Thank you, Winesteven! This article appeared in the Wall Street Journal - paywalled, so I kept looking. It's based on an article in the Proceedings of the National Academy of Science - also paywalled. But I did find this one that's a bit easier on the eyes:
How Benjamin Franklin fought money counterfeiters
Blue threads and muscovite, a reflective mineral, were incorporated into paper bills
https://www.sciencenews.org/article...ounterfeiter
How Benjamin Franklin fought money counterfeiters
Blue threads and muscovite, a reflective mineral, were incorporated into paper bills
https://www.sciencenews.org/article...ounterfeiter
Inordinately fascinated by bits of metal with strange markings and figures






















