Agents of deterioration
The 'agents of deterioration' are a conceptual framework developed by the Canadian Conservation Institute (CCI) used to categorise the major causes of change, loss or damage to cultural heritage objects (such as collections held by galleries, libraries, archives and museums).[1] Also referred to as the 'agents of change', the framework was first developed in the late 1980s and early 1990s. The defined agents largely reflect chemical and physical deterioration pathways to which most physical material is subject. They are a major influence on the applied practice of conservation, restoration, and collection management, finding particular use in risk management for cultural heritage collections.
CCI defines ten 'agents': dissociation, fire, incorrect relative humidity, incorrect temperature, light and ultraviolet light, pests, pollutants (or contaminants), physical forces, thieves and vandals (at times referred to as 'criminals'), and water. The number of primary agents has remained the same since the 1994 with the addition of 'custodial neglect' (now termed dissociation), though the scope and names of some categories have been updated over time to reflect new research or thinking.
Each category may be further subcategorised as rare and/or catastrophic (Type 1), sporadic (Type 2), or constant/ongoing (Type 3), particularly when applied to risk assessments. For example, within the category of physical forces, an earthquake may be designated a Type 1 event; a handling accident where an object is dropped as Type 2, and ongoing physical wear from daily handling as Type 3.[2]
Dissociation
Dissociation refers to the loss of information associated with an object, such as provenance or location information, without which the object loses significance or is lost. In earlier versions of the framework this was referred to as 'custodial neglect'.
Fire
Fire directly consumes cultural heritage through burning or by the deposition of smoke and soot on surfaces. Fire suppression systems can also cause damage - e.g. water damage from sprinklers. For example, about 18 million objects were destroyed in the 2018 fire at the National Museum of Brazil.
Incorrect relative humidity
Relative humidity may result in change or damage when it is too high (resulting in mould growth, increased pest activity, metal corrosion or hydrolysis), too low (causing shrinkage or desiccation) or when it fluctuates, causing organic materials to contract and expand. For this reason, museum environments often have humidity control as part the heating, ventilation and cooling (HVAC) system.
Incorrect temperature
Two primary chemical deterioration mechanisms affecting cultural heritage include hydrolysis and oxidation, which can result in chain scission or cross linking. These occur at ambient temperatures to varying degrees (depending on the material); the rate of chemical reactions increases with temperature. Consequently, cool storage (e.g. storage at 10°C, 4°C or below freezing) is often used to slow the deterioration of vulnerable materials such as cellulose nitrate and cellulose acetate film.
Higher temperatures may also cause softening or melting of material with low melting points, such as waxes and some plastics. Some materials become brittle and lower temperatures, increasing the chance of physical damage on handling. On freezing, ice crystals can physically disrupt delicate surfaces such as photographic emulsions.
Light, ultraviolet and infrared
Visible light exposure will fade many colourants. Higher energy ultraviolet light wavelengths can also cause bleaching, yellowing, discolouration and physical weakening of substrates.
Pests
Many insect species feed on organic cultural heritage material - for example, carpet beetles and clothes moths are attracted to protein-based fibres such as wool and silk; silverfish graze on the surface of books and photographs; various species of borers can infest wooden furniture or frames. Insects, birds and rodents may use cultural heritage objects as nesting material, or soil them with excrement. Bird poo can etch the surface of metal outdoor sculpture.
Pollutants
Atmospheric pollutants such as ozone, sulphur dioxide, hydrogen sulphide and nitrogen dioxide cause corrosion, acidification and discolouration of a variety of materials. Indoor pollutants such as formaldehyde and other volatile organic acids cause similar problems, and may be present in carpets, paints and varnishes or in the materials used to construct display cases or storage furniture. Dust is also categorised as an outdoor and indoor pollutant in this context. Pollutants may also be generated internally by objects - for example, the deterioration of cellulose acetate film results in the generation of acetic acid, which can damage other objects nearby.
Physical forces
This category includes sources of mechanical damage, where objects may be bent, broken, distorted, abraded, worn etc. The change occurs by some applied force, which may be as varied as seismic movement from earthquakes, vibration from roads, electrical equipment or amplified music, or from simple handling accidents where objects are bumped or knocked.
Thieves and vandals
At times referred to as 'criminals', this category includes deliberate theft or damage to cultural heritage. Many famous examples exist, such as the 1990 [of paintings from the Isabella Stewart Gardner Museum], though it is likely many thefts go unreported or even unnoticed.
Water
Water damage usually occurs through leaks in building fabric or through flooding, associated with weather events or the malfunction of water-carrying infrastructure (plumbing, wet pipe sprinkler systems, air conditioning). Condensation may occur where the temperature of the air drops suddenly, as when warm indoor air hits a cooler external wall or window. Water may soften or solubilise applied media (paints, adhesives, coatings), cause physical damage through impact, and swells and distorts organic media. Water can also carry pollutants and contaminants, such as mud and sewage. The 1966 Florence flood was a formative moment in the development of the conservation-restoration profession.
Other frameworks
This is not the only framework used to categories the deterioration of materials in cultural heritage professions. For example, deterioration may also be categorised according to source: biological, chemical, physical [ref].
Sustainability
The ten agents of deterioration are often used to frame discussions about sustainability in the cultural heritage sector, when the cost of controlling or minimising deterioration is compared to the perceived benefits. Costs may be financial (e.g. the cost of running air conditioning), environmental (e.g. the use of plastics as storage and packing material, or the use of solvents for conservation treatment) or even the labour required to sustain an activity. The repercussions of established conservation-restoration practice on the environment and on climate change are increasingly debated, particularly the profession's emphasis on tight control of temperature and humidity.
Recent environmental guidelines for cultural heritage collections, such as those developed by the Australian Institute for the Conservation of Cultural Materials (AICCM),[3] emphasise sustainability and resilience as a guiding principle and directly reference climate change as a reason for frequent review.
References
Michalski. S., ‘An overall framework for preventive conservation and remedial conservation’ in ICOM Committee for Conservation 9th Triennial Meeting, Dresden (1990) 589-591. Waller, Robert. 1994. ‘Conservation risk assessment: A strategy for managing resources for preventive conservation. Preprints of the Contributions to the Ottawa Congress, 12 ‑ 16 September 1994, Preventive Conservation: Practice, Theory and Research. London: IIC. A. Roy and P. Smith (Eds.). Available at http://www.konservaattoriliitto.fi/060513/Offprint%201.pdf or http://www.museum-sos.org/docs/WallerOttawa1994.pdf https://www.canada.ca/en/conservation-institute/services/agents-deterioration.html https://www.museum-sos.org/docs/WallerOttawa1994.pdf