Curated Silver

Coins in the milk, and the man who turned blue

Ask an older relative and you may hear it: Grandma used to drop a silver coin into the milk jug to stop it going sour. Versions of the tale turn up everywhere. American pioneers were said to put silver dollars in their milk churns and water barrels on the wagon trail. Wealthy households preferred silver cups for babies. The phrase "born with a silver spoon in your mouth" may even carry a faint echo of the idea that silver kept a child healthy, though it is mostly about money.

It sounds like a charming old wives' tale. The surprise is that there is real science underneath it. In 1893 the Swiss botanist Carl von Nägeli noticed that tiny traces of metals such as silver and copper were lethal to algae and microbes. He named it the oligodynamic effect, from the Greek for "small power". Silver ions slowly released from a clean surface damage bacterial cells, so a coin in the milk may genuinely have slowed spoilage, if only a little.

People had sensed this long before anyone could explain it. The Greek historian Herodotus records that the Persian king Cyrus the Great travelled with drinking water boiled and carried in silver vessels. In 1881 a German obstetrician, Carl Credé, began putting drops of silver nitrate into newborns' eyes to prevent blindness from infection, and the practice spread around the world. Before penicillin arrived in the 1930s and 1940s, silver solutions were a mainstream medicine. Today silver still lines wound dressings, catheters and some water filters.

But silver has a strange side effect. Swallow too much of it, for too long, and it lodges in the skin, where light darkens it. The result is argyria: a permanent slate-blue or grey tint.

Its most famous case was Paul Karason, from Washington State. In the 1990s he began drinking homemade colloidal silver and rubbing a silver salve on his face for dermatitis, sinus trouble and acid reflux. Over the following years his fair, freckled skin turned a deep purplish blue. When he appeared on American television in 2008, he became an overnight curiosity, nicknamed the real-life "Papa Smurf". He kept drinking it, saying it had helped his ailments, and remarked that what mattered was character, not colour. He died in 2013.

So the folk wisdom was half right. Silver really does fight germs, as the coin in the jug suggested. It just does its best work outside the body, not in it.

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