An investigation on the patina of ancient bronze coins

The patina of ancient bronze coins of different historical periods (from VI cent. A.D. to X cent. A.D.) coming from different Mediterranean countries was investigated with different surface physical analyses. X-ray photoelectron spectroscopy measurements were performed by using electron emission induced by 1.4keV X-rays. Laser ablation coupled to mass quadrupole spectrometry analyses were developed by using a pulsed Nd:YAG laser operating at 532nm, 3ns pulse width, 30mJ pulse energy and 10Hz repetition rate, coupled to a mass quadrupole spectrometer with a mass range of 1-300amu. Laser ablation induces controllable surface layers removal in high vacuum. At present, the mass spectrometer detects chemical elements and compounds. This work, more than to solve a numismatic question, has been carried out in order to test the validity of the above experimental techniques in view to further analyse the same coins, based on better quality statistics. Preliminary results presented in this paper indicate significant differences in the chemistry of the coins patina.