The Influence of Environment in the Alteration of the Stained-Glass Windows in Portuguese Monuments

Abstract

This work presents the results of the exposure of soda-lime, potash-lime and mixed-alkali silicate glasses during ten and twenty months in different Portuguese monuments with historical stained-glass windows to characterize the influence of local environmental conditions. The glass samples were exposed in the Monastery of Batalha (Batalha), the Monastery of Jerónimos (Lisbon), and the Cathedral of Évora (Évora). A set of analytical techniques to assess the physicochemical effects were used, including optical microscopy and Fourier transform infrared spectroscopy. All the samples presented crystalline deposits on their surface; however, their quantity and nature depended on the atmospheric conditions during the days before the collection. Potash-lime silicate glass was the most altered glass in comparison with soda-lime and mixed-alkali silicate glasses. The samples from the Cathedral of Évora showed a high content of dust and salts on their surface but without severe chemical pathologies; however, those samples exposed in the Monastery of Jerónimos and the Monastery of Batalha presented alteration layers due to a high humidity environment.

Impact of solar radiation and environmental temperature on Art Nouveau glass windows

“…Protective glazing is formed by float glasses (soda-lime silicate glass) with a high resistance to environmental alteration [11,12,60], which creates a physical barrier between the historical stained-glass windows and the environmental weather (rain, wind, pollution…). The protective glazing also decreases the amplitude of the temperature along the day, which carries the reduction of the thermal shocks, the risk of condensation, and the dilatation of the window materials [38,[61][62][63][64][65][66].…”

“…Rain and pollution are the environmental factors that contribute most for the glass alteration [4][5][6][7][8][9][10][11][12]; nevertheless, temperature has also a significant role [13][14][15][16][17]. From the physical point of view, solar radiation can induce the movement of the stained-glass windows due to the dilatation of the different materials [14].…”

The Influence of Raw Materials on the Stability of Grisaille Paint Layers

“…Different substrate glasses were produced (Table 1) according to the compositions of the most common glasses from historical stained-glass windows [17]. They were melted in an electric furnace (TERMOLAB-BL) at 1400 • C for 3.5 h in ceramic crucibles and blown into the form of a roundel using the same procedure as the historical production of crown-window glass.…”

“…The composition of the different substrate glasses is shown in Table 3. These glasses represent typical compositions from historical stained-glass windows: soda-lime silicate glass, potash-lime silicate glass, and mixed-alkali glass [17]. The glass slide is also classified as soda-lime silicate glass.…”

Environmental degradation of Modern non-balanced glasses

“…Even, the accumulation of deposits raised the dealkalinized areas that caused their detachment [figure 1 b]. The morphology of the cavity, with conchoidal form, most aggressive ones are rain, wind, pollution, and aerosols (Woisetschläger et al 2000;Munier et al 2002;Melcher and Schreiner 2005;Melcher et al 2008;Gentaz et al 2011;Lombardo et al 2014;Palomar et al 2018;Palomar et al 2019). In an indoor environment, these alteration agents are minimized; however, high environmental humidity and volatile organic compounds (VOCs), mainly the formic acid from the wood of the furniture, can accelerate the alteration mechanism.…”