Collection maintenance is an area of collections management that consists of the day-to-day hands on care of collections and cultural heritage. The primary goal of collections maintenance or preventive conservation is to prevent further decay of cultural heritage by ensuring proper storage and upkeep including performing regular housekeeping of the spaces and objects and monitoring and controlling storage and gallery environments. Collections maintenance is part of the risk management field of collections management. The professionals most involved with collections maintenance include collection managers, registrars, and archivists, depending on the size and scope of the institution. Collections maintenance takes place in two primary areas of the museum: storage areas and display areas.
Collection maintenance and its tasks all work as a means to continually observe the condition of collections and ensure they are properly maintained and cared for. Because museums and repositories are stewards of cultural property in the public trust, they have a "responsibility to provide reasonable care for the objects entrusted" to them. Museum's collections maintenance tasks can also involve assessing and implementing strategies to improve storage areas and containers while continuously monitoring environmental conditions that may affect objects.
The collections management policy of an institution should include sections that address storage, integrated pest management, conservation, record management and documentation, inventories, and risk management. These policy sections should guide the scope of collections maintenance and designate responsibilities with staff members. A Collections Management Policy is considered a core document meant to support Collections Stewardship Core Standards and may be updated periodically to reflect best practices best served for a museum's specific collection.
Agents of Deterioration
Agents of deterioration are forces which act upon materials and cause them to degrade over time. There are ten main agents of deterioration which should be monitored on a regular basis and guarded against as a part of collections maintenance. These are temperature, incorrect relative humidity, light, dust & pollutants, pests, physical force, theft & vandalism, fire, water, and custodial neglect. It is important to recognize the type of damage each agent may present as well as ways to mitigate harmful effects.
Environmental conditions are highly controllable in most indoor situations. They include the temperature, relative humidity, light levels present in a collection space on any given day, and contaminants. Some flexibility is naturally built into most collections when it comes to the temperature and humidity changes they can bear, allowing for conditions to vary somewhat in response to the outdoor environment of a location.
Two types of light offer potential decay to cultural heritage: ultraviolet (UV) light and visual light (light that can be perceived by the human eye). Although they can be affected simultaneously by removing light sources, reducing overall intensity, or increasing the distance between a light source and an object, best preventive practice treats these types of light separately due to their differences.
Contaminants can come in many forms including naturally occurring chemical breakdowns in certain compounds, particulate pollutants, and accidental human contamination. Protecting collections from contaminants can be as simple as creating barriers to prevent abuse or as complicated as taking preventive actions to protect an object from its own chemical breakdown.
Temperature Temperature acts primarily in conjunction with relative humidity, but it can trigger damage in its own right. Extreme high temperature can cause structural damage to some materials; paint may become brittle in excessive heat and some plastics may soften or melt in the heat. "High temperatures also accelerate chemical and biological processes," which can lead to corrosion or embrittlement of material. Insects also thrive in warm environments, and so temperatures should be kept as "cool … as practicable in storage and display areas".
Any storage or display situation must take into consideration the temperature at which collection permanence can be optimized, and systems should be in place that aim to meet that standard, ideally in conjunction with efficient use of energy and funds. Different materials react to temperature in different ways. For example, ceramics are vulnerable to direct heat on a mechanical level, but many organic materials are at greater risk of undergoing phase transition if the temperature becomes excessively cold. One rule of thumb applies across the board: the rate of chemical reactions is dependent upon temperature in such a way that higher temperatures reduce the activation energy and hasten chemical degradation processes.
Human comfort levels must also be considered. Storage areas can often get away with slightly lower temperatures than display areas since they are not accessed as often, and it is most likely that those who do enter the space will be prepared for the conditions. In galleries, however, viewers must feel comfortable enough with the temperature to spend time there, otherwise the collection will simply not be viewed and lose its purpose in being on display.
Incorrect Relative Humidity
Moisture has strong effects on nearly all cultural heritage materials, with ceramics and glass being exceptions to these effects in most cases. Metals face the risk of corrosion as RH increases, a risk which is enhanced by surface contaminants and emphasizes the need for proper housing. Additionally, mold growth is far more likely as humidity increases, which not only could cause allergic reactions for viewers but it also weakens the collections afflicted and attracts other pests. In contrast to this requisite for dry conditions, if the atmosphere is not humid enough wooden objects could crack or warp, and many organic materials face embrittlement below 40% RH.
Relative Humidity (RH) is the amount of water held in the air as a percentage of how much could be held in fully saturated air at a given temperature. The possible amount of moisture held at a given time is directly related to temperature. Warm air can hold more water than cold air.
It is important to measure the RH of spaces regularly by using a number of tools including humidity indicator cards, thermo-hygrographs, hygrometers, psychrometers and data loggers. Once these data are being monitored, there are several ways to adjust relative humidity by using humidifiers, dehumidifiers, improving heating and air conditioning systems, and adjusting the temperature of the space.
In recent decades, it has become understood that even delicate organic materials have some elasticity in their response to relative humidity (RH) fluctuations, allowing the materials to swell or contract as necessary. This phenomenon is naturally reversible within a range of 50% ± 15% RH. Destructive chemical and mechanical processes, such as hydrolysis at high RH and embrittlement and cross-linking at low RH, can be held to a minimum within a similar range for a general museum collection.
Although minor and gentle fluctuations in RH can reasonably be withstood by most collections, quick or drastic shifts can be harmful. Anisotropic materials such as wood and ivory are especially responsive to humidity changes, and RH issues are compounded when they are attached to inorganic materials such as a metal. The metal acts as a restraint, hindering the organic materials' ability to expand and contract as needed. Thus, cultural heritage objects composed of highly responsive materials or a combination of organic and inorganic materials should ideally be in carefully controlled climates and buffered against the atmosphere by their display or storage housing.
Damage due to incorrect relative humidity occurs in conditions where high percentages (wet) and low percentages (dry) are present. High relative humidity can result in mold growth, salt efflorescence, rapid corrosion, and swelling of wood. Low relative humidity can result in cracking of wooden objects and embrittlement of paper and organic textiles. Rapid fluctuations in relative humidity can also be damaging, as "Rapidly fluctuating temperature and relative humidity compound all of these effects." Institutions should aim to keep the RH constant in exhibitions and storage areas because many organic objects expand and contract as both temperature and RH change.
Some changes undergone by objects are reversible by adjusting the RH, but damage like cracks may be irreversible. Keeping the RH within an appropriate range for the type of material and as consistent as possible will prevent most RH based damage. Limiting storage and display spaces to between 40-60% RH will avoid most damaging effects, but maintaining a stable RH is considered more important than adhering to absolute ranges.
Light
Light, as it relates to collections maintenance, is primarily concerned with the visual and ultraviolet light (UV) ranges of the electromagnetic spectrum. Both types of light can cause damage as "light radiation falling on a surface provides energy to induce chemical changes in the molecules of the material." Damage from light, including loss of color and strength, is cumulative and irreversible. It is therefore crucial that light levels are monitored.
Visible light Visual light, measured in lux or foot-candles (fc), cannot be eliminated, as it is required both to view collections in detail and to move safely in the presence of collections. Unfortunately, this means that harmful oxidation effects which visual light makes possible also cannot be eliminated, but merely reduced to the amount necessary for the task at hand.
The effects of visual light began to be studied by artists and color manufacturers as early as the 18th century, but it was not until the mid-20th century that the chemical damage caused by different lighting situations was researched in depth. In recent decades the cumulative nature of light degradation has become better understood by conservation science. Comprehensive studies began to emphasize long-term effects and allow for short-term variation in light levels depending on the specific situation: standard viewing, viewing by the aged, complex study or treatment, and observation of low contrast details all may have different requirements. Practical compromise between protection of cultural heritage and allowing the artifacts to fulfill their visual purpose means there is an allowance of some physical risk.
Even with this flexibility, light interaction should be limited to moments when an object is on view or undergoing study, and the level of lighting should be chosen accordingly. According to Museum Registration Methods, 5th edition, the suggested light levels for certain types of objects is as follows:
"The traditional recommended light level for sensitive materials—including textiles, botanical and zoological specimens, pigmented objects, works on paper, and organic materials such as feathers, furs, and skins—is no more than 50 lux or 5 fc. Moderately sensitive materials, such as oils and acrylics on board and composite inorganic objects, should be exposed to light levels of not more than 150 lux or 15 fc. The traditional levels recommended for the least light-sensitive materials, such as stone, ceramics, metals, and glass, are not more than 300 lux or 30fc."
Because lighting effects are cumulative, any limit in exposure – whether in time or in intensity – prevents material degradation. A period of intense or lengthy light exposure should be balanced out with periods of low exposure.