Zinc (Zn)

Zinc was the last of the common metals to be produced deliberately, and the reason is a collision between two temperatures. Reducing zinc oxide with charcoal requires something above 1000 °C. Zinc boils at a little over 900 °C. In an open furnace, the metal is therefore already a vapour at the instant it forms, and it leaves up the chimney and burns back to a white oxide smoke in the air above. Mediaeval European metallurgists knew this smoke well and called it philosopher's wool. What they never got was a metal.

Distillation, not smelting

The only way to obtain zinc is to condense the vapour somewhere sealed and oxygen-free, which makes zinc production a distillation rather than a smelting operation. That is a conceptually different process, and it needs different apparatus.

The apparatus was built in Rajasthan. At Zawar, in the Tiri valley, the hillsides are covered with the debris of an industry: banks of small square furnaces and enormous dumps of spent clay retorts. Each retort held ore and a reductant, sealed, with a narrow tube pointing downward into a receiving vessel below, so that zinc vapour travelled away from the heat and condensed as liquid metal out of contact with air. The mediaeval Sanskrit texts describe it as tiryakpatana yantra — distillation by descending. Radiocarbon dates place industrial-scale operation from around the twelfth century CE, with mining at the site going back much further, to roughly 750 BCE.

Europe arrived at the same answer six hundred years later. William Champion patented a downward distillation process at Bristol in 1738, and it is essentially the Indian method; how much he knew of it is debated, but Indian zinc was reaching Europe as a traded commodity by then. Andreas Sigismund Marggraf published a clear description of isolating and identifying the metal in 1746 and is the name European sources usually attach to the discovery. The card above gives the 1746 date without a discoverer, which is about as honest as a single line can be.

Brass for two thousand years without the metal

None of this stopped anyone from using zinc. Roman brass was made by cementation: copper metal and calamine — a zinc carbonate ore — were sealed in a crucible with charcoal and heated, so that zinc vapour was generated and absorbed directly into the solid copper without ever existing as a separate substance. The Romans standardised the sestertius and dupondius in this alloy from the first century BCE.

An entire alloy industry therefore ran for two millennia on an element nobody could isolate, possess or name.

Built to be destroyed

Over half of world zinc production goes into protecting steel from corrosion, and the mechanism is frequently misunderstood as a barrier coating. It is not primarily a barrier. It is a sacrifice.

Zinc is anodic to iron, meaning that when the two are electrically connected in the presence of moisture, the zinc corrodes preferentially and the iron does not corrode at all. The consequence is that a scratch in galvanised steel does not matter: bare steel at the bottom of the scratch is cathodically protected by the zinc surrounding it, and the coating slowly consumes itself to keep it that way.

The contrast with tinplate makes the point sharply. Tin is cathodic to iron, so a tin coating protects only while it is perfectly intact — and a scratch in tinplate makes rusting faster than bare steel would, because the exposed iron becomes a small anode connected to a large cathode. Same idea of a protective metal layer, opposite electrochemistry, opposite failure mode.

Stanislas Sorel patented hot-dip galvanising in France in 1837 and borrowed the name from Luigi Galvani, whose twitching frog legs had given the word galvanic to electrochemistry. Zinc's other outlets follow at a distance: die-cast components, brass, and zinc oxide, which is both the activator that makes sulfur vulcanisation of rubber work at a practical rate and a broad-spectrum mineral sunscreen filter covering the long-wave ultraviolet that many organic filters handle poorly.

The coin that was mostly zinc, and then stopped

The United States one-cent coin has been 97.5% zinc with a thin copper plating since 1982, when rising copper prices made a solid bronze cent worth more as metal than as money.

The substitution bought four decades and then failed on the other side of the ledger. Production costs rose to somewhere between about 1.4 and 3.7 cents per coin, and the Mint struck the final circulating cent at Philadelphia on 12 November 2025, ending a 232-year run. Something like three hundred billion of them remain legal tender, which is a substantial quantity of zinc in jars.

Redox-inert, and that is exactly the point

Around a tenth of the proteins encoded by the human genome bind zinc — several thousand of them. That is a remarkable share for a trace element, and the reason is a negative property.

Iron and copper are useful in biology because they change oxidation state readily, which is also what makes them dangerous: loose iron and copper generate destructive radicals. Zinc has one accessible oxidation state and does no redox chemistry at all. What it offers instead is a strong, geometrically flexible Lewis acid centre that can polarise a water molecule or hold a protein fold rigid, with no free-radical risk whatsoever.

Both uses are everywhere. Zinc finger motifs — small domains folded around a zinc ion — are the most common DNA-binding structure in the human genome, and the protein family they define is the largest one we have. Carbonic anhydrase, which interconverts carbon dioxide and bicarbonate in blood at up to a million reactions per second, is among the fastest enzymes known and does it with a single zinc ion activating a water molecule.

Deficiency was not recognised as a human problem until Ananda Prasad described a syndrome of stunted growth and delayed development in Iranian and Egyptian patients in the early 1960s. It is now understood to be widespread wherever diets are dominated by unleavened wholegrain cereals, whose phytate binds zinc and blocks its absorption. Zinc supplementation is a standard World Health Organization recommendation for childhood diarrhoea, where it measurably shortens episodes.

Reading a diet from tooth enamel

Zinc has five stable isotopes, and the ratio of zinc-66 to zinc-64 in an animal's tissues declines predictably as you move up a food chain — a herbivore's bones and teeth are isotopically heavier than a carnivore's that ate them.

This has become valuable in palaeontology for a specific reason. The standard method for reconstructing ancient diets uses nitrogen and carbon isotopes in bone collagen, and collagen is a protein that rarely survives beyond fifty thousand years or so, and much less in warm climates. Zinc sits in the mineral phase of tooth enamel, which is far more durable. Enamel zinc ratios have consequently opened dietary reconstruction on fossils and in environments where collagen disappeared long ago.