The team analyzed a copper denarius coin from the Roman Empire, dating to the first century B.C. Once carefully plated in silver, the layer has now worn off, and the patina from the oxidizing copper below has grown over most of the surface. But traces of the handiwork remain in small amounts of mercury that hinted at how the silver was pasted on. This superior plating technique would ensure that the telltale copper didn't show through as the coins were passed from hand to hand.
The altar at the Basilica of St. Ambrogio, dating to A.D. 825, is a wooden case with gold- and silver-plated panels. The researchers found mercury mixed in with the plating, which suggested the liquid metal was used as glue.
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The team also analyzed the ceramic back leg of a statue of a leaping lion, which was wrapped in a thin copper layer and finished off with an extra-fine layer of silver that was just a single micrometer (one thousandth of a millimeter) thick. The statue was left looking like it was solid silver, the authors write, and could have allowed the designers to clear a tidy chunk of money.
—Nidhi Subbaraman, NBC
Gabrial Ingo, Giuseppe Guida, Emma Angelini, Gabriella Di Carlo, Alessio Mezzi and Guiseppina Padeletti are the authors of "Ancient Mercury-Based Plating Methods: Combined Use of Surface Analytical Techniques for the Study of Manufacturing Process and Degradation Phenomena," published in the Accounts of Chemical Research.