| Prevention and treatment of mold in library collections with an emphasis on tropical climates: A RAMP study |
|3. Implications for library materials|
|3.1 Vulnerability of materials|
In order to prevent mold growth, or to treat it effectively once it has developed, it is not necessary to identify which of the thousands of genera of mold may be involved. It is however necessary to understand the basic structure of the mold organism and the manner in which it takes advantage of favorable conditions. This means that librarians must assume responsibility for a wide range of knowledge concerning the materials in their collections as well as the nature of the threat in order to make informed decisions regarding appropriate treatments.
In 1940, Beckwith and his co-workers isolated 55 different mold cultures from old book papers, including eleven genera, of which Penicillium and Aspergillus were the most commonly found.1 In the study, spores were removed from the papers, transfered to a culture medium and grown under laboratory conditions. This is not to say that all of them would have been able to use the paper as a medium for growth, but certainly some of the strains of Aspergillus and Penicillium would be likely to attack cellulose or one of the numerous paper additives, sizes, fillers or coatings. At least 180 genera or species of mold are known cellulose destroyers, i.e., they use the cellulose fiber as a nutrient.2
Other molds that do not actually consume cellulose may damage paper by weakening the fiber bonding as they feed on other materials in the paper. The fillers, sizes and coatings added to the paper during manufacture to improve printability, texture, color or brightness are a potential source of nutrients, and may include starch, gelatine and casein. Rosin size was found by Beckwith to inhibit fungal growth;3 however, rosin is acidic and has been found to accelerate the chemical deterioration of paper and its presence is not cause for rejoicing. Very little is know about the various synthetic sizes, as much of the research in this area took place before they were in common use.
Paper in bound volumes is less vulnerable to high ambient relative humidity than unbound paper. Cryptogamic fungi seldom occur in closed volumes under such conditions, but rather on the bindings and on unbound sheets of paper exposed during prolonged periods of dampness. Foxing, on the other hand is commonly found in text blocks.
In cases of flood or other severe wetting, book paper may be considered to be more vulnerable, since the bulk of the volume and the compression of the paper at the spine slow the drying process considerably.
Many bookcloths, including those of cotton and linen, are cellulosic and are vulnerable to the same range of mold species that affect paper. Like paper, the fillers and coatings added during manufacture provide an additional source of nutrients. The unsized cloth frequently used in bindings from India and Southeast Asia is particularly vulnerable. Because it is often quite thin, the adhesive used in attaching the cloth to the boards often penetrates the weave of the cloth, allowing mold to grow on the surface. Starch filled buckram, commonly used in more temperate climates is also an excellent source of nutrients. Manmade fibers, or natural fibers coated with synthetic resins, i.e., peroxylin cloth and acrylic coated buckram are more resistant to mold, but not entirely immune. No literature was found regarding the affect of dyes on mold growth, although dye. have been found to have considerable effect on the resistance of textiles to photochemical action (some accelerating deterioration and others providing protection).4
Tanned leather is more resistant to mold growth than untanned leather. Chrome tanned leathers are relatively impervious, vegetable tanned leathers considerably less so. Book leathers are, unfortunately, vegetable tanned, chrome leathers being used primarily in shoes, luggage and other such items.
Studies indicate that mold growth does not affect leather in the same way that it does cellulose. The mold apparently does not attack the hide-tannin complex itself.
Barghoorn has demonstrated that invasion and destruction of the collagen aggregates of the hide substance does not occur; and Hyde, Musgrave and Mitton have shown that vegetable-tanned leathers suffer surprisingly little damage through even fairly heavy and prolonged mold growth. Experimental evidence indicates that the major cause of tropical deterioration of leather is hydrolytic breakdown due to the high atmospheric humidity and temperature and to their effect on interfiber lubrication, the extent of the hydrolysis being dependent upon the pH of the leather.5
Thus, it seems that the components of leather which support mold growth are the lubricants, the conditioning materials and the finish. It would seem from the literature cited above that high ambient relative humidity rather than mold damage is the primary cause of deterioration of leather in tropical climates.
Oiling of leathers, which many libraries have viewed primarily as a cosmetic treatment, may in fact be the most viable way of protecting leather in a tropical environment. Some libraries in tropical climates have avoided leather dressings, fearing that the use of oils and lubricants would promote mold growth. However, since any resultant mold growth is superficial and causes no structural damage to the leather, and since the application of a leather dressing prevents the hydrolytic damage that is the chief cause of deterioration, the use of leather dressings of appropriate composition should be considered beneficial.
With regard to the choice of a particular leather dressing, experience in the tropics indicates that a very light coat of neatsfoot oil and lanolin, allowed to dry for 24 hours and then buffed with a soft cloth works well. Leather dressings containing wax, including one developed by the British Museum, do not harden satisfactorily in warm humid climates, and the surfaces of treated items tended to stick together when returned to the stacks.
Pastes (made from vegetable starches), glues (made from animal products) and gums (made from vegetable resins) are all subject to mold growth to varying degrees. The use of excessive amounts of adhesives may be one factor in promoting the growth of mold. With regard to the application of adhesives, more in not necessarily better.
Synthetic adhesives, including polyvinyl acetate emulsions (the so called "white glues" which vary enormously in composition and properties), pressure sensitive adhesives on tapes and labels, heat set adhesives such as those used in dry mount papers, and aerosol spray adhesives are more resistant to mold, but not entirely immune. They are solvent based, and therefore dry quickly. However, their poor aging properties and the fact that solvents are required for their removal make them undesireable for the repair of torn or damaged paper.
Despite the possibility of mold, pastes and gums are recommended for mending of paper due to their reversability. Proper application and thorough drying of the adhesive film provided the best protection. Repairs to bindings are perhaps best done with good quality PVA.
All photographic materials have in common a substrate of gelatin which carries the emulsion of silver halide particles that produce the image. The film base may be nitrate, acetate, polyester, glass or paper and the format may be a negative, a photograph, or a reel of microfilm, but all have a gelatin layer. As with the gelatin sizes used in paper, photographic gelatin provides a nutrient for mold growth, which can penetrate the emulsion layer, damaging the image. The polymers that provide the base for contemporary film stock are generally very resistant to fungal attack,6 however paper and glass supports are both vulnerable. Glass plate negatives can actually be etched by fungi, and combined with the damage to the silver halide layer, can render the negative completely useless.
Gelatin is relatively stable as long as it is kept dry. In high humidities gelatin begins to swell and if exposure is prolonged, becomes sticky. This can occur at relative humidities as low as 60%.7