Investigation of Fogging on Glass Display Cases at the Royal Ontario Museum

ABSTRACT

Shortly after a major renovation at the Royal Ontario Museum, it was noticed that the glass panels in many of the new display cases exhibited fogging or hazing on the surface, sometimes in very specific patterns. Cleaning removed the fogging temporarily, but it began to reappear within 12 months. An investigation of fogged glass panels in display cases was undertaken to understand the source of the fogging and to develop an appropriate cleaning method. This included the analysis of residues from glass panels in several galleries, and surface imaging and compositional analysis of glass panels. The fogging residues on the glass panels consist mainly of sodium salts of organic acids and inorganic anions. Sources of the sodium in the residues include air particulate matter and the glass itself. The organic acids and inorganic anions that form salts with the sodium cations likely originate from volatile organic compounds (VOCs) and particulate matter in the air. Examination of the fogging patterns on the glass panels revealed that the sodium salts grow on marks made during cleaning attempts and the manufacturing process. These cleaning and manufacturing marks contain greasy residues that encourage crystal growth. Because of the variation in surface cleanliness, panels with more cleaning and manufacturing residues appear to be heavily fogged while those with less may appear to be unfogged in the museum display cases. A cleaning protocol was tested on two of the glass panels, and was found to remove all traces of grease and fogging residue.