Silver is one of the earliest metals used by humanity; today it is far more than jewelry and money—it is a critical material consumed heavily by industry. Electrical and electronic engineering is silver's largest industrial outlet: silver ranks first among all metals in both electrical and thermal conductivity, and silver pastes, silver contacts, or silver sintered layers appear in switches, relays, circuit breakers, photovoltaic cell grid lines, touchscreens, and flexible electronic circuits. Demand for silver contacts in high-voltage connectors, IGBT modules, and charging-pile contactors for electric vehicles has risen rapidly in recent years, and the photovoltaic industry has pushed silver-paste consumption to record highs. Although photographic film and paper have declined, in the film era silver halide light-sensitive materials were silver's second-largest use; today only motion-picture film, medical X-ray film, and professional photography carry it on. Jewelry, silverware, silver coins, and commemorative silver coins still steadily absorb a considerable share of silver, and sterling silver (925) is the most common jewelry alloy standard. Antibacterial action is another special niche for silver: silver ions inhibit bacterial growth, so silver is added to hospital dressings, antibacterial coatings in refrigerators and washing machines, water-purifier filters, food packaging, and baby-bottle linings.
Silver nitrate (AgNO3) is the most basic silver salt—a colorless, transparent crystal readily soluble in water. It is the starting point for preparing other silver compounds, silver-plating baths, and the silver mirror reaction, and historically was also used for eye drops in newborns to prevent gonococcal infection. Silver chloride (AgCl) decomposes under light to metallic silver and is one of the main constituents of the light-sensitive emulsion in photographic film and paper; it is still used in X-ray film, photographic paper, and certain ion-selective electrodes. Silver bromide (AgBr) has even higher photographic sensitivity and is the principal light-sensitive material of traditional camera film and graphic-arts film; the emulsion layer of color film is still based on it. Silver sulfide (Ag2S) is what causes silverware to tarnish and darken—a thin black layer formed when trace hydrogen sulfide in the air reacts with silver; it is also used as an infrared optical material and a solid electrolyte, and appears in certain sulfide solid-state batteries.
