The Royal Ontario Museum is a large institution, with a mixed collection of around six million natural history specimens and art and archaeology artefacts. Along with expected problems due to carbonyl pollutants, such as calcium acetate efflorescence on calcareous fossils stored in birch and oak cabinets, and calclacite and Efflorescence X on ceramics stored in similar conditions, there is one particular mystery which is currently under investigation as a possible carbonyl pollutant problem.
Over the last few years, a hazy deposit has appeared on the inside of case vitrines in some of the newer galleries, constructed between 3 and 10 years ago. The deposit is particularly visible when viewed by raking light, and in some instances seems to concentrate around marks which appear to have been left by sticky tape. The visual effect is compounded by deposits left on the exterior of vitrines due to poor cleaning.
Initial possible sources of the problem included case construction materials, paints or fabrics, cleaning substances, and contaminants from the humidity control devices. Cleaning fluids were ruled out, since they are used on the outside of the vitrines and the deposit appears on the inside. Local climate control can also be eliminated, since a survey of affected cases shows that the deposit appears equally in cases glazed with both glass and Plexiglas; with humidity control by silica gel, micro-climate generators, or larger humidity control units; with a positive pressure flow (designed specifically to remove pollutants from construction materials) but no control of humidity; or without climate control of any form. As for construction materials, as far as possible, all wood products, paints, other surface finishes etc., for recent galleries have passed the Oddy Test.
Samples of the bloom were taken from one of the more seriously affected cases in the European gallery. Under the microscope the substance appears powdery or crystalline rather than oily, as had been expected. Though it appears to be water soluble in at least one display case. Removing the deposit from the vitrines requires significant effort, and it does clump and streak in a greasy fashion.
The source of the bloom does need to be identified. If indeed it is the product of one of the materials used in case construction, then the more galleries and exhibits for which we use that product, the more we compound the problem.
However, at this point in time, though final analysis results have not yet been received, XRD and XRF analyses seem to indicate that the deposit may be calcium and / or sodium chloride. This possibility is supported by an analysis of general museum dust collected from computer screens, which shows similar components. Further evidence comes from the Geochronology department, which has been experiencing failure of their electronic equipment due to shorting out.
The likely answer to the problem, therefore, is that the deposit in the display cases originates in the buildings air conditioning system and is not, in fact a result of carbonyl off-gassing. The HVAC system uses reverse osmosis, and has in the past had problems with chloride ions passing through the membrane. Since the humidification for the air conditioning has recently been upgraded, we can hope that a thorough cleaning of the case vitrines will remove the problem, and that it will not recur.
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© April 25th, 2000