Magazine|How to Clean Paper Currency
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By Malia Wollan
“No one wants soiled or limp bank notes,” says Peter Balke, a senior policy adviser for De Nederlandsche Bank, the central bank of the Netherlands. Balke’s work has nothing to do with money laundering, which is the bailiwick of law enforcement; for much of the last decade, he has studied how cash gets dirty and methods for keeping it cleaner. Globally, governments spend nearly $10 billion annually replacing grimy or crumpled cash (some half a billion euros are shredded each month for this reason). After Balke published research finding that people’s waxy skin oils are mainly to blame, he and his colleagues began investigating what could be done about it. “To clean money,” he says, “you need to remove that built-up sebum.”
“Bleach bank notes in the sun,” Balke says. One scientist has suggested letting ultraviolet light do the work by laying out the cash on the central bank’s roof. (“We’d rather keep it in the vault,” Balke says.) Most bills will remain intact in the washer and dryer. But while a wash cycle may make your money look untainted, it nonetheless ruins the bills; hot water can damage security features, and detergents change the way cash reflects light, which currency-sorting machines detect. Banks shred washed money.
At the microscopic level, because cash is so highly trafficked, it becomes a sort of palimpsest that records all the hands and back pockets and piggy banks it has passed through, accreting a kind of monetary microbiome. A study of $1 bills in New York identified a total of 397 bacterial species. Swiss researchers discovered that when they smeared bills with mucus from children with the flu, the virus lived for up to 12 days. Bank notes also retain evidence of our recreational habits. Ninety-five percent of the currency researchers tested from Washington showed traces of cocaine; in Macao, 98 percent contained ketamine.
There is a cleaning technique that works without damaging your dollars. It requires highly pressurized and heated carbon dioxide. “You basically dry-clean it,” Balke says. After studying the method, the European Central Bank opted to use a sebum-repelling varnish on euros instead. Despite dozens of online tutorials on how to clean cash at home, Balke doesn’t think you should bother: If you end up with a particularly nasty (or mangled) bill, most banks will let you exchange it.
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A version of this article appears in print on , Page
27
of the Sunday Magazine
with the headline:
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