"Cultural Relics Doctor" - Microorganisms

Cultural relics, as the historical accumulation of human life, are extremely precious and have very important artistic, historical, scientific, military and cultural value.

Among them, stone cultural relics are particularly valuable because of the difficulty of preservation and the many factors that cause damage. There are many types of stone cultural relics, such as tools, buildings, statues, sculptures, etc.

Generally speaking, stone cultural relics are often exposed outdoors for a long time, and they are damaged by wind and rain (especially acid rain), human damage, microbial damage, salt crystals, etc. It is a consensus among countries and regions to properly protect them, and they have already been put into action.

The restoration and protection of stone cultural relics is currently mainly based on chemical coating methods. However, from the previous application practice, there are many problems.

Organic coatings represented by acrylic resin and epoxy resin have a limited service life, relatively high maintenance frequency, and are expensive. In addition, due to different hydrophobicity, they will cause poor transport of salt ions on the surface of cultural relics, which will then precipitate salt crystals and cause damage.

Compared with organic coatings, inorganic coatings represented by zinc (aluminum) stearate and phosphate, as well as lime water, also have shortcomings.

The "shell" they form is incompatible with the original material of the cultural relics. After dissolving, it will even form precipitated salt crystals in the cracks of the stone, which will cause the surface of the original cultural relics to crack.

While microorganisms bring surprises and benefits to human beings, the pace of their development and utilization has never stopped. They have been "seamlessly" integrated into every aspect of people's lives. Look, they are even present in the restoration of cultural relics.

In fact, using microorganisms that can precipitate carbonates to repair stone cultural relics is nothing new.

As early as the 1970s, Frenchman Pierre Adolf used the "bacterial spraying method" to repair the exterior walls of ancient buildings corroded by acid rain. After 15 days of continuous spraying, a new layer of "rock" "grew" on the repaired wall, and even after many years of investigation, it was still as solid as before. The newly grown "rock" is actually calcium carbonate precipitation caused by microorganisms. Because its hardness is greater than that of natural calcium carbonate, it has a significant advantage in corrosion and damage resistance.

Since then, there have been many reports on the use of microorganisms to restore stone cultural relics.

For example, Tiano et al. used Bacillus subtilis to reinforce stone cultural relics in the late 20th century and achieved good results;

Around 2006, Gauri et al. used Desulfovibrio desulfuricans to remove scale and stains (black sulfate scale) from marble surfaces with excellent results;

Li Peihao from Zhejiang University of Technology and Qu Wenjun from Tongji University used Sporosarcina pasteurii as a test microorganism to prove that it can be used to repair concrete cracks, etc.

When microorganisms are used to repair stone cultural relics, they will form a layer of calcium carbonate mineralized film on the surface of the cultural relics. This "protective film" not only fits tightly to the surface of the cultural relics and has the same material as the cultural relics, but also has better performance in toughness and strength due to the compounding of several organic substances.

The reason is that most of the above-mentioned restoration cases utilized the ability of functional microorganisms to increase the concentrations of bicarbonate and carbonate, thereby enhancing the precipitation reaction.

So, what factors will affect the repair function of microorganisms?

First, temperature. All physiological activities of microorganisms are carried out within a certain temperature range, and there is an optimal temperature. Choosing the right season or creating a suitable environmental temperature can make these little guys work happily.

Second, pH value. pH value will have a significant impact on the ability of microorganisms to produce bicarbonate and carbonate. In actual remediation, workers often have to prepare buffer solutions to create a suitable acid-base environment for microorganisms.

Third, the types of microorganisms. There are many types of microorganisms that can be used for cultural relics restoration, each with its own characteristics and strengths. Therefore, it is necessary to analyze specific issues and select one or several microorganisms with the most suitable characteristics and functions for restoration.

Fourth, microbial density. The conduct of some physiological activities of microorganisms is closely related to their density. Only by ensuring that the density of bacteria meets the relevant "threshold" requirements can the restoration work proceed in an orderly manner.

While performing restoration work silently, microorganisms can restore the true appearance of cultural relics to the greatest extent possible. They do not require special equipment, are relatively labor-saving, are highly environmentally friendly, and have no secondary pollution problems. The cost is much lower than traditional methods, and therefore they have gained more and more attention and favor.

In addition, the microbial restoration process itself is "gentle", and the probability of accidental injury to implementers is low. This is consistent with the tone of harmonious progress between man and nature, man and culture, and man and society. Strengthening research and application of it can be said to be a natural move.

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