Among collectors of Continental Currency, it is common knowledge that Benjamin Franklin was prodigious in his output as a printer of paper money, beginning as early as 1731 when Pennsylvania gave him a contract to print £40,000 worth of currency.

Ever the inventor, he was also at the forefront in seeking ways to thwart the epidemic of counterfeiting. Most famously, he used leaves to make copper plates, on the theory that a counterfeiter would have difficulty replicating the pattern of veins on a leaf.

A study published to widespread media coverage on July 17 in the Proceedings of the National Academy of Sciences claims to shed new light on his experimentations with papers and inks. A research team at the University of Notre Dame led by Dr. Khachatur Manukyan, an associate research professor in the Department of Physics and Astronomy, spent seven years using techniques such as infrared, electron energy loss spectroscopy, and X-ray analysis, to study close to 600 notes from Franklin and some of his contemporaries in the university’s collection. They also looked at counterfeits. The technology used may be new, but many of the “findings” have been known to students of Colonial Currency for years.

Secure paper money was important to the colonies because gold and silver coins did not stay there for long, as it was used to pay for imports. Franklin realized, Dr. Manukyan said, that to sustain paper money’s viability, it “had to stay a step ahead of counterfeiters. … But the ledger where we know he recorded these printing decisions and methods has been lost to history. Using the techniques of physics, we have been able to restore, in part, some of what that record would have shown.”

They used five university research entities, the Nuclear Science Laboratory, the Center for Environmental Science and Technology, the Integrated Imaging Facility, the Materials Characterization Facility, and the Molecular Structure Facility.

They researched the chemical elements in each item in the university collection and found that the counterfeits have noticeably high quantities of calcium and phosphorus, elements that were found only in traces in genuine notes. Also, the pigments Franklin used were distinct.

As reported in a synopsis of the research released by the university, “Although Franklin used (and sold) ‘lamp black,’ a pigment created by burning vegetable oils, for most printing, Franklin’s printed currency used a special black dye made from graphite found in rock. This pigment is also different from the “bone black” made from burned bone, which was favored both by counterfeiters and by those outside Franklin’s network of printing houses.”

Franklin was also innovative when it came to paper. It had long been thought that the addition of small colored fibers to paper pulp was invented in 1844 by Zenas Marshall Crane, son of the founder of Crane Paper. Dr. Manukyan and his colleagues discovered evidence that Franklin was including colored silks in his paper decades earlier. This is not actually revelatory. It is first mentioned in Eric P. Newman’s Early Paper Money of America on page 327 (2023 edition), referring to the issues of March 20, 1773.

The team also found that notes printed by Franklin’s printing network have a distinctive look because of the addition of a translucent material called “muscovite,” a light-colored mica. This is also referenced in Newman.

The team speculates that Franklin initially began adding the muscovite to his papers to make the printed notes more durable, increasing the size of the crystals over time, and that he continued to add it when it proved to be a helpful counterfeit deterrent.

The team was aware of the importance of nondestructive research techniques and recognized that there were physicists who would be turned off by such restrictions. “We were fortunate to have student researchers on this project with interests both in physics as well as in history and art conservation, Malukyan said, “and the core research facilities as well as the Rare Books and Special Collections team were incredible research partners. Without an uncommon level of collaboration across disciplines, our discoveries would not have been possible.”

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