When Benjamin Franklin moved to Philadelphia in 1723, he acquired to witness the start of a dangerous new experiment: Pennsylvania had simply begun printing phrases on paper and calling it cash.

The first American paper cash had hit the market in 1690. Metal cash by no means stayed within the 13 colonies lengthy, flowing in a ceaseless stream to England and elsewhere, as cost for imported items. Several colonies started printing bits of paper to face in for cash, stating that inside a sure time interval, they might be used domestically as foreign money. The system labored, however haltingly, the colonies quickly found. Print too many payments, and the cash turned nugatory. And counterfeiters typically discovered the payments straightforward to repeat, devaluing the actual stuff with a flood of fakes.

Franklin, who began his profession as a printer, was an inveterate inventor who would additionally create the lightning rod and bifocals, discovered paper cash fascinating. In 1731, he received the contract to print £40,000 for the colony of Pennsylvania, and he utilized his penchant for innovation to foreign money.

During his printing profession, Franklin produced a stream of baroque, typically stunning cash. He created a copper plate of a sage leaf to print on cash to foil counterfeiters: The intricate sample of veins couldn’t simply be imitated. He influenced numerous different printers and experimented with producing new paper and concocting inks.

Now, in a study published Monday within the Proceedings of the National Academy of Sciences, a staff of physicists has revealed new particulars in regards to the composition of the ink and paper that Franklin used, elevating questions on which of his improvements have been supposed as defenses towards counterfeiting and which have been merely experiments with new printing methods.

The examine attracts on greater than 600 artifacts held by the University of Notre Dame, stated Khachatur Manukyan, a physicist at that establishment and an creator of the brand new paper. He and his colleagues checked out 18th-century American foreign money utilizing Raman spectroscopy, which makes use of a laser beam to establish particular substances like silicon or lead based mostly on their vibration. They additionally used quite a lot of microscopy methods to look at the paper on which the cash was printed.

Some of what they noticed confirms what historians have lengthy recognized: Franklin’s paper cash incorporates flecks of mica, also called muscovite or isinglass. These shiny patches have been most definitely an try to fight counterfeiters, who wouldn’t have had entry to this particular paper, stated Jessica Linker, a professor of American historical past at Northeastern University who research paper cash of this period and was not concerned within the examine. Of course, that didn’t cease them from attempting.

“They come up with very good counterfeits, with mica pasted to the surface,” Dr. Linker stated.

In the brand new examine, the researchers discovered that the mica in payments for various colonies appears to have come from the identical geological supply, suggesting {that a} single mill produced the paper. The Philadelphia space is notable for its schist, a flaky mineral that incorporates mica; it’s attainable that Franklin or printers and papermakers related to him collected the substance used of their paper domestically, Dr. Manukyan stated.

When they examined the black ink on a few of the payments, nevertheless, the scientists have been stunned to search out that it appeared to include graphite. For most printing jobs, Franklin tended to make use of black ink comprised of burned vegetable oils, referred to as lampblack, stated James Green, librarian emeritus of the Library Company of Philadelphia. Graphite would have been onerous to search out, he suspects.

“So Franklin’s use of graphite in money printing is very surprising, and his use on bills printed as early as 1734 is even more surprising,” Mr. Green stated in an e-mail.

Could utilizing graphite ink have been a technique to differentiate actual cash from fakes? Differences in coloration between graphite and lampblack are more likely to have been sufficiently subtle to make {that a} troublesome activity, Mr. Green stated. Instead, we could also be one other instance of Franklin’s creativity.

“It suggests to me that almost from the start he was using his money printing contracts as an opportunity to experiment with an array of new printing techniques,” he stated.

To perceive extra clearly Franklin’s intent, extra analyses of printed paperwork from the period can be useful, stated Joseph Adelman, a professor of historical past at Framingham State University in Massachusetts.

“The comparison I would most like to see would be Franklin’s other publications,” Dr. Adelman stated. “To really test this theory — does Franklin have this separate store of ink?”

In future analysis, Dr. Manukyan hopes to collaborate with students who’ve entry to bigger collections of early American paper cash. These methods may be fairly worthwhile within the examine of historical past, Dr. Linker stated, if scientists and historians can work collectively to establish the very best inquiries to reply.

“I have questions about a whole bunch of inks. There’s a really weird green on some of the New Jersey bills,” she stated, referring to cash printed by a Franklin up to date. “I would love to know what that green ink was made of.”