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Pure silver is nearly white, lustrous, soft, very ductile and malleable. It is an excellent conductor of heat and electricity. It is not a chemically active metal, but it is attacked by nitric acid (forming the nitrate) and by hot concentrated sulphuric acid. It has the highest electrical conductivity of all metals, but its greater cost has prevented it from being widely used for electrical purposes. Silver is almost always monovalent in its compounds, but an oxide, a fluoride, and a sulphide of divalent silver are known. It does not oxidize in air but reacts with the hydrogen sulphide present in the air, forming silver sulphide (tarnish). This is why silver objects need regular cleaning. Silver is stable in water.
The principal use of silver is as a precious metal and its halide salts, especially silver nitrate, are also widely used in photography. The major outlets are photography, the electrical and electronic industries and for domestic uses as cutlery, jewellery and mirrors.
Both colour and black and white images have relied on silver since the early days of photography: silver bromide and silver iodide are sensitive to light. When light strikes a film coated with one of these compounds, some of the silver ions revert to the metal in tiny nuclei and the film is developed with a reducing agent which causes more silver to deposit on these nuclei. When the negative has the desired intensity, the unaffected silver bromide or iodide is removed by dissolving in a fixing agent, leaving the image behind.
Silver is also employed in the electrical industry: printed circuits are made using silver paints, and computer keyboards use silver electrical contacts.