One of the key standards of preservation is that of reversibility: anything done to preserve a piece should be able to be undone with minimal damage to the piece itself. Because wet cleaning is a chemical process, it is not reversible, and so should be used only when absolutely necessary. Before cleaning a textile, certain questions should be asked to determine both the best treatment for that particular combination of textile and soil, and to ascertain whether the piece is able to be cleaned, or may sustain damage during the process. What is the chemical composition of the textile? In other words, does it have a high acid content? Where there chemicals used in its production that might contribute to how it reacts to water? Or how it may react to cleaning chemicals? What are the characteristics of the fibres? For instance, cotton and linen, being plant fibers, are both stronger wet than dry, and so may be able to withstand a more mechanical stress than something like silk. Wool can absorb large amounts of water, but mats if washed in high temperatures. All silks become brittle with age, but weighted silks (see Textile Instability above) decay more quickly, and thus must be handled with extreme care . Additionally, some silks, once wet, can be permanently spotted. Learn the basic characteristics of the type of fibres you have, and how they have been treated before undertaking any kind of cleaning. What colourants have been used, and how will they react to cleaning? This can apply not only to dyes but to mordants as well. Different parts of the world may have different dye processes, so here is where knowledge of when and where a textile originated, as well as a working knowledge of chemistry, can come in handy. If in doubt as to the wash ability of a dye, apply a drop or two of water to an inconspicuous place and blot with a clean white cloth. If the dye transfers to the cloth, even in small amounts, the textile should not be washed [18]. Are there finishes or surface treatments that must be preserved? For example, is the fabric painted? If so, it should never be washed; some other cleaning method should be used. What kinds of soils are there? The older the stain, the more difficult it is to remove. After a certain point, it may be best to leave the stain or soil, or remove it only partially, in order to preserve the rest of the piece. Additionally, soils which may not be detectable to the naked eye might be present in the textile; flags, for instance, may be highly acidic due to long exposure to air pollutants, and should be treated by a professional conservator . What cleaner is safest and most effective? Commercial detergents should never be used on antique textiles, whatever their claims of gentleness: the chemicals used in most clothes detergents are too harsh for old fibres to withstand. A wide range of speciality detergents are available from conservation suppliers, though most sources suggest Ivory dish soap as a last-minute substitution if needed. Never use chemical spot cleaners, as they are likewise too harsh for old fibres to tolerate. This is especially important for pieces in situ, as this may endanger other nearby pieces as well (the wooden part of an upholstered piece of furniture, for instance) . What additives and cleaning aids are needed? This can include physical supplies (water, screens, a vacuum cleaner), as well as chemical (water softener, cleaning agents, etc.). How long can the specimen be exposed to the cleaner? Prolonged exposure may cause additional damage to the fibres. What mechanical action can be used? The older and more fragile a textile, the less movement it will be able to tolerate during the cleaning process, so this should be considered before undertaking a cleaning. Once the best cleaning process has been determined, the piece should be prepared for washing. Usually, this involves vacuuming to remove any surface dirt. Linings and backing should also be removed, vacuumed, and washed separately. This is not only to prevent colour bleeding, but to avoid trapping dirt between the layers, which may cause discolouration from the inside. Additionally, different fibres react differently to cleaning, and fabrics may shrink or stretch, which, if still attached together, may cause rippling and distortion in the lining and outer layer of the textile [16]. As with moving or working with dry pieces, the textile should be washed in a flat, fully supported position. Usually this is achieved through the use of screens like the ones used in vacuuming, though these may be supported in a frame of some kind for added stability. The textile should be sandwiched between two screens. If the piece is particularly delicate or fragile, it may be wrapped in netting, then placed between the screens [16]. The cleaning solution should be prepared using distilled water. If that is unavailable, softened water may be substituted. The main concern is to avoid hard water, which will leave deposits of minerals in the fibres [18]. The solution should be placed in a container large enough for the textile to lie flat in. For large pieces, it may be necessary to construct a temporary basin outside or in a large room: Putnam and Finch suggest using boards or bricks to constrict a frame, then lining it with a large piece of plastic, weighted on the sides, and strong enough to support the water that will be poured into it. If a smaller basin is used, it should be of ceramic, stainless steel or a stable plastic. The screen-encased textile is lowered into the solution. The textile can then be washed by pressing a soft sponge directly down onto the fibres. DO NOT RUB the sponge, as this will cause unnecessary abrasion at a moment when the textile is already weak from the water [21]. The textile may be submerged for no more than an hour, and should be rinsed at least four times after it is cleaned (Mailand). The final rinse should always be with distilled water. The textile should be placed to dry on a flat surface or screen, in a well-ventilated room away from heat.
