International Journal of Conservation Science (Sep 2012)
A CHARACTERIZATION OF COINS FROM THE NAJRAN HOARD, SAUDI ARABIA, PRIOR TO CONSERVATION
Abstract
This paper presents the results of scientific examinations and analyses carried out on the archaeological coins discovered in Najran, Saudi Arabia. Optical microscopy (OM), scanning electron microscopy (SEM) coupled with energy dispersive spectrometry (EDS) and X-ray diffraction (XRD) were used to investigate morphological corrosion features, to clear the nature of the patina and to analyze the elementary composition. Morphologically, it was revealed that there are reniform, coral reef and dendritic shapes of corrosion products and heterogeneous multicolor patina on the studied coin surfaces. It was proven that those coins were made of a silver-copper alloy and were covered by three superficial corrosion layers. The main composition of the coin corrosion compounds was identified as copper carbonate, copper chloride, copper silicates, silver chlorides and silver sulphide. The proposed corrosion mechanism revealed that those coins were characterized by heavy degradation phenomena, induced by corrosive species and soil contaminants. The corrosion processes led to the depletion of the copper and silver enrichment near the surface, as compared to the core composition. This study provides useful information for the conservation and preservation of the Najran hoard coins.
