THE DISEASES OF THE L. — Numerous agents of a physical and biological nature can more or less profoundly modify the structure of writing material, producing alterations that may resemble diseases, owing to certain affinities with the morbid conditions proper to plant and animal organisms. Their onset may be prevented by suitable prophylaxis, or their progress and development may be arrested by promptly applying remedies appropriate to the nature of the processes to be combated.
Climatic factors—that is, the combination of conditions of humidity, temperature, pressure, ventilation, and insolation—may by themselves cause such alterations if they exceed certain maxima or minima, or may encourage the spread of harmful biological species. When climate is discussed, reference is made to that of the environment in which the l. are preserved, not to one of its agents alone but to all of them and to their mutual relationships. To ensure that library material remains in a hygienic state of preservation, the average temperature must not exceed 18° or 20° C., provided that relative humidity does not fall below 40% or exceed 65%. Beyond these limits, fibres, fabrics, and adhesive bindings suffer from excessive or insufficient humidity. The same occurs with permanent imbalances in the other factors. Insects, moulds, and bacteria live and reproduce more easily when they encounter thermal and hygrometric coefficients higher than the averages indicated above.
Thus a tradition of study has gradually developed in which the causes, genesis, and pathological manifestations are investigated, as well as the means suitable for preventing and combating them. Among the biological agents, the first place belongs to man, who, as the maker or user of the l., consciously or unconsciously causes it potential or actual, direct or indirect damage. From remote times there has been information about voracious insects that damage l. and shelves. Only, however, since it became possible to distinguish one species from another, to study their habits and biological capacities, have prophylactic measures been adopted to prevent their spread; and, in cases of infestation, interventions have been devised capable of ensuring energetic and rapid extermination.
Almost all alterations of a microbial nature (pigmentation, downy and granular growths of various colours, etc.) are collectively referred to as moulds. Many of them are in fact due to the specific action of fungi, sometimes merely chromogenic and sometimes cellulolytic, but which, according to current thinking, presupposes bacterial action as a preparatory or concomitant factor. Some species are exclusively paper-dwelling, while others are ubiquitous. Their fibrolytic activity also varies. Parasitologists and hygienists have devoted particular attention to the spread of pathogenic germs by means of the l. and to its contagiousness among readers, without, however, reaching concordant and definitive conclusions. The l. may suffer damage from violent traumatic causes as a result of accidents: fires, collapses, volcanic and alluvial catastrophes, explosions, and shipwrecks. These result in oxidation, carbonization, crushing, abrasion, pulping, and dilution.
Once the nature, causes, and genesis of the damage have been established, with the aid of the necessary experimental means, the material is treated in such a way as to halt the degenerative processes under way and, through restorative interventions, to ensure its continued preservation. Preliminary investigations are therefore required to identify the agents that produced the alterations, together with research into the selection of remedies to be employed: pest-control agents and antiseptics, decolourizing reagents, cleansing actions and substances, and the possibility of total or partial intervention.
Restoration consists of a complex of operations requiring special techniques. It derives from an ancient craft tradition that liked to surround itself with mysterious secrets. Today, thanks to the progress achieved and to the collaboration of experimenters, rational procedures have replaced customary empiricism. Taking rigorous account of the particular condition of the material, restoration may be total or partial. It must purify the material, not the writing, ornamentation, or any mark left upon it by the hand of man. It demands the greatest sense of responsibility and the most absolute and vigilant respect for the morphological and structural integrity of the various elements composing the l. It must in any case be regarded as an exceptional remedy, to be adopted only in cases where the preservation of a text is seriously compromised. The restoration operations subsequently carried out are: a) unsewing of the l.; b) cleaning, stain removal, and washing of the individual leaves; c) patching; d) flattening; e) recomposition and sewing; f) rebinding and finishing. — Vedi tav. LXXXV.