Wood
This article originally appeared in Exchange,
a newsletter published by the Wisconsin Historical
Society. (Volume 29, Number
4, Autumn 1987) It is the 13th in a series of articles
titled Conservation Corner.
The series features information about maintaining
an adequate environment for the storage and exhibition
of historical collections, employing proper collection
care techniques, and recording and cataloging historical
collections. This article was written by Tom McKay,
retired local history coordinator for the Wisconsin
Historical Society.
Elementary school grammar teachers have a favorite and often-invoked
rule of punctuation, "When in doubt, leave it out." The spirit of
this admonition can help local historical societies
provide proper care for their collections. Too often, the caretakers
of historical collections look for miracle treatments for artifacts
when the objects would be better left alone. Artifacts made of wood
have suffered from ill-advised treatments as much as any class of
historical material.
Household wood treatment products abound that are formulated to make
the surface of wood look better. They contain oils, silicones, and
other ingredients that will give a shine or glisten to finished or
unfinished wood. Looks can be deceiving. These products can do little
but harm wooden artifacts over the indefinite time span that museums
strive to hold objects in their collections. Such products have no
impact on the primary need of artifacts made of wood--the need for
a stable environment. Further, oils, silicones, and other products
can build up on the surface of wood over many years and eventually
leave a surface that is cloudy, darkened or checked.
To provide adequate care for artifacts made of wood, museums must
think beyond the surface of the artifacts and go back
to basics. Wood is an organic material that survives
best in a stable environment with favorable temperature
and humidity conditions. Wood undergoes stress during
rapid fluctuations of temperature and humidity. Humidity
changes, in particular, can cause swelling or shrinking
that results in splits, warps or broken joints for
wooden artifacts. A local museum must operate its heating,
cooling, humidification and/or dehumidification equipment
to minimize changes in temperature and humidity. For
the preservation of wood and the use of a museum by
the public, year-round conditions of 68 degrees Fahrenheit
and 50-percent relative humidity would probably be
optimal. However, a local museum must adjust conditions
to the equipment it has available and its pattern of
use by people. For example, a museum that is closed
for the winter and does not have humidification capabilities
on its furnace would do better to run its furnace at
45 degrees Fahrenheit and achieve 30-percent relative
humidity than set its thermostat at 68 degrees Fahrenheit
and have a resulting 10-percent relative humidity.
Museums cannot overlook the damage that light can do to wood. Like
other organic materials, wood will fade from long-term
exposure to light. Light will also check varnish and
other wood finishes and may even cause the surface
of wood to turn dry and powdery over a long period
of time. Turning off lights and closing shades or blinds
when the museum is not open will decrease light damage. Using cotton
sheets to drape large wooden objects or curtain open storage shelves
offers extra protection from both light and dirt. Dirt and dust in
the museum environment do represent additional concerns in the care
of artifacts made of wood. Dirt can work its way into the open grain
of unfinished wood or become embedded in the varnish or shellac layers
of finished pieces. In either case, removing the dirt may cause damage
to the original surface of the artifact, a treatment as bad as the
disease. As a first line of defense, keep all areas of the museum
as clean as possible. (See another
article in this series.)
Wooden artifacts in stable condition can be dusted
lightly with a soft cotton cloth. For a heavy buildup
of dust on unfinished wood, the cloth can be very lightly
dampened with water. The product, Endust, sprayed lightly
on the cotton cloth will pick up a heavy accumulation
of dust on wood objects with a finish. However, the Endust should
not be used regularly and must never be sprayed directly onto any
object.
Professional conservators expressly condemn the use of oils, silicones, or feeding formulas on artifacts made of wood. If the surface needs protection, conservators suggest wax. Good commercial paste waxes or microcrystalline waxes are suitable for use. The wax should be applied according to product directions and in a thin coat. Take special care to avoid buildup in areas with carvings or incised lines. Wax is a very stable, long-term material. In the home, objects require re-waxing when the wax wears off. Because artifacts in museums are not in daily use, they may go years before they need to be waxed again. Tool handles, store signs, and most artifacts that were never waxed in their normal use should not be waxed in the museum under most circumstances. Even in the use of relatively stable and inert waxes follow the schoolteacher's rule, "When in doubt, leave it out." Wooden artifacts that receive care may be spared the need for treatment.
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