Micro-chemical surface investigation of brittle carthaginian and roman silver artefacts

Brittle Carthaginian and Roman silver artefacts, such as bracelets, coins, small jewels and cups, were found in extremely brittle condition during archaeological excavations in different Italian archaeological sites. Some of these silver objects are accidentally easily broken with little applied force and with only small deformation. In order to identify the origin of brittleness, fresh fractured surfaces have been investigated by means of the combined use of surface and micro analytical techniques such as X-ray photoelectron spectroscopy, scanning electron microscopy (SEM) and field-emission SEM (FESEM) equipped with an energy dispersive X-ray spectrometer, optical microscopy and X-ray diffraction. The overall experimental findings show that the main external brittleness agents are chloride ions that come from the soil of the excavation sites and attack the silver artefacts along the grain boundaries forming a thin layer or islands of silver chloride.