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The Museum Conservation Institute- Taking Care


We provide information so you can learn how to preserve stuff

Mold and Mildew

  • Source
    Textiles made from natural fibers are hygroscopic -- they absorb water or moisture very quickly and desorb it (dry out) very slowly. High humidity, warm temperatures, and poor ventilation encourage mold growth. Microscopic spores of fungi and bacteria are always present in the air. Generally, stagnant air above 80% relative humidity (RH) will support mold on cellulosics -- cotton or linen. Above 92% RH, on wool and silk will be affected. Soiling, organic residues, and stains from the indiscriminate handling of textiles will enhance the growth of mildew on fabrics at lower relative humidities. Humid air that is cooled but not dehumidified will have a very high relative humidity.

  • Immediate Treatment
    Remove the affected textiles from the damaging environment by supporting them with the existing (even damaged) boxes or cardboard. Spread the textiles carefully upon clean, absorbent, dry surfaces. Allow the textiles to dry. Use fans to increase the air circulation in the vicinity of the objects, do not focus fans directly upon the weakened, mildewed textiles. For single objects, a hair dryer at low temperature may be effective. Do not use an oven or microwave!

  • Treatment
    Review the previous storage or display area for structural defects (inadequate insulation, damage to pipes, flooring, ceiling). Review the rate of air circulation. Improvement in air circulation can be achieved four ways: by installing fans, by installing dehumidifiers, by installing air-conditioners (if they lower the relative humidity as well as the temperature), or by raising the temperature to lower the relative humidity. Once the mildew has dried, the residues of mildew can be removed by gentle vacuuming action with a HEPA filtered vacuum cleaner. Test the technique, the vacuum suction pressure, the effect of the brush on a small trial area of the fabric. A soft brush may be used to loosen the residue, if the fabric beneath is sufficiently strong. Washing or dry cleaning is not recommended.

  • Musty Odors
    Musty odors are caused by volatile components of the fungi or bacteria. Warm dry airing of the textiles will promote the dissipation of the smell. Commercial products contain ethanol (alcohol) and hydrophobic/hydrophilic compounds that tie up the odor producing chemicals. While these commercial products will not harm the fibers, they may affect dyes and finishes, causing bleeding or loss of sheen.
  • Stains & Spots
    Some fungi and some bacteria produce colors as they grow. These may attach tenaciously to the fibers. Zerophilic fungi produce rust-colored spots. Often seen on the pages of old books or antique linens, these freckle like spots called 'foxing' are the result of a melanin type exudate, not rust. Oxidative bleaching with hydrogen peroxide may reduce the color but will further weaken the cloth or paper.

  • Cautionary Note
    The portion of the textile that is obscured by mildew is weaker than the unaffected areas. Chemical treatment ("wet-side spotting") may be deleterious to the fabric, to the dyestuff, and/or to the finish. If the growth has damaged enough fiber surface, removing the growth will reveal a perceptively damaged--and perhaps discolored area. Radical treatment may only abrade this surface more; washing and agitation may increase the likelihood of rips, tears, and holes.

  • Prevention
    Geographical, climatic factors should be considered. In some areas of the country, seasonal changes can adversely affect the conditions in the storage or display area proposed. Because of their hygroscopic nature, textiles can be damaged by spikes of high humidity. Monitor the area chosen periodically to check the temperature and humidity levels. Attics, basements, closets against exterior walls are places susceptible to changes in temperature and hence to changes in relative humidity. They are not recommended for textile storage.

  • Antifungal agents
    Textiles and carpets known to be subject to adverse/problematic conditions (summer storage of rugs) may be rolled and surrounded with p-dichloro-benzene (PDB mothballs), interleaved with muslin or tissue. Cellulosics may be stored with thymol or eugenol (oil of cloves). These agents sublime from the solid state to the gas phase. The volatile, gaseous state--what one smells--is what acts to prevent mold growth.

    However, these agents may damage some dyes, do cause discoloration of plexiglas, and are deleterious to human health. Thus, if these anti-mildew agents are used, the dry objects should be stored in sealed, closed, air tight containers like metal, waterproof trunks and well aired before use or display.

  • Safety
    People with asthma, chronic pulmonary problems or immune compromised conditions should consult their physicians before working with mildewed textiles. The microbes affecting textiles are not generally pathogenic, but the large quantity of spores can affect health. Gloves, goggles, and fit-tested filtered, rated facepieces should be worn while handling mildewed objects. Protective gear should be thoroughly cleaned and sanitized after each use--or bagged and discarded. Clothing worn during the handling of mildewed textiles should be laundered with hot water, well rinsed, and, of course, thoroughly dried.

To see a translation in Estonian.

Updated: September 2006; 2012

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