American Conservation Consortium
Nationwide Collections Preservation Services
Preservation and Care of Furniture
Wood, of which the majority of furniture is composed, is an extremely complex material. Specialists have spent their entire careers studying one small aspect of wood and still do not understand it completely. While it is impossible, therefore, to predict exactly what will happen to a specific piece of furniture with the passage of time, a general understanding of the nature of wood allows determination of characteristic causes of deterioration. Wood is anisotropic - its properties are not uniform and are dependant upon the orientation of its cells. The most important of wood's many anisotropic properties to deterioration of furniture is its dimensional response to variations in moisture content, determined by the relative humidity of its environment. Shrinkage in wood from the tangential plane can exceed 10%, while radial plane shrinkage is roughly half this amount. Longitudinal shrinkage normally does not exceed 1/10%. As the relative humidity of the environment rises, wood absorbs moisture and expands. Conversely, when the RH falls, wood gives up moisture and contracts. This process occurs regardless of the age of the wood.
The response of dimensional variation with cycling relative humidity directly manifests itself as damage to furniture. Boards allowed to move unrestrained will suffer, at worst, checking (small splits) at the ends of the boards. However, when the construction of a piece of furniture inhibits free movement, such as cross-grain attachment of wooden members to one another, degradation can result. If attempted shrinkage is prohibited, boards (and veneer) can split. Restricted expansion can result in compression setting of the wood - the physical squeezing together of the wood cells. Returning the board to its original moisture content results in a board that is permanently smaller and possibly split due to restrained shrinkage. The stresses generated by dimensional changes in wood are easily great enough to fracture glue joints with resulting joint looseness and loss of parts, and lifting of veneer. Prevention of damage to historic wooden objects from dimensional variation of wood can be accomplished only by stabilizing the relative humidity of the object's ambient environment.
Environmental factors other than temperature and relative humidity have deleterious effects on wood. Light will bleach the natural colorants found in wood, as well as the original coloring agents applied by the cabinetmaker. In addition, ultraviolet light can damage the cells on and near the surface of wood. Light will cause rapid degradation of finishes, bleaching and severely crazing them and, in severe cases, will result in their cleavage from the wood and loss. Damage from light is not reversible, so furniture should be kept in the lowest light level possible. It is especially important to eliminate ultraviolet light, large proportions of which are contained in sunlight and most fluorescent light bulbs.
Dirt not only obscures the appearance and colors of the surface of furniture, but also contains chemicals that can attack finishes and metal components. Insect infestation, commonly by the larvae of powder post beetles and of furniture beetles, can weaken wood so severely that it is unable to support its own weight. Early detection and fumigation are the solution to such infestations. It is important to bear in mind that adult beetles fly and females can lay eggs on pieces of furniture or other wooden surfaces far from the infested one, so quick action once the problem is discovered is imperative.
Furniture's largest and most damaging pest - man - is also the hardest to control, as fumigation generally is not considered acceptable treatment. Education, while much slower, is a more humane solution to this problem. The issue of damage to furniture caused by man is complicated by the fact that furniture is intended to be used, yet even the most careful use hastens deterioration. Minimization of damage can be accomplished by understanding the limitations and weaknesses of each piece of furniture and using it well within these limitations. In general, this consists of careful use, proper environmental conditions, correct maintenance procedures, and, when necessary, ethical and properly conducted repair and treatment.
Care and Maintenance
"Ideal" environmental conditions for the preservation of furniture are constant relative humidity of 50% (depending upon geographical location), constant temperature of about 45 degrees F or lower, total darkness, no dirt or pollutants in the air, lack of insect infestation, and no handling or use. In most situations, these conditions are impractical. Therefore, it is important to vary from these levels as little as possible, with the knowledge that the amount of deterioration an object will suffer will be directly proportional to the deviation from ideal environmental levels. If one approaches these ideals, the need for additional care or maintenance virtually is eliminated. Rephrased, care and maintenance of furniture consists, first and foremost, of providing the proper environment. Additional procedures only compensate for failings in the previous or current environments.
Dusting may be done with soft cloths, either dry or moistened very slightly with distilled or de-ionized water to hold the dust. A misting sprayer directed at the cloth, not the object, works well. Do not use polishes or dusting aids. An alternative cloth is the Dust BunnyTM. It is woven of two different fibers that, when in association with each other, create a static charge and hold the dust to the cloth. The cloths are reusable, washable and available from the New Pig Corporation (800-468-4647). Be sure to change them as they get dirty.
Do not dust surfaces with active cleaving and lifted paint, finishes, or gesso and gold leaf. Such areas may be able to be dusted with a clean natural bristle paint or artist's brush. Watch carefully for loss of surface and stop if it is observed, referring the problem to a conservator.
When moving collection items to allow dusting, wear clean cotton gloves to prevent corrosion and deterioration caused by hand salts, oils and acids. This is extremely important for metals and textiles.
If the building has an air handling system, consider installing high efficiency filters. Run the system fan continuously all year long. If an air handling system is not present, it is possible that stand-alone dust filtration units can aid in the collection of dust within the building. In order for any type of filtration to be effective, the building must be as tightly sealed as possible (including keeping the windows closed), or they will be trying to filter all the air in the surrounding region.
More securely attached dirt on finished surfaces in good condition may be removed with surfactants which are mixed in a dilute solution (1-2%) with distilled or de-ionized water. Common types are Orvus Liquid, Igepal, and Triton X-100. If a local source can not be found, surfactants can be ordered from Conservation Materials, 1165 Marietta Way, Sparks, NV 89431, 702-331-0588. A small spot in an obscure area is tested with the solution on a cotton swab. All areas that appear to be a different surface coating or material must be tested separately. If the solution does not damage the test area, it can be used to clean the piece. A soft cloth is dampened slightly and rubbed over the surface. Avoid excessive wetting of the surface, which may cause the types of damage associated with water. The cleaned surface should be wiped with a soft cloth dampened slightly with plain distilled or deionized water to remove surfactant residues, followed by a dry soft cloth. Finished surfaces that show deterioration or bare wood should not be cleaned with water solutions of surfactants and should be referred to a conservator.
Finishes do not require any treatment to help preserve them other than provision of good environmental conditions. Polishes do not prevent finish deterioration. At best, they visually compensate for degradation that has already occurred and at worst, they rapidly accelerate finish deterioration.
Oils in furniture polishes are of two types, those that dry chemically and are responsible for blackening of the surfaces of objects on which they are used, and those that do not dry, remaining oily and entrapping dust. Concurrently, as drying oils oxidize, they become very difficult to remove. Additionally, many polishes contain silicones and other additives than can cause future finish adhesion problems. Manufacturers are not required to disclose the contents of their products, so there is no way to judge their long-term effect on collection objects. Finally, contrary to advertising claims, these proprietary surface applications do very little to protect surfaces and prevent deterioration. They do not prevent dryness or "nourish" the wood. The temporary improvement in appearance is not worth the risk of potential damage. For these reasons, furniture polishes should not be used on collection items.
The major exception to this is some degree of protection provided by wax from water damage for pieces that are in use. Even so, aesthetic enhancement is the major reason to apply waxes to collection items. Properly applied, paste waxes can raise slightly the gloss of the finish, even finish irregularities somewhat and increase the saturation and depth of color of the wood. Unlike oils, they are removable in the future.
If waxing is chosen as an option, use only high quality paste wax such as Butcher's, Minwax, or Renaissance. Reapply wax no more often than every 1-10 years, in spite of more frequent application recommendations printed on their cans. Generally, between applications, buffing with a soft cloth will restore the lustre.
Avoid any product that contains silicones, as they are nearly impossible to remove from the surface once applied and will interfere with future treatment attempts by prohibiting the bonding of coatings and finishes. Generally, silicones are present in spray and liquid polishes, even those that are called "waxes".
Nicks and Scratches
It is best to consult with a conservator before attempting treatment of furniture nicks and scratches. Improper treatment of this type of damage can greatly increase of the complexity and cost of "undoing" a poorly done job. If conservation consultation is not available, limit your treatment only to the specific damaged area. Do not let your work extend beyond the edges of the scratch or nick.
Many nicks or scratches are obtrusive primarily because the finish has been disrupted and the wood surface is no longer optically saturated. In-finishing the damage with shellac or Acryloid B-72 using a very fine tipped artist's brush often will acceptably hide the disfigurement.
If this is not successful, application of color may be required. Utilize artists' acrylic paints on fine artists' brushes. Different colors can be mixed to produce the best color match with the damaged area. As acrylics dry to a matte appearance, gloss can be increased by topcoating with shellac or Acryloid B-72 (Acryloids and reversible acrylic paints are available from Conservation Materials and other suppliers). Another coloring option is to mix dry artist's pigments directly in shellac or B-72 and apply them in the same manner as acrylic paints.
Do not expect to produce an completely invisible in-finishing or in-painting job. If your work is not obtrusive to the average visitor at the normal viewing distance, you have been successful. Remember, you will always see your repair, since you know exactly where to look.
Polishing of brass and silver hardware, even with the mildest of agents, removes some of the surface metal. After repeated polishings, surface decorations and details can be lost and plated surfaces removed to the base metal. If the polish is not removed completely, residues can act as sites for corrosion of the metal. Additionally, in the art historical community, there is an ongoing debate on the desirability of shiny furniture hardware.
If you choose to polish, remove the hardware from the piece, being sure to note the exact location of each screw and nut. Polishing hardware on the piece abrades the surrounding finish and allows polishing agents to run beneath the hardware where they can damage the metal and the finish. After polishing with any good metal polish, thoroughly remove all residues by rinsing in acetone. Gloves must be worn when handling hardware to prevent fingerprinting. Latex surgical gloves, available at drug stores, work well. Coat the hardware with Acryloid B-72 for pieces that are not used or handled, or with Incralac or Acryloid B-48N for pieces that will receive occasional use. These coatings will prolong greatly the time between polishings, perhaps for as long as 50 years, and they are reversible, allowing removal and repolishing in the future.
Since the emergence of the profession of furniture conservation has only been within the last few decades, there remains a myriad of mis-information on deterioration and care available to the owner of historic furniture and wooden objects. It abounds in books and articles, and is pronounced in an especially articulate and misleading manner from the mouths of demi-experts. Dispelling these myths and untruths is extremely difficult.
Myth #1: "Wood is alive." Wood is not alive. Even in the living tree, the vast majority of wood cells are dead. When the tree is cut, the few remaining living cells die. By the time furniture is made from lumber cut from trees, the wood has been dead for a long time.
Myth #2: "Wood needs to breathe and applying coatings such as waxes suffocates it." Wood does not breathe. There is no need to have free air circulation at the surface of wood and coating wood with finishes will not cause damage to the wood.
Myth #3: "Wood and finishes need to be fed." Wood and finishes do not need to be fed or nourished. Wood is not alive and therefore, can not need food. Wood that is unfinished or existing finishes that are dirty and somewhat deteriorated appear dry and "lifeless." The optical saturation and depth of colors characteristic of a freshly-applied finish is not present. This is purely a visual phenomenon and does not indicate that the wood is deteriorated or in need of sustenance. If aesthetic enhancement is desired (it is not required for preservation), unfinished wood can have a reversible finish applied and existing finishes can be cleaned and waxed.
Myth #4: "As wood ages, it loses moisture and natural wood oils, which need to be periodically replaced (usually with the favorite oil polish or feeder of the expounder)." Most woods do not have oils. Of the few that do, the oils in no way affect the preservation of the wood and adding oil (which, as a matter of fact, is not the same oil as that present in the wood) will not have positive effects on preservation, as described above. The amount of moisture in wood is directly controlled by the relative humidity and temperature of the surrounding air. Wood can not lose moisture if it is at equilibrium moisture content with the ambient environment unless the relative humidity falls. Adding moisture to wood in an attempt to replace that which has been "lost" will cause a temporary rise in moisture content which will immediately begin to fall until it again reaches equilibrium with the environment. This rapid moisture content rise and fall may cause damage to the wood in the form of compression setting and splitting. Certain proponents of oil polishes claim that the oil itself replaces moisture lost from wood. This is blatantly incorrect. Oil can not enter the cellular structure to substitute for water; in fact, oil is hydrophobic and is repelled by water
Choosing a Conservator
Currently, there are no licensing or certifications requirements in the conservation profession. Anyone, regardless of knowledge, training, or skills, can call themselves a conservator. Unfortunately, discerning a true professional conservator from a pretender can be very difficult.
Conservators should exhibit a courteous, professional attitude. The conservator should listen to your needs and provide several options to solve the furniture's problems. Be wary of anyone who is pushy about a single solution without having solid facts to back it up. You should receive straightforward information from the conservator, no talk of magic or secret formulas. If you hear about living, breathing, hungry wood - run! The conservator should adhere to the AIC Code of Ethics or a similar ethical code. A condition report and proposed treatment report should be received before any conservation treatment is begun. These documents outline the nature and location of deterioration and the specific materials and techniques that will be used to remedy the problems. Included should be an estimate of cost. Following treatment, a treatment report should be submitted, listing in detail the materials and processes used on the piece during treatment. Photographs of the piece before and after treatment should be provided, including close-ups of specific areas of deterioration. A brochure, available from AIC, entitled "Guidelines for Selecting a Conservator" provides additional helpful information.
There are no easy solutions to choosing a conservator. It requires you to have basic
knowledge and education in conservation issues. The problem of poor treatment of historic
objects has been with society for centuries. In the words of Thomas Hoving in the June,
1987 issue of Connoisseur, "...there's nothing like continuing publicity to keep conservators
on their toes and accountable. In the past, 'restorers' have quietly wrecked more monuments
than Genghis Kahn did." Understanding of proper conservation and maintenance needs can
help prevent this needless loss of our cultural heritage.
Marc A. Williams is President of American Conservation Consortium, Ltd, a firm providing nationwide conservation assessments, collections surveys, and treatment of wooden objects, furniture and horse-drawn vehicles. He is the former Chief Wooden Objects Conservator of the Smithsonian Institution and received his masters degree in conservation from the Winterthur Museum Program. He can be reached at: American Conservation Consortium, Ltd., 85 North Road, Fremont, NH 03044, 603-679-8307.
American Conservation Consortium. Ltd.
4 Rockville Road, Broad Brook, CT 06016, 860-386-6058, firstname.lastname@example.org
Copyright 2008, American Conservation
Consortium, Ltd., all rights reserved