History of the Metallic Strip in Paper Money

The idea of using metal threads in money to thwart counterfeiters was patented back in 1848 in England. However it was another century before a bank put the idea into practice, and its effectiveness at deterring criminals from copying bills has been mixed.

The International Bank Note Society, or IBNS, says the Bank of England issued the first metal-strip currency in 1948. When held up to the light, the strip left a black line visible in the note. In theory, if criminals managed to alter or duplicate the face of the note, they still couldn't copy the metal threads. However, counterfeiters simply drew a black line in the same place, and most people were fooled.

In 1984 the Bank of England produced a £20 note with broken metal threads, like long dashes, and proclaimed this would be impossible to replicate. Counterfeiters, IBNS says, used super-glue to hold tiny threads of aluminum foil to the bill. This likewise passed muster with most people handling the money.

Governments didn't give up on using security threads after counterfeiters found a workaround. Instead, they improved the system, which sometimes meant switching from metal to plastic. In 1990, PBS reports, the government started using plastic security threads that say, for example "USA 100" in small print on a $100 bill. Counterfeiters can't duplicate the printing, so even if a criminal bleaches and replaces the rest of the bill, the strip shows the true denomination.

The ABC Offices website says the government doesn't rely just on security threads:

• A watermark duplicates the image of the face on the bill when held up to light. If the bill is a $50 but the watermark is Abraham Lincoln, the paper has been bleached.
• A line on the bill lights up under U-V rays. The position of the line varies with each denomination.
• Counterfeit-detector scanners can alert users if the bill lacks the magnetic ink used in printing real money.
• Real bills have tiny microprinting on them at various points, visible under magnifying glass.
  

Counterfeiters can beat these seemingly foolproof methods, IT security expert Bruce Scheier says, even using inkjet printers and copiers. Most people, Scheier says online, don't subject bills to a thorough scrutiny when a customer puts one down and asks for change, so a bill only has to be good enough to fool a passing glance. This may be getting easier, because as paying with plastic becomes more common, fewer people see paper money regularly. On top of that, the government's frequent redesigns of money may leave consumers less sure what an official bill should look like.