Importance Of Cultural Degradation

Cultural Heritage's bio-degradation

Cultural valuable objects correspond to a large variety of raw materials: stone, clay, wood, pigments, mortar, metal, etc... None of them is immune to decay, also known as degradation. Due to the objects' significance for local and international communities, it is of prime importance to understand their decay and help preserve them.

Although, materials' degradation involves numerous parameters, it is possible to reduce them to two main factors: weathering, and biodegradation. Weathering consists in materials' irreversible breakdown due to the direct contact with its surrounding environment. Humidity, temperature, ventilation, pollution are some aspects that take a crucial role in materials' weathering. They

By their diversity and adaptability, they can colonize, contaminate and alter all substrates. They, then, induce a large variety of alterations. Degradations can be superficial and reversible, but they can also be more problematic by impacting the artefacts in their whole integrity in a serious way, possibly to their entire destruction. They can for example form some degradation products setting up coloured patinas, some acids which dissolve the substrate, induce cracks during their growth... Some of the degradations' compounds they produce can also directly alter the material with which they are in contact, making the microorganisms influence on the materials' decay more complicated. This is why there are different kind of biodegradation, a first separation could be direct and indirect biodeterioration. Direct process means that the microbe is altering chemically or mechanically the material by itself. An indirect one refers to an alteration due to compounds produce by a microorganism during its metabolic cycle. Both indirect and direct are usually happening at the same time co-enhancing themselves the object's

Some authors prefer to separate the physical/mechanical damages from the chemical. Although the damages' processes are different, they come most of the time one with another. For example, cyanobacteria growing on stone surface produce substances, which enhance the stone's disintegration and allow their "hyphae" to penetrate into internal layers, causing mechanical damages to the inner part of the stone. This is why, here, they are considered to be only one kind of alterations. Aesthetic changes often imply a bio-contamination of the artefact, the formation of new compounds on the surface of the material or a major alteration of the compound constituting the artefacts considered. Physico-chemical degradations are changing the structure of the material itself and it covers a large panel of modifications: cracks, oxidation, solubilisation,