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will develop tight edges and baggy centres if they lose too much moisture. Repeated cycling may lead to permanent
damage (Thomas, 1987).
To some extent the relative humidity can be controlled by using suitable cotton carp ets of reasonable thickness
on the floor of the gallery, as these carpets absorb sufficient moisture from the air (Swarnakamal, 1975). At a 1993
seminar on Preventive Conservation in Latin America most participants agreed that protection from damp
environmental conditions had to be given p riority. It was pointed out that this preventive effort would do more for
the long-term preservation of collections than any individual or mass treatment (Raphael, 1993). A popular way to
reduce the high moisture levels in the air is the use of portable dehumidifiers or moisture absorbing crystals. Small
low wattage (50–100 watt) heaters can also be used, though only in very small, confined areas. They too help reduce
the moisture from the air. They are not expensive nor do they consume large amounts of electricity (Ling, 1998).
In 1997 the Getty Conservation Institute started a project that focuses on develo ping economical and sustainable
strategies to improve physical environments of collections in historic buildings in hot and humid regions. The project
aims at researching alternatives to conventional air-conditioning systems by studying the control of relative humidity
through ventilation and heating, while allowing larger variations of temperature. The institute developed a set of
guidelines for evaluating the environment of museum collections and their buildings (see GCI website).
Thus the control over temperature and relative humidity is generally accepted as a method of reducing
degradation of collections.
The maintenance of storage conditions to established parameters is the most vividly discussed issue in storage
conditions; proper temperature and relative humidity are the subject of continued debate. Yet most researchers tend
to agree that the present norms for all archival materials are too tight and that stability of both temperature and
relative humidity is at least of the same importance (Banks, 1999; Buchmann, 1998; Christoffer-son, 1995; Porck
et al., 2000; Rhys-Lewis, 1999). Norms for both temperature and relative humidity depend largely on loca l climatic
conditions (Thomas, 1987). Strangely enough these are not always taken as a standard. Any tropical institution that
tries to achieve the environmental control specified in standards for temperate zones is likely to give up and not even
exercise the control measures available to them (Ballard, 1992; Clements et al., 1989). It is of the utmost importance
that keepers of important cultural collections are aware of the diverse standards and differing prerequisites. What
is a minimum in one country can be a maximum in others, and may be regarded as an optimum in another (Fröjd
et al., 1997). One should not lose sight of the fact that any standard is nothing more than a set of compromises
among the participants (Shahani et al., 1995).
Temperature and relative humidity data have been the most frequently reported over the past 20 years, but the
results are often of little practical use, due to the limitations and unreliability of the monitoring. Reliable monitoring
data is essential before deciding on the performance of a building; it will illustrate whether the building helps or
works against the preservation of collections. A guide to external conditions can be provided by the data from the
local meteorological office, if not too far away from the location. Several guidelines for designing a monitoring
system should be followed in order to o btain reliable p arameters (D aniel et al., 2000) and some monito ring reports
have been published over a period of 10 years ( see also Rosenberg, 1986).
In a PhD-study on museum environme nt in Brazil two naturally ventilated historic buildings from the 18th and
the 19th centuries were compared with a modern air-conditioned one. In this study the 19th century building had
the most stable climate prob ably caused by its veranda coupled with its opening regime. On the other hand, the 18th
century building was the most problematic, probably due to its thermal inertia, coupled with its opening regime
(Toledo et al., 1998b). On a microclimate level both Kamba and Stolow studied the use of natural materials as
buffers for relative humidity (Kamba, 1987; Stolow, 1966).
The relationship between relative humidity and temperature is excellently shown in the Preservation Calculator
from the Image Permanence Institute (IPI). It shows the natural ageing rate of organic materials at a certain
temperature and relative humidity, how long it takes, for example, for paper to become brittle, and how long it takes
for mould to grow under specified conditions. It works with the so-called Preservation Index (PI), a concept
introduced by the Image Permanence Institute in 1995 to express the ‘preservation quality’ of a storage environment
for organic materials. The Preservation Index has units of years that reflect the possible problematic behaviour of
the preserved objects. The higher the Preservation Index, the better conditions are for preservatio n of organic
materials. Preservation Index values in years were designed so that the Preservation Index of 20�C and 45% relative
humidity (recommended conditions) was 50 years. However, the recommended conditions were set for temperate
climates and not for tropical ones. Nevertheless this tool, which can be downloaded freely from the IPI website,
gives a good insight into the relationship between temperature and relative humidity.
See also Agrawal, 1977; Brommelle, 1968b; Drummond, 1999; Erhardt et al., 1994; Freemantle, 1988; Grove,
1961; Gut, 1993; Kamba et al., 1988; Lull et al., 1995; Padfield et al., 1990; Scott, 1994.
5.2.1 Air-conditioning
Air-conditioning is frequently not an option for archives in developing countries. That is why passive climate control
offers a more attractive way to control the physical environment. Air-conditioning might be an answer to control
excessive heat and relative humidity, but it is not one that many can afford. It is not just the cost of installation, there
is the need to maintain the system and the running cost, i.e. the electricity bill (Agrawal et al., 1974; Akussah, 1989;
Aranyanak, 1988; Coates, 1995; Karim, 1988; MacKenzie, 1996; Toledo et al., 1998b). Even in the 1960s caution
was being recommended (Rousset de Pina, 1961). One report from Sierra Leone shows that of the air-conditioning
systems acquired in the late 1960s and early 1970s, all except one had become defective and neither repair nor
replacement proved feasible (Wagner, 1985). In Nigeria none of the original centralised air-conditioning systems
proved functional. They were replaced by unit or split systems (Egbor, 1985). There is much debate about
centralised whole building systems or sp lit systems, although the outcome of the experiment at Jos U niversity in
Nigeria, where 16 different units were installed, was very positive. Using decentralised systems reduces the chance
that the whole building will be without air-conditioning. Most of the authors want to avoid central air-conditioning