- Light
Apart from other causes earlier discussed, light can, to a large extent, be regarded as an independent and prime cause of deterioration of museum objects. The type of materials forming part of the museum collection that are subject to damage by light are pigments and dyestuff, including inks; paper and other cellulose materials; and, various other organic materials.
Pigments and dyestuff fade when exposed to light and this is very noticeable in water colors. Unfortunately, colors fade selectively, some disappearing while other remain unchanged, which means that the color relationships of a painting can be grossly distorted.
Rapid and serious deterioration of paper is caused by the oxidation of cellulose brought about by the ultraviolet rays in sunlight and fluorescent light. There are two effects of light on paper that result in its ultimate embrittlement and deterioration. First, it has a bleaching action that causes some whitening of paper and fading of colored papers and certain inks. Second, it causes any lignin, which may be present in the paper, to react with other compounds and turns it yellow or brownish. It is this reaction that results in newspapers’ turning yellow on exposure to light. Certain invisible changes also occur at the same time when these visible effects of light are taking place. Fibers in the paper are broken into smaller and smaller units until they are so short they can no longer maintain the bonds necessary to hold the paper together. Some woods bleach under the action of light; some turn “yellow” and some darken. Unfortunately, the reactions initiated by light continue after the source of the damage has been removed.
- Incorrect Temperature
Organic materials all contain moisture; they absorb and give off
moisture and try to find a balance between their moisture content and that in
the air around them. If the relative humidity (moisture content) in the air
goes up, they will absorb moisture and swell, and if it goes down, they will
give off moisture and shrink. If this occurs slowly and moderately then no
damage will be caused. However, sudden, large and frequent relative humidity
fluctuations can cause shrinkage, warping, splitting, and general aging of
objects made of organic materials. A sudden increase in relative humidity can
cause condensation on metal artefacts, which will promote corrosion. In general, high temperatures accelerate chemical reactions,
causing deterioration to occur in all formats. Cooler temperatures are
essential to long-term preservation. Fluctuations in temperature also damage
records.
Extremely dry or extremely humid
environments damage all record formats. Mold and rust can develop in humid
environments while dry environments cause paper, film, and other materials to
become brittle. Fluctuations in relative humidity cause materials to expand and
contract as they absorb and release water which can lead to mechanical damage.
The detrimental effects of incorrect temperature (either too high or too low) are often observed after considerable time has passed and so the slow deterioration that results is often underestimated.
Temperature and relative humidity have been shown to be interdependent. Hygroscopic materials that normally contain moisture are the most sensitive to over-drying. These hygroscopic materials are those of organic origin and of fibrous or cellular structure, such as paper, parchment, papyrus, leather and notably the adhesives used in bookbinding. Paper and related materials, on the other hand, deteriorate rapidly with temperature and relative humidity changes.
The greatest danger that can arise from an excessively high relative humidity is the tendency for molds to grow on any material that can provide nutriment, such as glue, leather and paper. The presence of mold growth is a warning that the atmospheric relative humidity is above the limit of safety. If too high, humidity hastens acid deterioration. When conditions are favorable to mold growth, for example, in a library, a gray dusty bloom is observed in the first instance on the darker bindings, and it soon becomes fluffy with a tendency to be organized in circular patches.
There are some evidence that regular changes in temperature and relative humidity (cycling) can lead to weakening of paper and related materials, as a result of internal stresses set up in them in response to these changes. There are no firm data to indicate how serious this effect may be, but scientists do not believe that it results in measurable damage to these materials if such changes in temperature and relative humidity can be held to less that 10 degrees and 15%.
- Custodial Neglect & Dissociation
One type of custodial neglect occurs when active care is not taken to preserve the collection or when information and practices on collections care are not current. The second type of custodial neglect is the disassociation of collection objects and their records.
In the majority of situations the conservation and security precautions in the archive are sufficient to prevent accidental damage, negligence and to inhibit the less determined vandals. These measures include physical or psychological barriers, such as floor elevation, ropes and stanchions or the total encasement of the object in show cases. These barriers will deter visitors from approaching too close and touching, making or accidentally scratching the objects. However, mischievous visitors will find ways to outwit the guard. Other means of security protection depends on the guard’s perception of deviant behaviour in visitors.
