Micro-stratigraphy of Copper-based Archaeological Objects: Description of Degradation Mechanisms by Means of an Integrated Approach

The aim of this paper is to presents preliminary results obtained during a study performed on artifacts made of copper-based alloys in two archaeological sites in Dobrogea, Romania (the two villages of Nufărul and Ibida). An integrated approach makes use of OM, SEM-EDX, XRD, FTIR and RAMAN spectroscopy both on surface and polished cross section and revealed the complex multilayered structure of the alteration layers. INTRODUCTION Degradation of metal artefacts in soil occurs through different processes: chemical, electrochemical and microbiological. As a result, they tend to return to their mineral’s state, as thermodynamically more stable then the metallic state. The way this processes occur is a function of multiple factors that can be classified as endogenous (nature of alloy, technology to obtain the object, its shape and dimension) and exogenous (soil porosity, humidity, conductibility, depth of burial...) [1]. As early as in 1976, a polish chemist, Hanna Jedrzejewska [2], suggested to consider ancient bronzes as “document of the past” and proposed to preserve materials of little or no artistic value for scientific investigations. Since that time, several Authors [3-8] dedicate their scientific interest to the elucidation of the long-term corrosion mechanisms occurring for artifact made of bronze or copper alloys. A comprehensive study realized by Mattsson et.al. [8], focused on the enhancement of degradation observed in the last decades because of the acidification of rains. In particular they tried to establish a correlation between the alteration suffered by bronze artifacts, their actual environment (geology, geography, local or distance from polluting sources) and their archaeological context (type of site, depth of burying), by visually examining the degree of degradation, measuring the weight of the artifact and determining numerous parameters characterizing the objects (chemical-physical data records). The present work intends to give our contribution in the understanding of the mechanisms of degradation by presenting the results obtained during the examination of heavily degraded copper-based artifacts excavated in two archaeological sites located in Dobrogea, Romania. The purpose is to report the occurrence of uncommon alteration products interesting degradation patterns, and to delineate a research project that involves a campaign of analyzes aimed to characterize the soil of the archaeological sites described later in detail. These information could be useful not only to give a better interpretation to the results already obtained, but also for any further investigation undertaken for artifacts excavated from those sites. 1 9th International Conference on NDT of Art, Jerusalem Israel, 25-30 May 2008 For more papers of this publication click: www.ndt.net/search/docs.php3?MainSource=65