Weeping Glass: The Identification of Ionic Species on the Surface of Vessel Glass Using Ion Chromatography

Aqueous films on the surface of unstable vessel glass were analysed. Five cation and eight anion species from eleven glass items in the Rijksmuseum, Amsterdam, the Hamburg Museum and the Corning Museum of Glass have been quantified by ion chromatography. Sodium, potassium, magnesium and calcium cations and acetate, formate, chloride, nitrate, carbonate and sulfate anions are deemed most significant. The results indicate that the compositions of moist films on weeping glass are more complex than generally recognised. The findings are discussed in relation to the sources of the ions and the implications of their diversity for the choice of a suitable relative humidity (RH) for display and storage of unstable vessel glass. The compounds which may form have deliquescence RH values which span the range 11-99%, demonstrating the difficulty of making
recommendations about storage RH to prevent the onset of weeping.