General information on Pollutants and Collections
The two general types of pollutants that contribute to the deterioration of museum collections are gasses and particulates. These can be airborne or transferred by direct contact. Airborne contaminants may include:
The most effective way to avoid damage from airborne pollutants is to prevent their deposition by having appropriate filters on HVAC systems, ensuring that windows are not opened in collection areas, and using enclosures in storage and displays. When necessary, products with activated carbon, zeolites, or potassium permanganate will help capture gaseous pollutants in enclosed spaces.
Contaminants more commonly transferred via direct contact include:
By far the most common and problematic contaminant for most collections, though, is the dust and dirt that builds up in storage areas without proper housekeeping. Dust can be abrasive and attract pests, and removing it can cause damage to fragile specimens. Well-sealed cabinetry greatly reduces this problem, but can create other problems if the materials of the cabinetry or the storage materials inside off-gas, leading to a build-up of harmful gaseous pollutants.
Tips to reduce dust and grime
Pollutants and Invertebrate Zoology Collections
Freshwater and marine shell collections are susceptible to Byne’s “disease”. This problem occurs when calcium carbonate (CaCO3) reacts with an acidic vapor to form salts. In museum collections, this reaction generally occurs when acidic vapors such as acetic acid and formic acid from wood and wood products used in storage materials are in direct contact with the specimens. High relative humidity speeds this reaction. To combat this, use inert materials for long-term storage of specimens (download the Materials for Storage and Rehousing pdf in the Links & Resources section of this site)
Pollutants and Vertebrate Zoology Collections
Dust and dirt can permanently disfigure vertebrate zoology specimens. Care should be taken to prevent the deposition of dust by using closed cabinets and appropriate storage materials.
Pollutants and Paleontology Collections
In addition to the pollutants mentioned above, contaminants in paleontological collections can also come in the form of chemicals used in the preparation of specimens (e.g., acids or salts not rinsed away after treatment) or materials used in treatment such as adhesives and consolidants. Specimens suffering from pyrite “disease” emit sulfuric acid, which will contaminate storage materials and damage other specimens nearby. Any specimens suffering from pyrite disease should be isolated from the rest of the collection and stored in low relative humidity conditions.
Pollutants and Physical Sciences Collections
Geological specimens may be susceptible to Byne’s disease (see above) and Pyrite “disease”. Pyrite (iron persulfide: FeS2), is often found in sedimentary rock. If these specimens are exposed to conditions of high humidity “pyrite disease” (also known as pyrite “rot” or “decay”) can occur. The mineral oxidizes and forms iron sulphate (FeSO4); this oxidation product is several times the volume of the original mineral and the resulting crystal growth and expansion causes the specimen to fracture and crumble.
The best way to combat this problem is by keeping specimens in dry conditions – under 45% RH. Once the damage begins it is irreversible and specimens should then be kept under 30% RH. While there are some remedial treatments, good storage practices are the most efficient route for preservation. For more on pyrite disease investigate the following resources:
The Getty Conservation Institute website has information on their extensive research into museum pollutants [http://www.getty.edu/conservation/science/pollutants/index.html]
Several National Park Service Conserve-O-Grams offer practical tips on dealing with gaseous and particulate pollutants.