Among the varied causes of deterioration of art works is biotic infestation; that is, the infestation by living organisms. In paintings with wood or textile supports these organisms are essentially fungi (mold and mildew), bacteria and insects. In the majority of the situations, the phenomenon is closely tied to abiotic factors, and in particular, to the presence of humidity. In all cases, humidity favors the development and the promulgation of biotic infestation. Scarce attention paid to the conservation conditions in which the work is exhibited or stored is often at the base of very serious deterioration. This can also be said for those situations that contribute to a possible total destruction of the object , as in the case of attack by rodents such as rats and mice.
Mold consists of microscopic fungi that develop and feed on organic materials. Many of the materials that make up paintings on wood panel and canvas offer the perfect conditions for the development of these organisms. Animal glues, wood, starch, vegetable fiber and skins are the materials that are most subject to this type of risk. An environmental relative humidity that is over 60-70%, scarce ambient light, temperature above 15 °C and the presence of stagnant air are the conditions that favor the diffusion of microorganisms. In addition, the fact that a painted surface is not flat favors the adherence of spores that can cause spotting, color alterations and changes in the mechanical characteristics.
The presence of mold and mildew can be seen due to the fact that there are white, grey or black filaments attached to the structure of the material. The resulting alterations of the object differ in type. In the case of wood, these alterations can lead to a decay called rot. In general, when the lignin and the cellulose are attacked and destroyed, it is known as white rot; brown rot occurs when only the cellulose of the wood is the victim.
Bacteria can also cause deterioration similar to that caused by wood-decaying fungi. An example is seen with the presence of Streptomyces that have a cellulolytic action. Even in this case, humidity is instrumental in the diffusion of the bacteria. Nevertheless, in order to develop, bacteria must have a particularly high level of water in the material itself. For this reason, the phenomenon is usually limited to archaeological objects that have been in contact for long periods with the ground and decaying materials.
Nevertheless, the most damage is caused by insects, and particularly those that breed and feed on wood supports. These insects get nourishment from the quantities of starches, sugars, proteins and vitamins in the wood. In this case, the hylophagus insects bore deep channels in the wood. In the most serious cases, they transform the wood into a very porous and friable material. The species that are capable of causing this type of extensive damage is fairly limited, and their diffusion is dependent upon climatic conditions and the type of wood. In essence, the damages that can be connected with historic-artistic heritage are hylophagous insects belonging to the order of Coleoptera and that of Isoptera.
The order of Coleoptera is made up of various species of insects. They are winged, with shape, color, and size quite variable. Their reproductive potential is usually quite high. This capacity is for reproduction is increased in warm climates or in heated environments. The most widespread species are limited to a few families, among which are the Lyctidae, the Cerambycidae (the long-horn beetle belongs to this family) and the Anobiidae. The species of this latter family – usually referred to as furniture beetles (wood worms, Nicobium castaneum, Xestobium rufovillosum, Ptilinus pectincornis) – are particularly widespread. In the larval state they feed on substances in the wood. The channels and galleries they create cause serious damage from both a structural and aesthetic point of view. They attach both gymnosperm and angiosperm wood. Therefore, it is possible to find them in all wood supports for paintings. Most often the greatest area of infestation and damage can be found where there is the presence of glue, especially at the joints of the panels and in the priming layers.
Compared to the Coleoptera, the order of Isoptera – commonly known as termites – is even more fearsome. They shun light, and it is difficult to distinguish their presence by simply looking at the exterior of the wood. The result is that the wood can already have undergone an attack and be quite weakened, even though it looks whole. They live in communities often made up of millions of individuals and their infestation is helped along by warm, humid environments. For example, in Italy termite attacks have been frequently found in the central-southern areas. Most common here is the family Kalotermes flavicollis and Reticulitermes lucifugus.
Manfredi Faldi – Claudio Paolini
Estratto da: Artis (Art and Restoration Techniques Interactive Studio), Direzione scientifica: Manfredi Faldi, Claudio Paolini. Cd Rom realizzato da un gruppo di istituti di restauro europei, coordinati dall?Istituto per l?Arte e il Restauro Palazzo Spinelli, con il determinante contributo della Commissione Europea nell’ambito del programma d’azione INFO2000.
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