A PhD candidate in Australia is chemically analyzing coins from centuries-old sunken ships to determine their origin.
The Western Australian Museum gave University of Western Australian archaeologist Liesel Gentelli access to coins found in four Dutch wrecks from the 16th and 17th centuries, and two early 18th century wrecks from Portugal and the USA.
They all sank off the Western Australian coast before the Swan River Colony was founded in 1829, along with silver dollars that were then often degraded by seawater, erasing their distinguishing marks.
Gentilli says coins minted in Potosí (Bolivia) are known for their high copper content—the mark of an unscrupulous mint. However she found a high gold content in Mexico City silver, which may have led to more careful smelting processes had the Spanish been aware of it.
She treated each coin with a laser to vaporise a tiny part of the surface at more than 8,000 degrees centigrade and analysed the resulting cloud with a mass spectrometer. "The techniques that I use on archaeological artefacts were developed for evidence," Gentilli says. "The damage that I do to a coin is invisible to the naked eye."
After determining the chemical signatures for coins with a known provenance, she is then able to perform the same analysis on damaged coins with no other distinguishing marks. In so doing she has added elemental composition to the museum's database of coins.
So far she has traced coins to four mints in metropolitan Spain, five in Spanish America, one in the Spanish Netherlands, seven in the United Netherlands and five in Germany.
Trace element fingerprinting has already been used in a number of contexts for provenance determination, notably by Kalgoorlie police to identify stolen gold ores.
"My research will allow for further analysis of other metals, or other types of artefacts as a further proof of concept," she says.
"The database I create will be able to be used by other researchers anywhere in the world who are analyzing Spanish silver, to add to or compare their own findings, perhaps identifying silver artefacts."