Pollutants can be generated both and outside and inside buildings. Many pollutants known to cause human health problems can also cause damage in collections. The two general types of pollutants that contribute to the deterioration of museum collections are particulates and gasses. 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 or exhibit materials. These will cause chemical deterioration such as corrosion, yellowing and embrittlement.
- Abrasive particulates such as soot, dirt and dust. Dust often has a large organic component, consisting of vegetable matter, skin and hair, which together are an excellent food source for pests. Furthermore, these can be abrasive and disfiguring, and absorb moisture from the surrounding atmosphere.
Contaminants more commonly deposited via direct contact with artifacts include oils and salts from skin transferred during handling, and heavy metals such as arsenic that were used historically as pesticides on some types of museum collections.
Particulate pollutants, either gaseous or deposited by physical contact can become concentrated or trapped close to the object’s surface. Over time dust can integrate with the surface of porous artifacts. As the pores expand and contract with temperature and relative humidity changes, dust can become adhered to finishes or surface coatings that soften at warm temperatures.
Sources of pollutants in historic homes and museums include:
- Dust from fibrous materials - i.e. carpeting and clothing
- Hair, skin and finger nail sheddings
- Kitchen cooking
- Oil-burning furnaces and/or fireplaces
- Newly applied oil-base paints
- Sulphur from rubber products; wool; felt; industrial emissions (pulp and paper mills); burning of fossil fuels
- Chlorides from sea air
The most effective way to avoid damage from pollutants is to prevent their deposition. The following initiatives will help to eliminate air pollutants:
- Maintain a clean environment.
- Place appropriate filters on fresh air intake for HVAC systems.
- Ensure that windows are not opened in areas with collections
- Repair broken glass, dried putty and caulking in windows and doors to eliminate cracks, which admit dirt.
- Install weather stripping on windows and doors.
- Confine smoking and eating to areas, which do not contain artefacts, or restrict from building. Preferably vent these areas separately.
- Paint or cover concrete floors to prevent abrasive dust from settling on artefacts.
- When preparing artefacts for exhibit or storage, use recommended construction and mounting materials which do not emit pollutants and/or use well seasoned materials and finishes whenever possible.
- Use enclosures for artefacts on storage and display wherever possible.
When necessary, products with activated carbon, zeolites, or potassium permanganate will help capture gaseous pollutants in enclosed spaces.
Sources of Information:
Hatchfield, Pamela, 2002. Pollutants in the Museum Environment. London: Archetype Publications.
National Park Service – Exhibition Conservation Guidelines CD-ROM. For more information see: http://www.nps.gov/hfc/products/cons/ex-con-guidelines.htm