Benjamin Franklin, one of the Founding Fathers of the United States, polymath, and renowned inventor, is still featured on the American $100 bill today. However, he is perhaps less well known for the role he played in establishing the pre-Federal American monetary system. In the early 18th century, the supply of gold and silver coins in the American colonies was rapidly running out, drained away to pay for imported manufactured goods. Franklin, who was both a statesman and a printer, saw that the colonies needed a way to produce their own money if they were going to be able to expand the economy and gain financial independence from Britain. The answer, he proposed, was paper money.
Throughout his career, Franklin – who had opened his own printing house in 1728, aged just 23 – went on to print nearly 2.5 million paper notes for the Delaware, New Jersey, and Pennsylvania colonies, and created a network of printers in other colonies, including New York, Maryland, and South Carolina, which he supplied with printing presses, paper, and ink. At this time, paper money was still a fairly new concept and was viewed with some scepticism. Of particular concern were fears that paper money would be a prime target for counterfeiting. To tackle this, Franklin’s notes incorporated several clever security features that made these bills harder to duplicate. The most famous of these was ‘nature printing’, the use of unique images of leaves and other natural subjects that were difficult for forgers to copy, but this was not the only technique used.
The historical ledgers where Franklin recorded details of his printing methods have since been lost, but a new study led by the University of Notre Dame, Indiana, set out to discover what some of these records would have shown. The team spent seven years analysing nearly 600 paper bank notes, dating to between 1709 and 1790, from the Rare Books and Special Collections of Hesburgh Library at the University of Notre Dame. They used a combination of spectroscopic and imaging techniques to study the chemical composition of the paper, fibres, inks, and fillers of the bills produced by Franklin’s printing network, and compared them to those from other printers, and to counterfeit money from the same period, to find out what made Franklin’s bills distinctive.
The results revealed several previously unknown ways of safeguarding against counterfeiting. The first surprising discovery was that the notes produced by Franklin’s printers used a special black dye made from natural graphite pigments, rather than the ‘lamp black’ (made from burning vegetable oils) that he used in most of his other printing, or the ‘bone black’ (made from burned bone) used by many counterfeiters and other printing houses outside Franklin’s network. This suggests that he selected this graphite-based ink specifically for printing bills.
The material on which the money was printed was innovative as well: a durable ‘money paper’, with several characteristics that made it harder to forge. The analysis identified tiny blue fibres in the paper pulp, which are visible as little squiggles on the surface of the bill. The addition of coloured thread into paper pulp is traditionally attributed to paper manufacturer Zenas Marshall Crane in 1844, but it seems that Franklin and his associates were including coloured silks in paper money as early as 1739. The researchers also discovered that the notes had a distinctive appearance due to the addition of muscovite crystals – a type of translucent mineral – in the paper. It seems that the quantity and size of the muscovite particles used increased over time. It has therefore been suggested that perhaps Franklin began adding them to the paper filler because it made the material more hard-wearing, but discovered during these experiments that they had the added benefit of acting as a security feature as well – large muscovite flakes appear on the paper surface and reflect the light when the bill is tilted, making it much harder to duplicate.
The results of this analysis confirm that the notes printed by Franklin and his associates featured a variety of innovations that enhanced their durability and verifiability, and played a key role in the paper money system that developed over the following centuries, and even US currency today. The research has been published in the journal PNAS (https://doi.org/10.1073/pnas.2301856120).
Text: Amy Brunskill / Images: K Manukyan et al. PNAS