The colonies initially adopted the bartering system of the Native Americans, trading furs and strings of decorative shells known as wampum, as well as crops and imported manufactured items like nails.
Some of that silver from Spain and Mexico eventually made its way to the early American colonies. When this was discovered in the 17th century, the silver market in Spain crashed and the coins were devalued, with devastating effects on the colonial Spanish economy, per Wiescher. Between 1645-1648, the silver content dropped from 92.5 percent sterling to just 70-80 percent the rest was a copper admixture. Wiescher analyzed 91 silver rials dated between the 16th and 18th centuries, from Mexico and Potosi, Bolivia. The same trick of replacing some of the silver in coins with copper showed up again thousands of years later in Spain's Latin American colonies. This gives you a silver coin with a copper core, capable of passing the bite test. "Then you remove the coin from the mercury bath and heat it up to drive the mercury out," said Wiescher. For instance, throwing a mixed silver/copper coin into liquid mercury will cause the silver to dissolve and flow around the coin. "So the Romans invented a number of interesting technologies in metallurgy to hide ," said Wiescher. This would reveal any attempt to cut corners. Merchants would typically test any coins proffered as payment by biting on them, since they should be able to taste the silver. Their analysis revealed that most of the coins are composed of silver and copper and that sulfur and iron impurities led to corrosion in some of them.
They also used electron spectroscopy to measure the silver content of each coin and how the impurities were distributed. Wiescher and his students combined XRF scaling with PIXE mapping of the coins to test the currency's quality and learn more about the production techniques. The course covers such topics as nondestructive analysis of the paintings of Vermeer and the Archimedes palimpsest tracking the inks used by medieval scribes for illuminated manuscripts whether the Vinland map is real or a forgery (it was recently conclusively shown to be fake) using studies of the Shroud of Turin to discuss uncertainties in carbon dating and reviewing how Luis Alvarez once used cosmic rays to search for hidden chambers in Egyptian pyramids in the 1960s. These include Raman spectrometers, transmission electron microscopes (TEM), a 3MV tandem accelerator, handheld X-ray fluorescence (XRF) scanners, micro-XRF scanners, and X-ray diffractometers, among others. Much of this work was conducted in conjunction with undergraduate students in physics, chemistry, art restoration, history, and anthropology as part of a course Wiescher teaches at Notre Dame on physics-based methods and techniques in art and archaeology. In the process, students can get certified as operators of a broad range of advanced physics-based instruments and techniques. He recently described those efforts at a virtual meeting of the American Physical Society's Division of Nuclear Physics. His work in this area has included collaborations to analyze a rare medieval manuscript and unearth currency fraud and forgery throughout history, most notably in ancient Rome and Colonial America. Michael Wiescher, a nuclear physicist at the University of Notre Dame, wants to change that perception by applying his expertise-and some of his sophisticated imaging hardware-to research that bridges science, history, and culture. Most people associate nuclear physics with the atomic bomb or nuclear power plants, and those associations are often negative.