Analytical and microstructural aspects related to the production of the follis-type roman coins

The work described here is part of the experimental activities carried out to study the Misurata hoard. Kept in the Archaeological Museum of Leptis Magna (Homs, Libya), the hoard consists of about 108,000 silvered bronze coins of the follis type, minted between A.D. 294 and 333 and is therefore the largest of antiquity. At the present stage the work has mainly concerned a) the microstructural and microanalytical investigation of a follis similar to those of the hoard and b) in situ non-destructive X-ray fluorescence (XRF) analyses of about 250 coins from the hoard. The microstructural investigations, carried out by scanning electron microscope (SEM), were focused on the fabrication technology, with special regard for the silvering technique. Two alternative hypotheses were considered: 1) the silver-rich surface was produced by the silver already contained in the alloy) and 2) the silver layer was someway deposited on the coin surface. Since only a single coin was investigated, we could not provide irrefutable confirmation of any of the two hypotheses. The other experimental activity regards the in situ investigation of the hoard, that was carried out by means of a portable XRF spectrometer; the shortness of the measurements (120 s) allows to investigate a large number of coins and obtain statistically significant data. The count-rates of silver and other elements were traced - not quantitatively analysed - for different mints and types and significant differences were found.