Mecanismo de corros？o em numismas de época romana provenientes da Senhora do Castelo

the corrosion products on bronze roman coins of cu-base alloys from senhora do castelo, dated of 4th century, have been characterized by means of optical microscopy (om), scanning electron microscopy combined with energy dispersive spectrometry (sem-eds), energy dispersive x-ray fluorescence (edxrf), and x-ray diffraction (xrd). chemical composition of the coins was also examined. the eds and xrd data show that lead has a high rate of corrosion, which in interaction with the environment is later precipitated as a complex chlorine-phosphate of lead with a yellow-greenish hue (pyromorphite).