Benjamin Franklin understood something fundamental about money that still shapes modern economies: Money only works when people believe it is real.

In the early 18th century, the British colonies suffered from a chronic shortage of gold and silver coins, forcing local governments to rely on paper bills for trade and everyday commerce. But paper currency created a dangerous new problem: Unlike metallic coins, paper money could be easily copied, altered and faked.

Long before his experiments with electricity or his role in the American founding now 250 years ago, Franklin spent years working with paper, ink and printing. In the process, he developed a practical understanding of materials and manufacturing.

Nearly three centuries later, modern scientific analysis reveals how sophisticated some of his anti-counterfeiting strategies were. My colleagues and I in materials science recently analyzed hundreds of surviving colonial American bills, including notes printed by Franklin.

Using modern imaging and scientific methods, we examined fibers, pigments and microscopic structures hidden in the paper. The results suggested that Franklin approached currency as a practical materials problem.

Printing money that people could trust

Although paper money originated in China more than a thousand years ago, it did not appear in Europe until the 17th century. By the early 18th century, the American colonies lacked enough gold and silver coins to support a growing economy. To keep commerce moving, many colonies began issuing paper money instead. But paper currency also created anxiety because the colonial bills were relatively easy to fake.

Forged notes circulated widely. Printers even put variations of the phrase “To Counterfeit Is Death” on colonial money and detailed harsh punishments for........

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