebig of Germany in 1835. Mirror surfaces are used inside lighthouses, lightships and search­lights, where it is necessary to pro­duce a high degree of reflection in order to throw the beam of the light over a distance of several miles. Even a hand flashlight has a slightly mirrored surface behind the bulb.

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