One of the most common problems in libraries and archives in humid tropical regions is mold. Mold is a general term given to a wide variety of fungi common to most parts of the world. Mold grows through the propagation of its spores, which are always present in the air waiting for the right opportunity to germinate. Moisture provides the necessary conditions for mold germination. The visible signs of mold result from the "flowering" of the spores into mycelium, the familiar, velvet-like surface covering. The mycelium, in turn, becomes powdery and generates more mold spores that become airborne to continue the cycle. At this point, mold spores can be dangerous, and the treatment of mold-infected material must be handled with care to avoid inhalation. Although not all molds are toxic to humans, it is important to regard all infestations as possibly toxic and take the appropriate precautions (respirator and gloves) when entering an infested area.

It is important to remember that mold is usually the result of high humidity and poor air circulation. Temperature is less of a factor, except, of course, as it affects relative humidity (low temperatures result in moisture condensation on surfaces). Mold can grow on any moist surface, including materials such as paper, leather, and book coverings, causing disfiguring, multicolored stains and greatly reducing the material's strength.

Detecting mold

Mold grows in conditions of high humidity, direct wetting, and poor air circulation. Sometimes mold develops in a small, isolated area within a larger space served by a generally efficient HVAC system. In this case, a survey of the area will usually reveal inadequate air circulation. In some cases, a micro-environment such as an exhibit case can be conditioned to control humidity through means of a desiccant like silica gel, which absorbs moisture and thereby reduces humidity. This approach is only effective in an enclosed system.

Mites known as book lice can be a useful indicator of mold. These tiny grey/white insects inhabit the inner margins of damp books and feed on microscopic mold embedded in the paper. Hidden mold can also be detected with ultraviolet light, exposure to which causes the fungi to turn fluorescent. Mold can also be detected by the musty odor common to damp basements.

If mold is discovered, take immediate steps to discover the cause. Check for water infiltration (wet floors, ceiling, or walls). Is the HVAC functioning correctly? Does it provide the appropriate level of air flow, and are the pre-heat coil and misting unit working? Is there a structural problem causing rising damp or condensation?

Preventing mold

The only way to prevent mold is by altering conditions conducive to its growth. For example, paper collections should not be stored in a basement with a low temperature, high humidity, little light, and very low air circulation—ideal conditions for the growth of mold. Even if remedial treatment is undertaken, the material will quickly deteriorate again if returned to the environment in which the mold first developed.

When the cause has been traced, take immediate steps to remove it. Vacuum or mop up standing water, adjust the HVAC, and/or activate electric fans to speed up the circulation of air. If dehumidifiers are available, they should be employed with both HVAC and fans.

Mold is the prime enemy of film materials, attacking the surface and emulsion. If film is unprocessed and in a moisture-proof container, it is usually safe from mold. However, when the package is broken, mold threads or filaments develop and immediately become apparent when the film is exposed. Film left in a camera in humid conditions is especially susceptible to mold. Coating microfilm during processing is regarded as a useful preventive measure, as this reduces the risk to the emulsion layer and allows the mold to be removed before serious damage occurs. One such coating is polysulfide, developed by the Image Permanence Institute of Rochester, New York (USA).

Treating mold-infected books

In the past, various chemicals were used to "kill" mold spores, including ethylene oxide in a vacuum chamber (now effectively banned because of health concerns) and heated thymol and para-dichlobenzine (now recognized as mostly ineffective). No matter what chemicals were used to kill mold, materials would again become moldy if returned to the same environment.

If a large number of books are wet or damp, freezing is a way of quickly stabilizing the infestation until appropriate treatment can be dispensed.

The treatment of mold-infected books requires that they be taken to a well-ventilated area with electric fans to increase air movement. A good arrangement is to stand the books on edge with the boards slightly opened have a fan blow across them through an open window or to handle the books inside a running fume hood (cupboard). Mold: FacemaskRapidly moving air will dry out the moisture and desiccate the mold spores, rendering them inactive. If necessary, take the books outdoors and place in the sun and a mild breeze for a short time, and if possible, remove the mold outdoors. Ultraviolet rays from the sun will kill mold. In handling infected books, staff should wear HEPA face masks or respirators and plastic or rubber gloves.

Mold: HepavacuumWhen the books are dry, a HEPA filter vacuum cleaner should be used to remove as much of the inactive mold as possible from the covers of the books.

If the library does not have a HEPA filter vacuum, activated dusters (dusters with an electrostatic charge, or containing a mild adhesive) can be used. The dusters should be laid over the infected area and the mold spores gently picked up. This procedure prevents mold spores from being released into the air.

When the soft mold has been removed, the outside of book covers can be wiped with a solution of ethyl alcohol. This acts as a mild solvent to remove some of the outer staining. Care must be taken not to wet the area too much.

The inside of the books can now be examined. In many cases, mold stains will be seen on the inside of the binding, near the joints and at the head and tail. The stains can be gently swabbed with ethyl alcohol, but it is unlikely that they will be completely removed. Although mold stains can be treated with chemical bleach, this is not recommended because bleach can cause the paper to deteriorate rapidly, especially in humid conditions.

Returning treated books

Books should not be returned to their shelf location until the space is declared completely free of mold and the cause identified and rectified. Affected surfaces in the room can be washed down with liquid bleach (Lysol), but this should be completely dry before the room is again occupied.

Following the return of books to the shelf, the room should be inspected periodically to ensure that mold has not returned. HVAC components should be checked, especially in vent areas, and HVAC filters changed on a regular basis. In the absence of HVAC, ensure that air circulation is improved.

What not to do

Unfortunately, there are numerous rough and ready approaches to mold removal that should be avoided. For example: Do not brush off dried-out mold spores. This will launch them into the air where they can be inhaled.

• Do not spray or swab the books with bleach of any kind. This can cause severe damage.
• Do not use a chemical fumigant without checking to see if it is toxic.
• Do not inhale mold spores when cleaning off books, and do not enter a mold-infested area without an approved face mask.

Mold damage to non-book materials

Prints, maps, framed items, and other artwork needs to be handled with great care, as careless vacuuming or dusting can damage fragile surfaces. A useful mold removal method is to place a piece of fiberglass insect screening over the piece, then vacuum through the screen to remove as much of the inactive mold as possible. If you are working outdoors and wearing a respirator, a soft brush may be employed to gently remove the mold. Take care not to grind the spores into the medium or the paper fibers. If framed materials show signs of mold on the inside of the frame enclosure, the artifact should be unframed, treated, and reframed using new matting and a frame that has been thoroughly cleaned and dried.