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:
- Acidic gasses and ozone from the environment
- Organic and corrosive acids such as sulfur dioxide, nitrogen oxides, formaldehyde, etc. emitted by inappropriate storage, exhibit, or packing materials
- Abrasive particulates such as soot and dust
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 well-sealed 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:
- Oils and salts from skin transferred during handling
- Heavy metals (such as arsenical salts or soaps) that were used historically as pesticides on museum collections
Download information about the selection of appropriate gloves for different materials.
By far the most common and problematic contaminant for most collections is dust that builds up in storage and exhibit areas without proper housekeeping. Dust can be abrasive and attract pests, and removing it can cause damage to fragile collections. Well-sealed cabinetry greatly reduces this problem, but can create other problems if components of the cabinetry or the storage materials contained inside off-gas harmful pollutants themselves.
Tips to reduce dust and grime
- Make sure circulating air in the collection is as clean as possible by using filters on your A/C or HVAC system and making sure that they are changed regularly
- Keep windows closed in storage areas
- Keep specimen cabinet doors closed
- Use dust covers on open shelving
Organic Collections: Zoology, Botany, and Material Culture
Dust and dirt can permanently disfigure vertebrate zoology specimens and material culture constructed from animal materials. Care should be taken to prevent the deposition of dust by using closed cabinets and appropriate storage materials.
The shells of freshwater and marine invertebrates 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 collections. High relative humidity accelerates this reaction. To prevent this, inert materials should be used for long-term storage of collections.
Inorganic Collections: Paleontology, Geology, and Material Culture
In addition to the pollutants mentioned above, contaminants impacting inorganic collections can come in the form of chemicals used in the preparation of fossil specimens or the cleaning of stone or ceramic objects (e.g., acids or salts not rinsed away); or as other materials introduced in treatment such as adhesives and consolidants.
Pyritic minerals and fossils can also be a source of contaminants in collections. Pyrite is often found in sedimentary rock, and if exposed to conditions of high humidity, a destructive reaction can sometimes occur. So-called pyrite "disease" involves the oxidation of pyrite (iron persulfide, FeS2) to form iron sulphate (FeSO4), which is several times the volume of the original mineral. The resulting crystal growth causes the specimen to fracture and crumble. As this occurs, sulfuric acid is emitted, 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.
The best way to combat this problem is to keep specimens in dry conditions — under 45% RH. Once the damage begins, it is irreversible and specimens must then be kept under 30% RH. While some remedial treatments exist, good storage practices are the most effective route for preservation.
The Getty Conservation Institute website has information on their extensive research into museum pollutants.
Several National Park Service Conserve-O-Grams offer practical tips for dealing with gaseous and particulate pollutants:
- Dust Covers for Open Steel Shelving
- Byne's "Disease:" How to Recognize, Handle and Store Affected Shells and Related Collections
- Volcanic Ash: Cleaning Museum Objects
The following resources provide more information on pyrite disease and the preservation of pyritic objects:
- National Park Service Museum Handbook Part I, Appendix U:Curatorial Care of Paleontological and Geological Collections, Section E (Factors that Contribute to Specimen Deterioration), pages 7 and 8.
- Pyrite Oxidation: Review and Prevention by Akiko Shinya and Lisa Bergwall, a poster presented at the 2007 Society of Vertebrate Paleontology annual meeting
- Pyrite Preservation by Sally Shelton in the Knoxville Gem and Mineral Society KGeMS Volume XXXII, Issue 2 from February 2001 p. 8
- Collins, Chris. 1995. Care and Conservation of Paleontological Material. Boston: Butterworth-Heinemann