Furniture Conservation



   

Caring for Furniture

Wooden Artifacts Group

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.

Insect activity

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.

If flight holes are observed in furniture, it is important to determine if the infestation is active. Active flight holes are light-colored and contain a fine, sawdust-like material called frass. Any material resembling sawdust that appears on the floor underneath a piece of furniture could be a sign of a possible infestation. Frass from an infestation that is no longer active can be dislodged if furniture is moved or jostled, giving an impression of insect activity, but should frass continue to appear after being swept away, it is likely that the infestation is active. If furniture or other wooden objects appear to have active infestation, they should be isolated immediately by placing in a large sealed plastic bag. As fumigation may be the next step, and there are a variety of methods available to accomplish this end, a conservator or exterminator who is familiar with conservation issues should be called immediately.

Housekeeping

It was once thought that furniture needed to be "fed" with various mixtures of oils and other materials to keep it from drying out. These mixtures enhance the appearance of wood temporarily, but ultimately do not keep wood from drying out. No amount of oil will prevent furniture from drying out if the RH remains below 30% for a period of time. A better approach would be to keep furniture in a stable environment. Furniture oils are not recommended for maintenance as many of them contain linseed oil or other drying oils, and when used repeatedly will create a gummy, insoluble surface coating that darkens and obscures the grain of the wood. Other furniture polishes contain non-drying oils such as lemon oil and although they do not harden or darken, they nevertheless attract and entrap dirt and grime. Silicone polishes are also not recommended as they leave a film that is difficult to remove and can interfere with future finish treatments.

The best maintenance for clear varnished furniture is a coating of good paste wax. Wax is a very stable material that does not change chemically over time and provides protection from moisture and airborne pollutants. Good quality paste wax is available in most hardware stores. A thin coat applied following the directions on the can is all that is needed, no more than once a year. It may not be appropriate to wax furniture that is gilded, painted or lacquered, or furniture that has unstable veneers or flaking finish. Consult a conservator if any question about the appropriateness of waxing arises.

Once a protective coat of wax has been applied, dry dusting with a soft cloth is recommended for routine cleaning. Dust and dirt are harmful to finished surfaces and should be regularly removed as they can scratch or otherwise damage polished surfaces. A soft cotton cloth or artistís brush is best for dusting. Feather dusters are not recommended for dusting as the feathers tend to get caught in cracks and crevices and can cause detachment of fragile veneers and gilding. A clean cloth slightly dampened in water may help to remove more stubborn dirt. When dusting, be cautious in areas with loose elements such as veneers, moldings, and metal mounts. Should an element become detached, place it in a plastic bag labeled with its original location on the piece and place it in a drawer or other accessible location until a conservator can reattach it.

If brass hardware on furniture is tarnishing, the owner may want to polish it. In most cases furniture hardware was intended to be brightly polished. Hardware was often given a protective coating of lacquer at the time of manufacture to retain its highly polished appearance. Over time, the coating wears off and the brass underneath is exposed to the air. Although some owners prefer lightly tarnished hardware on an old piece, others who prefer bright gleaming hardware may embark on a regimen of regular polishing. There are many brass polishes on the market. Those that contain ammonia can cause long-term corrosion problems, so it is best to choose one of the polishes that has a mild abrasive embedded in cotton wadding. Ideally, hardware should be removed for cleaning so that the polish cannot come into contact with the surrounding wood. If that is not possible or practical, polish the hardware carefully, confining it to the metal only. A good option to a regular regimen of hardware polishing is to have the hardware coated with clear lacquer.

Handling

Before moving a piece of furniture, examine it for loose or damaged joinery. Once you have ascertained that it is safe to move, remove elements such as shelves, doors, and drawers. If doors cannot be removed, secure them by locking or wrapping the case with soft cotton straps. Tables should always be lifted by the apron or legs rather than by the top, which could possibly detach. Chairs should be lifted by the seat rails and not by the arms or crest rail. When moving a large piece, be sure to lift it and not drag it across the floor, as excessive lateral pressure on legs and feet can cause them to shear off or leg joinery to fail. When transporting furniture in a vehicle, place the object on its back or top, not on the legs. If the piece has a marble top, carefully lift it off and transport or store it vertically, as one would a sheet of glass.

A Few Words on Refinishing

Stripping and refinishing furniture is no longer standard practice. An early finish is as important to historic furniture as are legs or any other element. The finish coating offers important data to researchers and is part of the history of the object and once it is removed, it cannot be recovered. It is also desirable to be able to observe on a piece of furniture patterns of wear that indicate the history of use, which stripping and refinishing can obliterate. The appearance of old finishes can often be enhanced without completely removing them by using cleaning materials tailored for specific conditions. The removal and replacement of a surface finish is considered a last ditch effort after other conservation methods have failed. An aged finish, with a patina that only time can produce, can greatly add to the beauty of an object. The primary goal of any treatment should be to maintain the patina of age.

Conclusion

The topics discussed here are intended to aid the owners of fine furniture regardless of whether the value is monetary or sentimental. The majority of historic furniture is in private hands. Proper care and maintenance is the only way to ensure its preservation for future generations to appreciate. Although some objects may eventually become part of a museum collection, it is nevertheless incumbent on the current owner to provide proper care. As shown in this brochure, many aspects of furniture care are straightforward and can be carried out by an educated owner. Problems that are beyond an ownerís capabilities should be referred to a conservator. AICís Guide to Conservation Services can direct you to a qualified conservator in your area.

Further Readings:

McGiffin, Robert, Furniture Care and Conservation, AASLH 1992, Nashville, TN

Video: Furniture Care and Maintenance; SCRME, Smithsonian Institution, Washington DC

Prepared by Fredrick Vogt, Craig Deller, and Christine Thomson

Carey Howlett, Kathy Gillis, Melissa Carr, Joanna Ruth Harris, and Chris Shelton were the reviewers.

The recommendations in this brochure are intended as guidance only, and AIC does not assume responsibility or liability.

Reprinted with the permission of the American Insitute for Convservation of Historic & Artistic Works, 1717 K St., NW, Suite 200, Washington, D.C. 20006; info@aic-faic.org; www.aic-faic.org.

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