Drying the Tears of ‘Weeping’ Glass—The Coburg Magnesium Chloride Experience

A relative humidity (RH) of 30–40% was considered optimal for the ‘sick’ glasses of the Veste Coburg Art Collections to prevent further corrosion at higher humidity values and crizzling on drying of the gel layer at lower levels. This has been achieved since 1993 by using saturated solutions of magnesium chloride in display cases, providing a constant humidity of 33%. These solutions also absorb volatile harmful ‘carbonyl’ and other pollutants. A visual survey of the glasses and recent ion chromatographic measurements of alkalis on their surfaces confirmed their stable condition after three decades: no crystals, no new haze, no tears, no fragmentation, and no further growth of crizzling.