Archaeometric studies on the deterioration of glass artefacts of Su Terazisi and Kral Kızı regions in Enez (Ainos) excavation

The subject of this study is the determination of the chemical content of 31 glass finds in the ancient city of Enez (Ainos) located in the district of Enez in the province of Edirne, and archeometric investigations on the association of chemical contents with the layers of deterioration in the samples. The physical condition of glass finds was firstly examined, the layers of deterioration on the glass surface were documented with photographs, their thickness was measured with a digital thickness meter, their colors were identified by chromameter, and images of the bubbles and deterioration products were taken under an optical microscope. The deterioration existing on the surface of the glass was visually examined, and a table was created by determining the existing types of deterioration and their degree of deterioration. The aim of this study is to investigate the chemical contents of the Enez archaeological glass, and the chemical changes that occur during the deterioration process with the hope that the results will contribute to the studies on this subject. Polarized Energy Dispersive-X-Ray Fluorescence (PED-XRF), Scanning Electron Microscope-Energy Dispersive Spectrometry (SEM-EDS), and Raman (Confocal) Spectroscopy methods were used to determine the element and mineralogical contents of the glass samples. According to the results of the analysis, when the contents of silicon-calcium-sodium were evaluated, the glass samples were found to be typical soda-lime-silica glass. Natron or trona was used as flux in the production of glass. Strontium (Sr) and zirconium (Zr) contents of the samples suggest that sea sand is used as the source of silica in production. The visible colors of the samples were determined by chromametric analysis and these results were later supported by PED-XRF analysis. The colorants are iron (Fe), copper (Cu), cobalt (Co) and lead (Pb). After the 1st Millennium AD, large workshops of important regions with prominent glass compositions emerged. We can divide Enez glasses into 4 different groups according to several main glass groups determined according to PED-XRF analysis results on 10 samples; Roman manganese-decolorized glass, Roman mixed antimony and manganese glass, HIMT (High Iron, Manganese and Titanium) glass, and Levantine I. When the deterioration layers of the samples belonging to the Roman Period are examined visually and with an optical microscope; types of deterioration resulting from the chemical composition of glass, such as iridescence, dulling, milky or enamel-like weathering (black discoloration), pitting, and ploughing have been identified. The high amount of SiO2 found as a network former in the batch increases the mechanical resistance of the glass. The reason for the SiO2 content that is lower than expected is the deterioration in the glasses. Glass can undergo chemical reactions in time, due to contact with water and/or humidity within air. Those reactions are highly dependent on the glass composition, its production temperature in kiln and firing duration, pH and temperature of the medium around glass. The gel layer originally formed on the glass surface is rich in silicon, and poor in sodium and calcium. The high content of SiO2 in the deterioration layers supports the deterioration in the glasses. It is expected that the amount of flux agent (Na2O) and stabilizer (CaO) in the gel layer of the surface to decrease caused by glass objects contacting with moisture and/or water. However, the high amount of Na2O and CaO in the results of SEM-EDS analysis of the samples is thought to be due to the accumulation caused by the marine effect as a result of the ancient city being very close to sea. Enamel-like weathering (black discoloration) is characterized by manganese content. Along with the high manganese content, iron content is expected to be high. In the black discoloration in the enamel-like weathering, high manganese content is observed, while the same element is always less common in the overall structure of the glass and other types of deterioration. As manganese and iron stand out in black crust type deterioration products through Micro XRF, PED-XRF, and SEM-EDS analysis of glass samples, the presence of manganese and iron contents determined by Raman analysis supports these results. As a result of the Raman analysis, the content of SiO2 and Fe in the gel layer and manganese and iron content in the layers seen in black discoloration (enamel-like weathering) as well as pigment content that can support the color of the bluish-green color sample has been revealed.