The development of growth rings on ancient glass surfaces: Description and simulation of the weathering

Abstract

The present work investigates the weathering process of glass surfaces with the formation of corrosion growth rings investigated by X-ray photoelectron spectroscopy, optical microscope, environmental scanning electron microscope and particle induced X-ray emission. The analysed samples are both ancient and recent glasses. The first set of samples is constituted by Roman glass fragments originally belonging to the load of the Iulia Felix ship, sunken in the Northern Adriatic sea (Grado, Italy) during II century AD. The samples were already investigated in the past [F. Barbana, R. Bertoncello, L. Milanese, C. Sada, J. Non-Cryst. Solids 337 (2) (2004) 136; B. Dal Bianco, R. Bertoncello, L. Milanese, S. Barison, J. Non-Cryst. Solids 343 (2004) 91; B. Dal Bianco, R. Bertoncello, L. Milanese, S. Barison, Surface Eng. 21 (5–6) (2005) 393; B. Dal Bianco, R. Bertoncello, L. Milanese, S. Barison, Archaeometry 47 (2) (2005) 353], but their production process is still unknown. The second set of samples belongs to the stained window of S. Giovanni church in Polegge (Vicenza, Italy) and it is dated to 1930 ca. The glass production process is well known. In fact, every tessera is made of soda-lime glass. On one side only, the glass is coated with a green pigment (low melting temperature glass) and then heated in oven in order to fix it on the glass. The window is then mounted and fixed to the wall. Unfortunately, during this procedure, the window was positioned inside-out, so that the painted surface was exposed to the direct action of the atmospheric conditions. This anomaly favoured the fast degradation of the tessera, with the presence of concentric rings at the surface. Another set of samples was produced in order to simulate the effects of moisture at the glass surface, using an industrial soda-lime glass and coating it with a painting originally used in 1930s. The comparisons between the corrosion of the three sets of samples suggest that the Iulia Felix glasses could have been prepared with the same technique.