The word "furniture" tends to evoke only thoughts of wood. However, furniture may have components of every conceivable material, including metal, bone, plastic, shell, leather and fabric, as well as paints and natural and synthetic resins. All these materials must be taken into account to properly care for and maintain furniture.
The practice of caring for historic furniture has changed dramatically in the last few years. Until recently, furniture was viewed as primarily functional, and thus it was considered acceptable to repair damaged or broken furniture with whatever means were available so it could be used again. If the paint or varnish was in poor condition, it was routinely removed and replaced with new paint or varnish, or in some cases simply coated with a new layer of finish over existing layers. Today, the monetary, cultural and artistic values of historic furniture demand that the "age old" practices be reviewed.
Effects of the Environment
The environment can have a profound effect on the preservation of furniture.
Light, particularly visible and ultraviolet (UV) light, is very damaging to organic materials such as wood. Damage from light is cumulative and irreversible. A table top exposed to diffuse light for several years will suffer similar effects of light damage as a table top exposed to direct sunlight for a shorter time. Light provides the energy and increased temperature necessary to chemically degrade finishes and wood colorants, and in severe cases, cause the wood cell structure to break down. Clear finishes often turn yellow or opaque in response to light, and the color of the wood itself can also change. The resulting damaged finishes and bleached wood cannot be restored to their original color without stripping and refinishing, a practice not recommended as loss of the "patina" or evidence of use can affect the furniture`s monetary value.
To limit the effects of light, move all furniture out of direct sunlight, utilize blinds or curtains to block the intensity of sunlight and allow it to diffuse evenly throughout a room, and keep lights in rooms turned off when not in use. UV light, which is particularly damaging to wood and fabrics, can be screened out by applying a UV-filtering film to windows.
Furniture can also be affected by the amount of moisture in the air. Wood and other organic materials respond to changes in relative humidity (RH) by expanding or contracting as they try to maintain equilibrium with the moisture in the environment. Ideally, RH levels should be maintained within a 40%-60% range. If the RH is too high (above 70%) wood and other materials expand. If they are constrained in any way, they may split upon shrinking when the RH drops to a lower level. Furniture finishes are also affected as differences between the response of wood and its coating to changes in RH may eventually cause a coating to detach. A prolonged high humidity environment will also promote the possibility of mold growth and insect infestation. To prevent damage, place furniture in areas of minimum temperature and RH extremes, thereby avoiding attics, basements, active fireplaces and heating vents.
Monitoring temperature and RH in an environment can be done with small, inexpensive thermometers and hygrometers purchased at electronic or hardware stores. When necessary, the RH can be modified to stay within acceptable ranges through the use of humidifiers and dehumidifiers.
When environmental conditions are favorable, organic materials including wood, leather and horsehair are vulnerable to infestation by a variety of insects. A common furniture pest is the powderpost beetle, less than a quarter inch long, which lays its eggs in small crevices. The insect larvae burrow into the wood creating networks of tunnels or galleries as they eat their way along the grain. As they mature to adults they bore out of the wood leaving an "exit" or "flight" hole and fly off to lay their eggs, completing the cycle.