Those results show that the role played by dry deposition, even if less important than that of the wet deposition, cannot be neglected.

An amalgam mirror is a mirror type, used from the fifteenth century until the end of the nineteenth century, where the reflective layer is constituted by a tin amalgam layer adhered to a glass sheet. In this work, two amalgam mirrors samples were studied by scanning electron microscopy with an energy dispersive spectrometer and by micro-X-ray fluorescence elemental mapping to go deeply into the understanding of the degradation mechanism of the amalgam layer of ancient mirrors. The investigation has been focused for the first time on the reflective surface of the amalgam layer adherent to the glass sheet to better understand the processes of amalgam corrosion. The two amalgam degradation compounds, romarchite and cassiterite, has been spatially differentiated by scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) maps. SEM images and micro-X-ray fluorescence and EDS maps showed that the amalgam degradation products grow up to form hemispherical stratified calottes. This structure is probably due to a mechanism involves cyclic phases and oxygen radial diffusion from a superficial oxidation nucleus.

In a previous paper the weathering of the internal surface of empty glass containers before filling was investigated. Several phenomena were identified and described such as leaching of modifiers, formation of a hydrated leached layer and of crystalline deposits mainly consisting of Ca-carbonates and Na-carbonates. Localised glass surface corrosion was sometimes also detected. The role of the storage conditions, time, temperature, relative humidity and concentrations of pollutant gases (CO2, SO2), in the weathering phenomena was highlighted [1]. In the present work the composition of the weathered glass layer and the nature of the crystalline deposits are investigated. Furthermore, in order to examine more closely the weathering mechanisms and their causes, the correlation between durability laboratory tests and chemical composition of soda-lime-silica glass are discussed.

No abstract

When a glass is exposed to the atmosphere the combined action of water and environmental elements leads to the weathering of the glass surface. Both the chemical composition of the glass and the environmental parameters influence the mechanism of glass weathering mainly consisting in the formation of a layer of hydrated leached glass and salt deposits. The study of these phenomena is very important for both industrial and cultural heritage applications. In order to study the weathering mechanism of glasses exposed outdoor the chemical composition of the glass and the chemical and mineralogical nature of the reaction products should be determined. X-ray micro-analytical techniques such as scanning electron microscopy and X-ray microanalysis (SEM-EDS) and electron probe microanalysis (WD-EPMA) are traditionally employed in this type of investigation. Nevertheless particular compounds are hardly detected with this technique (for ex. nitrates) and no direct information can be obtained on the mineralogical features of the reaction products. Moreover, X-ray diffractometry (XRD) cannot be successfully used because of the very low amounts of deposited material. This work reports the results of a combined complementary X-ray fluorescence spectrometry (WD-XRF), SEM-EDS, WD-EPMA and µ-Raman spectroscopy (MRS) investigation on the surfaces of an industrial float glass and a glass reproducing the low-durable glass of ancient stained windows exposed sheltered outdoor for 6 months. The investigation enabled the identification and characterisation of different reaction products (soluble salts) confirming the need of this analytical approach for the study of the glass weathering process.