Silver

Silver holds records: the highest electrical conductivity and the highest thermal conductivity of any metal, and the best reflectance in visible light. Only its price stands in the way of wider use — and, in electronics, the fact that it tarnishes.

Chemically it sits in between: nobler than copper, distinctly more reactive than gold.

Native silver exists but is rarer than native gold. Most silver is recovered as a by-product, from polymetallic ores and in the processing of lead, copper and zinc concentrates.

Its own minerals are chiefly argentite, Ag₂S, and chlorargyrite, AgCl. The sulfide form is telling: silver binds to sulfur far more readily than to oxygen, and that is also why silverware blackens.

Silver has been known since roughly the fourth millennium BC. Unlike gold, it usually had to be smelted from ore, and mastering that process — cupellation, separating silver from lead by oxidising smelting — was a substantial technological achievement of antiquity.

The Latin name argentum gave the symbol Ag and, incidentally, a country its name: Argentina is named from the Spanish word for silver.

Silver does not react with atmospheric oxygen under ordinary conditions. It blackens because of hydrogen sulfide, which forms a dark sulfide, Ag₂S, on the surface. Traces of hydrogen sulfide are present in urban air, in egg white, in some cosmetics — hence the tarnished spoons.

In compounds silver is almost always monovalent. The photosensitivity of its halides is the practically important property: under light, AgBr decomposes and metallic silver is deposited. All of film photography was built on this — the latent image, development, fixing.

Silver nitrate, AgNO₃, is a classic reagent of analytical chemistry: it gives characteristic precipitates with chlorides, bromides and iodides, distinguishable by colour.

The largest consumer today is electronics and solar power: silver paste forms the contacts of photovoltaic cells. Then come soldering, mirrors and optical coatings, jewellery and tableware.

Photography, for decades the main consumer of silver, lost that role when photography went digital.

The antimicrobial action of silver ions has long been known and is used in dressings and water treatment. Moderation matters here: taking silver preparations systematically causes argyria, an irreversible grey-blue discolouration of the skin.