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The control of humidity between certain limits is essential to avoid the alteration of historical objects, such as unstable historical glasses. However, the usual limits can be altered due to the presence of volatile organic compounds. This work presents the results of the exposure of soda, potash, and mixed‐alkali silicate glasses to neutral and acidic (formic) atmospheres with ∼30%, ∼70%, and ∼100% relative humidity. The hygroscopic capacity of the glass was analyzed by gravimetry, and the surface alteration was evaluated by infrared spectroscopy, optical microscopy, and ion chromatography. In all glasses, the alteration begins with alkali ions' lixiviation followed by the silica network's hydrolytic attack. The results showed that soda and mixed‐alkali silicate glasses exhibit similar behavior, while the potash‐lime one experienced the fastest degradation due to its composition. Results also confirmed that high humidity increased the alteration rate causing a higher hygroscopicity and reactivity of glasses. Finally, acidic environments promoted the ion‐exchange reaction at high humidity, accelerating the lixiviation of alkaline ions and promoting the diffusion of water into the glass network. [ABSTRACT FROM AUTHOR]

The most frequent cause of glass degradation is environmental moisture, which is adsorbed on its surface forming a hydration layer that induces the rupture of the glass network. This pathology is accelerated by the accumulation of volatile organic compounds (VOCs), like formic acid. Although there is extensive knowledge about their impact, concentrations inside display cases are difficult to reduce efficiently. This study presents the assessment of different materials to reduce the concentration of formic acid to mitigate the degradation produced in unstable glasses. With this objective, copper threads, steel wool, silica gel, and activated carbon were chosen as low-cost materials with good adsorption or reactivity to the VOCs, exposing them in desiccators to an environment of 100% RH and 10 ppm of formic acid. Given that silica gel obtained the best results, its optimization as a sorbent material was evaluated by maintaining, regenerating, or renewing it when exposed next to the same glass. The tests carried out concluded that the hygroscopic capacity of the glasses exposed with silica gel decreased and, therefore, a lower degradation is observed on its surface. In addition, regenerating and renewing weekly the silica gel improved the results. [ABSTRACT FROM AUTHOR]

Crizzling is an alteration pathology of non-equilibrated glasses that can produce a fast surface alteration. The Royal Palace of Madrid and the Technological Museum of Glass (Segovia) preserved pieces with incipient crizzling produced by the Spanish Royal Glass Factory in the first decades of the 19th century. The objective of this study was to assess the environmental conditions in both collections to enhance their preservation conditions and to identify possible pollutants that can accelerate their alteration. Both collections presented suitable thermohygrometric conditions for general collection; however, it was observed that illumination induces humidity fluctuations inside the cabinets. Passive samplers detected a high concentration of formic acid in some locations, mainly related to the presence of wood furniture. In these locations, glass pieces showed a high surface hygroscopicity (pH 8) and a high concentration of K+- and COOH− ions. • The indoor environments of Royal Palace of Madrid and the Technological Museum of Glass were assessed. • The cabinets' illumination induced daily fluctuations of temperature and humidity. • The most aggressive environments were detected inside wooden wardrobes. • Higher was the concentration of formic acid, faster was the alteration of non-equilibrated glasses. [ABSTRACT FROM AUTHOR]

• K 2 O-PbO-(CaO)-SiO 2 glasses were altered in atmospheres enriched in formic acid. • Higher was the concentration of formic acid, faster was the alteration. • The addition of stabilizers to the glass slowed down the alteration rate. • For the same molar concentration, calcium was better stabilizer than lead. George Ravenscroft designed the lead silicate glasses in 17th-century; however, the first pieces produced showed degradation pathologies after few years. This study reproduces one of the glasses produced by George Ravenscroft and analyses its chemical stability in comparison to two other glasses based on the original composition but with the addition of 5 mol % of PbO and CaO, respectively. The three glasses were exposed to an environment of high humidity and different concentrations of formic acid (0, 100 and 300 ppm), which is the main contaminant in display cases and wooden cabinets. The hygroscopic capacity of the glass was analysed by gravimetry, infrared spectroscopy and µ-Raman spectroscopy. The results show that the acidic environment promotes the ion exchange reaction, accelerating the leaching of alkaline ions, which has a great influence on the durability of the glass. The glasses with a higher content of stabilizers presented a greater stability, especially the glass with calcium. [Display omitted] [ABSTRACT FROM AUTHOR]