Influence of volatile organic compounds (VOCs) in the alteration of historical unstable glasses

Abstract

Historic glasses can be altered in the presence of inorganic pollutants, such as CO 2 , SO 2, or NO 2 , but also, by the volatile organic compounds emitted by the museum cabinets. Among these pollutants, compounds with carbonyl groups such as acetic and formic acids, and formaldehyde are the most common ones.In this work, a study of the interaction of these contaminants with three of the most relevant historical glasses was carried out. These glasses were soda silicate glass, potash silicate glass, and lead crystal glass. Two alteration tests were carried out in these glasses in the presence of water, acetic acid, formic acid, or formaldehyde. In the first test, the alteration induced by the liquid solution was evaluated by the pH monitoring and the study of the ions lixiviated by inductively coupled plasma optical emission spectroscopy. In the second study, the alteration with gaseous contaminants was carried out. The hygroscopic capacity of the glasses was analyzed by gravimetry, the evolution of the glass surface by Fourier transform infrared spectroscopy in attenuated total reflectance mode, and the ions found on the glass surface by ion chromatography. These methods allowed to observe the different degradations that occurred in the three glasses in the presence of different pollutants in aqueous or gaseous environments.

Influence of humidity in the alteration of unstable glasses

“…This behavior confirms that the acid increased the hygroscopicity capacity of glasses because it supplies protons to the medium, which accelerates the ion-exchange reaction (Equation 1). 22,53 Additionally, the alkali ions lixiviated out from the glass structure (Na + , K + ) are, commonly, hygroscopic, so they attract more environmental water, increasing water content on the glass surface and accelerating also the hydration. 19,22 On the last day of the test, the glass surface was observed by OM.…”

“…22,53 Additionally, the alkali ions lixiviated out from the glass structure (Na + , K + ) are, commonly, hygroscopic, so they attract more environmental water, increasing water content on the glass surface and accelerating also the hydration. 19,22 On the last day of the test, the glass surface was observed by OM. Drops and deposits were located on the surface of all the samples.…”

“…This behavior has been observed in previous studies. 22,53 The presence of formate and acetate ions in neutral environments was caused by the existence of residues on the ceramic plates, which serve as a base inside the desiccators. Although it is an unwanted presence, it serves to verify the great reactivity of these acids with unstable glasses and their strong influence on their alteration.…”

“…[16][17][18] These compounds can accelerate the alteration because, when they are dissolved in a surface-adsorbed water layer, they dissociate releasing protons that produce a fast ion exchange with the alkaline ions from the glass. [19][20][21][22][23] These VOCs are related to materials such as wood, silicone, varnish, etc. and they are found in display cabinets and showcases.…”

“…The common main degradation agents are volatile organic compounds (VOCs) such as formaldehyde, acetaldehyde, and organic acids (formic acid and acetic acid) 16–18 . These compounds can accelerate the alteration because, when they are dissolved in a surface‐adsorbed water layer, they dissociate releasing protons that produce a fast ion exchange with the alkaline ions from the glass 19–23 . These VOCs are related to materials such as wood, silicone, varnish, etc.…”