B E R O A R C H I T E C T U R E P L L C A R
C H I T E C T U R E S U S T A
I N A B I L I T Y P R E S E R V A T I O N
SOME THOUGHTS ON MUSEUM ENVIRONMENTS IN EXISTING BUILDINGS
The New Orleans Charter [for Joint Preservation of Historic Structures and Artifacts] is the product resulting from the two symposia: Museums in Historic Buildings held in Montreal, Quebec (1990) and New Orleans, Louisiana (1991) and co-sponsored by the American Institute for Conservation of Historic and Artistic Works (AIC) and The Association for Preservation Technology International. This Charter has been officially adopted by the Board of Directors of both AIC and APTI. The New Orleans Charter was subsequently adopted by the National Conference of State Historic Preservation Officers at its Annual Meeting in Washington, D.C. in March, 1992.1 Arising from a concern for the coexistence of historic structures and the artifacts housed within them; Recognizing our responsibility as stewards to provide the highest levels of care for the structures and other artifacts placed in our care; Recognizing that many significant structures are used to house, display and interpret artifacts; Recognizing that historic structures and the contents placed within them deserve equal consideration in planning for their care; Recognizing that technologies and approaches will continue to change; and Recognizing that those involved in preservation are part of a continuum, and are neither the first nor the last to affect the preservation of historic structures and artifacts; We, therefore, adopt these principles as governing the preservation of historic structures and the artifacts housed in them:
1.Institutions' statements of mission should recognize the need to preserve the unique character of both the historic structure and artifacts.
2.The preservation needs of the historic structure and of the artifacts should be defined only after study adequate to serve as the foundation for the preservation of both.
3.Requisite levels of care should be established through the interdisciplinary collaboration of all qualified professionals with potential to contribute. 4.Appropriate preservation must reflect application of recognized preservation practices, including assessment of risk before and after intervention, and the expectation of future intervention.
5.Measures which promote the preservation of either the historic structure or the artifacts, at the expense of the other, should not be considered.
6.Regarding public use, the right of future generations to access and enjoyment must outweigh immediate needs.
7.Appropriate preservation strategies should be guided by the specific needs and characteristics of the historic structure and artifacts.
8.Appropriate documentation of all stages of a project is essential, and should be readily accessible and preserved for the future.
9.The most appropriate action in a particular case is one which attains the desired goal with the least intervention to the historic structure and the artifacts.
10.Proposed preservation strategies should be appropriate to the ability of the institution to implement and maintain them. There is a conflict between the need to preserve existing buildings and the need to preserve collections: conditions which are ideal for a collection are not always ideal for a building. This is typical for all museums in buildings which are not built specifically to house collections and has led to the adoption of the New Orleans Charter. The discussion which follows, and the subsequent recommendations, are intended to comply with the Charter. The environmental factors considered include relative humidity, ambient temperature, light, ventilation, and air quality. Each is discussed separately below. The most important environmental characteristic to control is relative humidity. High humidity leads to unwanted biological growth such as mold and fungi, low humidity to brittleness in some materials. Rapid variation in humidity stresses all materials but is particularly harmful to objects composed of multiple pieces attached to one another (as in furniture). In this climate, low humidity is a problem in heated buildings during the winter and high humidity during the summer. Objects conservators generally recommend using mechanical humidification and de-humidification to maintain humidity in mixed collections at 50%, + 5%. Building Conservators recognize bad effects on buildings from humidity extremes. In the summer, high humidity during
warm
weather nourishes molds and fungi. But de-humidification is usually
only partially effective,
primarily because of air leaks through the building
envelope. Building conservators find that
constant 50%
humidity can only be achieved under highly
controlled circumstances, not achievable in an
existing building without damaging the historic
fabric. It is
possible
to reduce humidity variation by taking advantage of the buffering
effect of the
building envelope, and using the heating system for limited control of
humidity. Since the
relative humidity is driven down by heating a space, heat should be
kept to a minimum
during the cold, dry season. When there is danger of biological growth
(humidity above
65%) spaces should be heated to reduce the humidity. It is
not
possible to obtain optimum humidity in most buildings for the
collection without
damaging the building. The best that can reasonably be achieved is
probably a gradual
seasonal change from about 60% in the summer to about 30% in the
winter. If the gradual
change is to be achieved, air changes must be minimized; windows and
doors must be kept
closed, and the heating system controlled with a humidistat. High
temperatures accelerate chemical decomposition. Cold temperatures cause
freezing. Objects
conservators recommend a
constant, cool temperature to reduce the
physical stresses caused by differential
expansion and contraction of materials. Furniture is particularly
susceptible to
variation in temperature and plywood or
veneers are at great risk from large
variations. Any temperature swings should
be gradual. Optimum conditions for
mixed collections are 65º F + 5º F, year
around. Building
conservators are less concerned
with temperature variations except for
rapid fluctuations and freezing. If a
building is equipped with a heating
system, one of the easiest variables to
control is low temperature. Except for the
danger of pipes freezing, the building is
not terribly sensitive to variations in
temperature and, in fact, since many
existing buildings were traditionally
unheated in winter, interior temperature is
perhaps best allowed to float with the
exterior temperature, provided the pipes
are drained. This reduces the incidence of
ice damming at eaves, as well as physical
stress on components, such as doors and
windows, which are subject to differential
temperatures on opposite sides. The most
effective control of (infrequent) high
temperatures is to keep a building shut,
with windows draped or otherwise blocked
during warm days, opening it to cool
breezes in the evening. Combining
these needs, the optimum temperature compromise is one which allows
modest
gradual changes in temperature with the seasons. If there are water
pipes in the building, the
lowest temperature in winter should be above freezing. The highest
temperature in summer
should be the ambient temperature, as buffered by a closed building and
drapes or shades. If
the heating system is controlled by a humidistat, it should have a low
temperature thermostat
override to prevent the pipes from freezing. Light
induced
deterioration primarily affects organic materials. Light is a form of
energy that
breaks chemical bonds, thus causing decay. The damage caused by light
depends mainly on
the nature of the object, the relative humidity, the kind of light or
other radiant energy present
(e.g. UV, IR), the intensity, and the duration of exposure.
Light-induced deterioration is
controlled in various ways, but principally by minimizing illumination
intensities and
duration, and by storing objects in dark places.
2
Objects conservators recommend
storing objects in
the dark. Objects on display should be lighted with
the minimum light necessary to reveal the object,
and only when the object is actually being viewed. Valuable objects
should be displayed for the
shortest length of time possible, never on
permanent display. Building conservators are aware of
the need to
display historic buildings in order for them to have
educational value. To be displayed properly, they
must be shown in light. Damage from light
generally cannot be prevented on the exterior
except through the use of protective coatings. In
the interior, conservators recommend blocking the
light with opaque blinds or shutters when the
building is unoccupied, and filtering the light when
the building is occupied. Artificial light should
used as little as possible and at the lowest intensity
compatible with proper display. Regarding
the
exterior, keep exterior wood painted. Masonry and tinted cementitious
materials tend to fade but degrade slowly, if at all, with exposure to
light; since fading is an
inherent characteristic of the materials, it is appropriate to allow
the natural color shift. Regarding
interior window coverings, there are several alternatives: 1. Leave
the windows undraped. Accept light-induced deterioration as the price
of interpretation, and; a. Provide
temporary blinds which can be inserted when the building is
empty, or, b. Provide
film or plexiglass filters. We do not generally recommend the
use of films: drawbacks include gradual (invisible) loss of UV
filtering
effectiveness, and damage to original windows when films must be
replaced. Plexiglass is preferred for its durability and ease of
replacement. Select plexiglass filters with 100% UV screening and the
highest degree of visible light screening which does not appear
offensive. 2. Provide
heavy drapes. Keep them closed when spaces are unoccupied. Pollution-induced
deterioration refers to air-borne particles and chemicals. The effect
of such
deterioration varies widely depending on the specific material involved. Objects
conservators recommend reducing
air flow to the minimum acceptable, and
enclosing particularly sensitive materials
(for example silver) in air-tight containers. Building
conservators recommend control
of pollution-induced deterioration
principally by filtration of induced air. For this to be effective, the
envelope of the
building must be relatively air-tight, and
fresh air limited to that necessary for
ventilation purposes. Fans are required to
move the air. There is
a
conflict between displaying a building as it was originally intended to
be used, and
conservation of both objects and the building. But most building
materials are not highly
sensitive to this type of deterioration. If there are sensitive objects
in the collection they
should be displayed as little as possible, and under cover if possible.
Windows should be
kept closed. All of
the
above discussion is based on general principles of building and
collection care. In
order to make specific recommendations and to design improvements it is
necessary to have
actual measurements of the variables discussed above, as well as a
well–articulated,
institution-wide, preservation and interpretation philosophy. Data
collection. To make recommendations for permanent improvements to the
interior
environment it is necessary to understand the present interior
conditions and exterior
microclimate. Monitoring equipment can be hygrothermographs or
dataloggers (dataloggers
are preferred). At least one device on each floor and one in the
basement should be
monitored for at least a year. The microclimate may be quite different
from the local airport
or other location where weather observations are being made. To
understand the local
climate, weather observations should also be made outside, on site, for
at least a year. 1. The quote is copied from the palimpsest.stanford.edu website 2. "New Tools for Preservation," Reilly, Nishima, and Zinn, Image Permanence Institute, Rochester Institute of Technology, 1995.
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