pigmented colorants: dependence on media and time - Cornell ...

corrode the surfaces of materials. Fluctuating temperature and pressure condi-
tions tend to cause materials to periodically expand and contract. As a result, the
undue stresses promote warping and cracking in some materials. Other materials
are sensitive to the oils and wear from human touch.
The phenomenon of natural material change is also subject to location. Marine
environments contain higher levels of moisture and salt, while urban areas expe-
rience a higher concentration of abrasive chemicals due to industrial smog. Both
are detrimental to the longevity of exposed materials.
This behavior is what drives museum curators and art historians to protect their
collections vigorously, attempting to preserve the work for the next generation and
beyond. Very regimented control is kept over all of the conditions in a museum,
including the temperature, humidity and light levels. In many circumstances,
paintings and textiles are protected with glass coated with ultraviolet filters to
remove extraneous light. Patrons are urged not to use flash photography (if at all)
to save expediting the adverse effects. Some institutions even have carbon filters
to purify the air in which the artifacts reside. The most precious documents of
the United States are enclosed in a special casing with only inert gas. All of these
precautions (and more) are done to minimize any possible future deterioration of
the collections.
Artwork that remains in situ, or in its original location, does not benefit from
the protections available in a museum. Examples of such work include architec-
tural decoration or paintings directly on the walls or ceilings of buildings. Such
work has been subjected to harsh conditions over the years. Atmospheric con-
ditions are generally unable to be controlled for these works, and moisture and
temperature variations will inevitably deteriorate the materials. While all work
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