2023-05-01 22:29:12
The heart of the Dordogne region of France is home to the most impressive display of prehistoric art. For centuries it remained hidden in the Lascaux cave. It was discovered by four young men in 1940 and is a jewel belonging to the late Aurignacian (15,000 to 13,000 BC).
The main cavern and several connected galleries are decorated with some 600 paintings of animals, some imaginary, made with mineral pigments mixed with animal fat in various shades of yellow, red, brown and black. It is so spectacular that it has been nicknamed the “Sistine Chapel of the Paleolithic”. In 1948 the Lascaux cave was opened to visitors, but in 1963 it was closed indefinitely to the public. The closure was imposed by the discovery of a green patina that covered the painted parts and that was composed exclusively of the unicellular algae Bracteacoccus minor.
Unfortunately, the isolation has not been enough to stop the deterioration of the paintings. In 2001 multiple white spots appeared on the paints due to the fungus Fusarium solani. And soon it was followed by large black spots caused by another fungus, Scolecobasidium lascauxense. To top it off, in the last 15 years the so-called “dark zone” has emerged in the apse room, attributed to various fungi and bacteria.
art is not sterile
The Lascaux rock art is just one more victim of biodeterioration, that is, undesirable changes in a material caused by the vital activities of organisms. Bacteria, archaea, fungi, microalgae and lichens, as well as many species of insects and other animals, constantly cause problems in the conservation of cultural heritage.
In the case of caves, the human presence unbalances the native microbiota –anthropization–, damaging the rocky surface and Paleolithic works of art. Sometimes it is the fault of actinobacteria and ascomycetes. Others are due to the proliferation of cyanobacteria and chlorophytes, associated with artificial light systems, which cause the so-called “green disease”.
The development of a calcite veil that masks the paintings on the walls is also common, and usually involves bacterial genera such as Pseudomonas, Bacillus y Myxococcus. Or the appearance of white, yellow, gray, black or red spots attributed to the growth of different bacteria and fungi. In the Altamira cave, for example, the gray and yellow spots seem to be caused by a combination of up to six different families of bacteria.
Beyond caves, microorganisms can cause serious aesthetic destruction to paintings, textiles, ceramics, mummies, books, manuscripts, and many other objects. The most common superficial damage includes pigment discoloration and the appearance of unwanted organic pigments. Other times the deterioration is less visible, because it affects the interior of the pieces, which can end up shattered due to acid corrosion, enzymatic degradation and mechanical attack.
Continuing with the specific examples, in the Italian region of Campania, which has a great wealth of ancient paintings and is home to priceless frescoes, the most frequent species isolated from wall paintings include bacteria of a wide variety of genera such as Alcaligenes, Arthrobacter, Bacillus, Paenibacillus, Flavobacterium, Pseudomonas, Micrococcus, Staphylococcus, Nocardia, Mycobacterium y Task.
The stone is not safe either
Stone is by no means immune to microbial attack. Proof of this is the tremendous biological deterioration that the ancient structures of Angkor (Cambodia) are suffering. In particular, the Bayon temple, known for its intricately carved bas-reliefs, is being lost due to exfoliation and the formation of biofilms, which are multi-colored microbial layers formed on the surface of stone.
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This situation is also damaging historic cathedrals and churches in Europe. In fact, on the continent they are concerned about the biodeterioration of stained glass windows, due to the growth and/or metabolic activities of microscopic fungi, bacteria and lichens that can accelerate the physical-chemical processes that lead to glass breakage.
The good news is that there are microorganisms that can counteract this damage. Without going any further, restaurateurs are using bacteria from the genera Bacillus, Sporosarcina y Myxococcus to actively bioinduce calcite precipitation and reinforce monumental stone.
As many visitors in museums as in airports
On many occasions, international human traffic inside museums is similar to that developed in the busiest airports. To give one example, in 2019 there were almost the same number of visitors (approximately 28 million) for the top five London museums combined (British Museum, Tate Modern, National Gallery, Natural History Museum, Victoria & Albert Museum) as for London Stansted Airport. Although culturally it is a good sign, this movement of people also causes a strong flow of microorganisms capable of attacking works of art.
In museums and collections, as well as in libraries, fungi (Aspergillus, Paecilomyces, Chrysosporium, Penicillium y Cladosporium, etc.) play an important role in the biodeterioration of documents made of paper. The activity of microorganisms can cause the formation of brown or reddish spots on the paper, known as foxing.
The fungal biodegradation of wood is also significant, because there are objects made of wood that contain important information about ancient cultures. Fungi, especially those that cause white, brown, and soft rot, can easily penetrate and degrade wood.
As for historical textiles, they are usually made of natural organic vegetable fibers (cotton, linen, hemp and jute), or animal fibers (wool, silk or leather). All of them an attractive morsel for microorganisms.
When the target of microorganisms are historical photographs and motion pictures, several problems arise. On the one hand, the image loses sharpness. But in addition, gelatin, a binder used mainly in the 19th century to create positives and negatives, is easily colonized and degraded by microorganisms with proteolytic properties, such as Bacillus, Clostridium, Micrococcus, Enterococcus, Pseudomonas, Staphylococcus, Streptococcusetc.
Can all these damages be prevented? Without a doubt, yes. On the one hand, controlling the temperature and light, among other aspects. In addition, routine monitoring is convenient. Nor should we forget that dust usually carries a large number of bacteria, fungal spores and potential nutrients for microorganisms, so frequent cleaning is an important preventive action to avoid biological damage to historical objects.
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