How Benjamin Franklin laid groundwork for the U.S. dollar by foiling early counterfeiters

SAN FRANCISCO — We know Benjamin Franklin as an inventor, publisher, scientist, diplomat, and U.S. founding father. Now a university research team has shed new new light on his anti-counterfeiting designs for colonial currency.

Franklin was an early innovator of printing techniques that used colored threads, watermarks, and imprints of natural objects such as leaves to thwart unauthorized knockoffs of his paper bills.

A team at the University of Notre Dame has used advanced scanning techniques that reveal some of Franklin’s methods in greater detail.

The new research, published Monday in the Proceedings of the National Academy of Sciences, describes data gathered with techniques such as spectroscopy and fluorescence tests, which use light to identify elements such as carbon, calcium, and potassium in test samples.

Researchers also used electron microscopes for imaging fine details.

The intent, said lead author Khachatur Manukyan, a Notre Dame associate professor of physics, was to learn more about the materials used by Franklin and his network of affiliated printers and how those distinguished their bills from cheaper copies.

“The goal was to decode what type of material they used,” Manukyan said in an interview. “And then we found some very interesting differences between this money and other printers.”

The researchers examined Franklin’s penchant for including watermarks, tiny indigo-dyed threads, and “fillers” of special crystal in printed bills to create barriers to copycats.

The paper also highlights Franklin’s use of “nature printing,” a technique by which he transferred the detailed vein patterns of tree leaves to printing plates.

The fillers served to strengthen Franklin’s bills and thus extend their life over cheaper paper used by counterfeiters.

The dyed threads added another layer of production difficulty, as did the fine details of nature-printed images, which less skilled printers might not be able to duplicate.

The researchers at Notre Dame also learned that Franklin — whose image appears on the $100 bill — developed a graphite-based ink; other printers were mostly using inks derived from “boneblack,” a charcoal-like substance produced by subjecting animal bones to high temperatures in a kiln that limited the flow of oxygen.

The Revolutionary War brought on such a surge of counterfeiting — much of it, apparently, by the British Army — that the subsequent U.S. government shunned paper bills for decades in favor of coins.

It was not until the onset of the Civil War in 1861 that the federal government authorized the printing of dollar bills called “greenbacks.”

Among the features in those U.S. banknotes were, unsurprisingly, colored threads. These remain in use in a modernized form.

U.S. currency today features an embedded “security thread” in bills of $5 or more that is a thin vertical band that fluoresces under ultraviolet light.