Caring For Your Furniture
Wooden furniture can be a composite of many materials. In more opulent eras, the surfaces of a piece of furniture might have been inlaid with metal, bone, ivory, tortoise shell, glass, stone, leather, mother-of-pearl, or wooden veneers. In addition to being simply coated with a clear or colored varnish, the surface of a piece of furniture could be decoratively painted, japanned (built-up layers of finish, making a raised decoration), or gilded. Each material incorporated into a piece of furniture has its own optimal environmental condition, and each responds differently to temperature, relative humidity, and the effects of light. Meeting the diverse needs of the materials in a piece of furniture involves prevention, care, and conservation.
The environment in which an object is displayed or stored affects its long-term stability by encouraging or discouraging the deterioration of constituent materials. Many environmental factors, including relative humidity, temperature, pollutants, light, and pH, can have an adverse effect on materials.
Fluctuating or extremely high or low relative humidity (RH) may be the single most damaging environmental factor for organic materials in a piece of furniture. Moisture levels consistently above 70% RH can result in mold growth, softening of glues, leaching of soluble salts from glass and stone, and accelerated corrosion of metals. In addition, organic materials are hygroscopic - they can absorb and lose moisture, and the typical response to moisture fluctuations is dimensional change in the material.
Wood, leather, textiles, and varnish can swell and contract in response to changes in RH. Wood can be compressed when swollen and can split when shrunken; joints can be stressed and fibers weakened. Differential rates of movement between diverse materials can cause varnish or other surface coatings to crack or flake off. To preserve your objects, you should control the humidity level in your home, keeping it within the accepted RH range of 35% to 65%. If necessary, supplement standard air conditioning with a humidifier or dehumidifier. Inexpensive RH meters can be found in office supply stores, and more accurate meters can be purchased from Edmund Scientific, (609) 573-6260.
While not as damaging by itself as relative humidity, temperature can accelerate chemical degradative reactions within a material. For example, corrosion in a brass mount will proceed much more rapidly at 90 degrees and 50% RH than at 70 degrees and 50% RH. Elevated temperatures also can cause loss of volatile plasticizers in a finish, leading to embrittlement and cracking.
An unfortunate fact in today's world, gaseous pollutants include sulphur dioxide, nitrous oxide, acid vapors, formaldehyde, ozone, and chlorides from salt air. They can cause yellowing of finishes, accelerated breakdown of paper and textiles, tarnishing and corrosion of metals, and etching of stone. Particulate pollutants, which include dust, cigarette smoke, and industrial fly ash, can cause damage in several ways. They contain abrasive particles that scratch surfaces and they contain mold spores or other organic material that provide a base for mold growth. In addition, they frequently have an oily component that allows particulates to become tightly bound to the surface, and they are hygroscopic, attracting moisture to the surface of the object, where soluble pollutants can dissolve and become chemically destructive. To avoid pollutant damage, objects should be kept as clean as possible, air conditioning filters should be changed regularly, and windows should be kept closed.
All wavelengths of light have sufficient energy to damage surfaces of objects. The shorter the wavelength (ultraviolet), the higher the energy and the more rapid the damage. Damage from exposure to light is a result of chemical reactions, affecting first the chromophores (chemical structures that impart color) in a surface, and eventually the material itself. Light actually can break down the structure of cellulose, the primary component of wood, paper, and cotton.
Pigments, dyes, and natural colors of the wood become faded; leather and textiles are weakened; paper is bleached and becomes brittle. Light damage is cumulative and cannot be reversed. Plastic filters are available for windows and fluorescent bulbs to eliminate higher-energy ultraviolet light; however, a piece of furniture should never be allowed to sit in direct sunlight, and long or regular exposure to strong indirect sunlight should be avoided.
A popular misconception concerning the proper care of wooden furniture is that wood becomes "dry" and needs periodic "feeding." Once cut from the tree, wood does not eat and cannot be "fed." Moreover, unless fungal microorganisms have destroyed the majority of the cell walls, wood never ceases to absorb or lose moisture, so it can never be said to be too "dry." Even wooden objects from tombs of Egyptian pharaohs still have the capability to expand and contract in response to changes in humidity.
The perceived dryness on a piece of furniture is usually a condition of the finish, wherein it has become crackled from age, where shrinkage of the film of finish may have resulted in its cleaving from the wood, and the aged finish is generally covered by a layer of embedded dust. Treating the "dry" wood with an oil can have either of two adverse effects. If the oil is a drying oil (pressed from any nut or seed such as linseed, tung, walnut, or any other plant), as it dries it forms a film by the oxidation and cross-linking of its components. Unfortunately, the process doesn't stop when the film is hard but still clear. The oil continues to oxidize and cross-link, eventually becoming dark, soft, gummy, and very difficult to remove without damage to the original finish. If the oil is a mineral oil (a distilled fraction of petroleum), it will never dry, but can penetrate into the wood through microscopic fissures in the finish, causing dark streaks. Again, the solvents necessary to extract mineral oil from wood are harsh enough to remove original finish and may even remove some of the wood's natural color. Most pump or spray polishes contain drying oils or, worse yet, pure silicone, which cannot be removed with any solvent known to science. Oil soaps contain detergents that may be too harsh for an aged, original finish, and they intentionally leave a film of drying oil. Since the intent of any polish is to brighten the surface of a finish (the polish fills in microscopic scratches and fissures in the finish, temporarily restoring luster and clarity), one wants to use a polish that does not darken and that is easily removable. The best alternative to commercial furniture polishes is a good grade of paste wax. One can buy a can of furniture wax (e.g., Renaissance Wax or Goddard's), but the average paste floor wax (e.g., Johnson's, Behlen's, Butcher's Bowling Alley) contains excellent plant and animal waxes at a fraction of the cost.
What most people think of as caring for their furniture (that is, after protecting it from potential damage due to fire, flood, children, animals, and insects) in reality is caring for the surface. The best way to care for your furniture is to use common sense. Hot skillets can soften a finish and char the wood. Leaking potted plants can watermark the finish, permanently stain the wood, and cause the finish to separate from the wood. Insect-infested wood or dried arrangements can introduce powderpost beetles into your house and furniture. Wipe up spills before they have a chance to do damage; dust with a slightly damp, clean cloth, and dry any excess moisture immediately. Regular use of paste wax will afford some protection against liquid spills and simplify removal of food spills.
It should be noted that there is a great difference between modern finishes and earlier, original finishes. Modern finishes are made of synthetic resins that resist many solvents; early finishes, derived almost entirely from natural plant resins, can be easily damaged or dissolved by such solvents as water, alcohols, and ketones (acetone). They also can be broken down by solutions with a high pH, such as ammonia. Commercial window cleaners may contain both alcohol and ammonia and should never be used on an early finish. When cleaning a mirror, for example, one should spray the cleaner on the cloth, not on the glass, to avoid getting it on the frame.
Most brass polishes incorporate an abrasive and ammonia; besides damaging the finish surrounding a brass pull, the ammonia can penetrate into microscopic fissures in the metal and cause the brass to crack. It is preferable to have brass polished once with a very fine abrasive, then sealed with a clear finish such as an automotive lacquer to give years of use between polishings.
If your antique furniture is damaged beyond normal maintenance, you may want to consult a conservator - a trained professional who can perform treatments that do not remove any original materials from an object (including finish), thereby allowing your furniture to retain its historic and monetary value. A conservator will examine and analyze an object to determine which are original materials, the source and cause of deterioration, and will propose and perform a minimally intrusive treatment, documenting the process. The primary reason for conserving a historic object is preservation by ameliorating damage or deterioration; secondarily, conservation is used to improve an object's appearance for presentation.
Finishes that have acquired years of dirt and hand oils usually can be cleaned to present an appearance that is pleasing but that does not hide the signs of age. Cleanings may be performed using detergent systems, and volatile solvents may be used to remove later layers of varnish that have been applied over the original finish. Such cleanings are always performed cautiously; no level of damage to original finish is considered acceptable.
Restoration versus conservation - where is the dividing line? It is generally acceptable to compensate for losses in original materials. Missing decorative elements may be copied from existing examples, reproduced, and applied to the original, and missing finish may be repaired. It is rarely acceptable to completely re-do the entire surface or whole elements whose original surfaces merely present a worn appearance, attempting to restore the object to its condition when new. Removing original material to improve appearance is never acceptable.
To locate a conservator in your area, the American Institute for Conservation of Historic and Artistic Works offers a referral service. The institute may be contacted at 1717 K Street, N.W., Suite 301, Washington, D.C. 20006; 202-452-9545.
To learn more about the care of furniture, you may wish to consult Caring for Your Collections by the National Committee to Save America's Cultural Collections (New York: Harry N. Abrams, Inc., 1992), ISBN 0-8109-3174-5.
Disclaimer: Due to the complex nature of materials in furniture, items can be damaged easily by incorrect treatment. The Museum of Florida History assumes no responsibility for damage incurred by owners, based on information provided in this article.