Silver (Ag)

Silver holds three separate records in the periodic table simultaneously. No element conducts electricity better, none conducts heat better, and none reflects visible light better. That is an unusual clean sweep, and it comes from a single cause: a full 4d shell beneath a single loosely held 5s electron, giving a sea of highly mobile carriers and very little to scatter them.

What is striking is how little of that matters commercially. Silver's conductivity beats copper's by only about five per cent, and silver costs vastly more, so almost every wire in the world is copper. Silver is used where five per cent decides something, where the connection is tiny, or where nothing else survives the environment — which turns out to be an enormous number of places, just never a heavy one.

Argentum, and the only country named after a metal

The English word descends from Old English seolfor through a Germanic root shared with Dutch zilver and German Silber, of uncertain earlier origin. The symbol comes from a different family entirely: Latin argentum, which traces to a root meaning white or shining and gave the French argent, still the ordinary word for both silver and money.

Argentina takes its name from that root, by way of the Río de la Plata — the river of silver — which Spanish explorers named for the metal they hoped, wrongly, was flowing down it. It is the only country in the world named after a chemical element, and it was named after silver it did not have.

Laurion, Potosí, and the money of the world

Silver has functioned as currency for longer and more widely than gold, because it is common enough to buy a day's bread with.

In 483 BC a rich new vein was struck in the Athenian silver mines at Laurion. The assembly's instinct was to distribute the windfall to citizens; Themistocles argued instead for spending it on two hundred triremes. Three years later that fleet destroyed the Persian navy at Salamis. The argument over a mining surplus is as close as antiquity comes to a decisive fiscal decision.

The larger episode is Potosí. The Cerro Rico in what is now Bolivia, worked from 1545 under the mita system of rotating forced indigenous labour, produced silver on a scale that had no precedent — enough to remake the finances of Spain, drive inflation across Europe, and, shipped west on the Manila galleons, to become the effective currency of Ming and Qing China, whose tax system had shifted to silver payment. The Spanish eight-real coin circulated from Boston to Canton and is the ancestor of both the US dollar and the peso. Estimates of the human cost at Potosí over three centuries run into the hundreds of thousands.

The British pound preserves a fossil of the same logic: a pound sterling was once literally a pound weight of sterling silver, and the currency's name is a statement about mass.

Silver Thursday

The last serious attempt to control the silver market ended on 27 March 1980. Nelson Bunker Hunt and William Herbert Hunt, heirs to a Texas oil fortune, had spent the 1970s accumulating physical silver and futures contracts on an extraordinary scale, and drove the price from around $6 an ounce to nearly $50 in January 1980.

The exchanges changed the rules, restricting new long positions and raising margin requirements. The price fell by half in four days, and on Silver Thursday the Hunts could not meet a margin call of over $100 million. The collapse threatened the brokerage that carried them and required a bank consortium loan to contain. Silver did not return to $50 in nominal terms for thirty years, and the episode is still the textbook case of what happens when a corner meets a rule change.

From film to photovoltaics

Photography was where the bulk of it went for a hundred years. Silver halide crystals in a gelatin emulsion are exquisitely sensitive: a few photons create a latent image of a handful of silver atoms, which development amplifies into a visible grain. Digital capture removed that market almost completely in about fifteen years, and with it a substantial supply of recycled silver recovered from film and fixer.

What replaced it was solar power. A silicon photovoltaic cell needs metal fingers on its front face to collect current without shading it, and those fingers are screen-printed silver paste, fired into the cell. Manufacturers have thinned the lines relentlessly, but the newer cell architectures now taking over — TOPCon and silicon heterojunction — need more silver per cell, not less. Photovoltaics is now the largest single industrial consumer of silver, and the amount of silver available has become a genuine consideration in projections of how fast solar manufacturing can grow.

Beyond that, silver goes into electrical contacts and relays, where its oxide conducts (unlike copper's, which insulates and causes contacts to fail), brazing alloys, conductive inks and RFID antennas, and silver oxide button cells.

The catalyst with no substitute

Ethylene oxide is made in one way and one way only: passing ethylene and oxygen over metallic silver on an alumina support at around 250 °C. Every other catalyst that has been tried burns the ethylene to carbon dioxide instead. Silver, uniquely, holds atomic oxygen on its surface in a form that adds across the double bond rather than tearing the molecule apart.

Ethylene oxide is the feedstock for ethylene glycol — antifreeze and polyester — and for surfactants and sterilants, and it is made in tens of millions of tonnes a year. It is one of the few cases in industrial chemistry where a precious metal is genuinely irreplaceable rather than merely best.

Why it blackens, and why a few people turn blue

Silver does not rust, and it is not oxygen that tarnishes it. Silver reacts with trace hydrogen sulfide in the air to form silver sulfide, a black film — which is why silver tarnishes faster in industrial air, near cooking eggs or onions, and in rooms with wool carpets, all of which release sulfur compounds.

Silver ions are toxic to bacteria at low concentration, an effect known since antiquity and exploited today in silver sulfadiazine burn dressings and antimicrobial coatings on catheters. Ingested colloidal silver preparations sold as remedies have no demonstrated benefit and one distinctive consequence: silver deposits in the skin and is reduced by light to metallic particles, producing argyria, an irreversible slate-blue-grey discolouration of the skin and eyes.

Silver-107, and a clock inside iron meteorites

Silver's two stable isotopes are nearly equally abundant, silver-107 slightly ahead of silver-109. That near-parity is why the atomic weight sits close to 108, between two odd mass numbers.

Silver-107 has a secondary significance in cosmochemistry. Palladium-107 decays to it with a half-life of about 6.5 million years, so the solar system's original stock ran out long ago. But iron meteorites that separated metal from silicate very early trapped palladium without silver, and they now carry an excess of silver-107 in proportion to how much palladium they contained. Measuring that excess places core formation in those meteorites' parent bodies inside a window only a few million years wide, right at the beginning.

Most silver mined today is not mined for silver. Around three-quarters of world production comes out as a byproduct of copper, lead-zinc and gold operations, with Mexico, Peru and China leading output — which means, as with several of its neighbours, that supply responds to the price of other metals rather than its own.