Atoms in preserving the past

J. Devaprakash, Tarapur Atomic Power Station in Maharashtra

2023-04-12 11:14:41



Italian polymath Leonardo da Vinci needs no introduction. He was a man apart. Perhaps, he was the most versatile human being ever to have lived. Da Vinci was a virtuoso in paintings, science, engineering, writing, sculpture, architecture and in numerous other fields.

Two of his paintings Last Supper (created during 1503-19) and Mona Lisa (created during 1595-98) still top the list of much-viewed paintings in the world. While the former is worth 450 million US dollars, the latter is valued as 1 billion US dollars. To add to his credit, he had also authored several more art works that became all-time wonders among art lovers across the globe.

But how such several centuries-old paintings and cultural heritage are conserved as they get withered with time or corroded or degraded owing to biological attack? Much known for electricity generation, nuclear technology helps keep the arts artefacts and manuscripts intact for ages. “Preserving cultural heritage using nuclear technology helps us to understand and respect the history, knowledge and experience of the countries as well as contributes to the socioeconomic benefits,” according to the International Atomic Energy Agency.

Conventionally, two methods, chemical and physical, were widely used to preserve the arts and artefacts. Nonetheless, owing to the drawbacks in these methods – while chemical method has a strong possibility of leaving unwanted substances on the object, the physical method can scathe the object itself – art conservators have turned to nuclear radiation technology to safeguard the objects of cultural importance from degradation.

With the invention of X-ray by the German engineer Rontgen in 1895 and the discovery of gamma ray by the French chemist Paul Villard in 1900, the way of preserving cultural heritage assets got changed. This ionizing radiation with high penetration power became prevalent in disinfecting the age-old artefacts in a non-destructive manner. Unlike the conventional methods, this radiation technology neither involves any chemical nor leaves any substance on the object. Since things happen in atomic level (smaller than even nano level) there is literally no chance of physical harm to the cultural asset.

According to the National Research Centre of Egyptian Atomic Energy Authority, “using nuclear radiation technique bio-deteriorating agents such as bacteria, fungi and insect eggs can be removed quickly from the artefacts without damaging it.” When the Egytian tombs were infested by large colonies of parasites, it was the radiation technique that came to rescue the wall paintings on the tombs. Similarly, the mummy of Ramses II, an Egyptian pharaoh and a great warrior, was disinfected using the same technique. Restoration of Ramses II was very crucial for historians as he was the third ruler of nineteenth dynasty who envisioned a great nation and himself as a ruler of rulers. Two of his creations – the rock-cut Abu Simbel temple, one of the most beautiful temples of Egypt, and the temple of Karnak which was believed to be the spot where creation began – made him admirable both during and after his lifetime.

Almost a decade ago, at Siberia, a tiara made up of 50,000 year-old woolly mammoth tusk was unearthed in a completely infected condition. Art restorers have employed the ionizing radiation technique through which energy was transferred to the microorganisms that lived inside and on the object. Resultantly, the germs on the tiara were neutralised without harming the object and the artefact was restored in a best possible manner.

Finding the age

When an archeologist excavates a new artefact, in the first place he tries to figure out the time period when the artefact was made or used. In art world, this process is known as dating. Determining the age of the artefact is crucial as it helps unfold numerous other associated characteristics about the object. According to experts, the most common method to precisely date or identify the age of an object is radiocarbon dating. This process involves measuring of carbon-14 atom, a radioactive isotope of carbon, on the artefact. In 1946, American physicist Willard F. Libby developed this method of dating which earned him recognition as a Nobel Laureate.

Carbon is a chemical element on earth – stored in rocks and sediments, and found in atmosphere, ocean and even in living organisms. Carbon-14 is an isotope, rather another version of carbon atom, which is a component of atmospheric carbon dioxide. When the nitrogen atoms in the atmosphere collide with cosmic rays, carbon-14 is formed persistently, and thus it is ubiquitous. In his paper “Art, archeology and the atom”, published in The UNESCO Courier in 1981, Bernard Keisch wrote “since the flux of neutrons has been nearly constant for the last several thousand years, the rate at which carbon-14 is produced by this means has been just as constant.”

All the living things on the earth absorb carbon-14. But when animals and plants die, they stop taking it. But their body will contain carbon-14 that they have absorbed when they were alive. This absorbed carbon-14 decays gradually at a constant rate with time. The half-life, the time taken for its radioactive atoms to decay into half, of carbon-14 is about 5,500 years. Means, after about 5,500 years the half of the carbon-14 in the artefact will disappear. By comparing the carbon-14 in the object (the residual radioactivity) with the living organism ratio, it is possible to determine the age of ancient objects such as paintings, artefacts, mummies, fossils and etc. And through this simple but most reliable method of dating, age of an object as old as 50,000 years can be determined.


Finding the fakes

Countless fakes are swaying in the art world. Distinguishing the authentic work from duplicates is tricky as well as arduous. In 2021, a copy of Leonardo da Vinci’s Mona Lisa was sold for 3.4 million US dollars at an auction. Raymond Hekking, the French art collector who bought the painting, tried hard to prove that his possession was the real work of Leonardo. But it was turned out to be the other way round: Global art experts judged that the art bought by Hekking was a canvas one whereas da Vinci’s original work was on a wooden panel.

X-rays is one of the technologies that are widely in use to examine the originality of the art. Usually, the original paintings would have alterations or over-painting as the artists make mid-course changes for the painting to evolve. But in copy, the artist knows from beginning how the painting should look like and as a result it is unlikely that alterations or over-painting is seen. X-rays help to reveal this fact as in denser areas of the painting show up lighter. Another way to expose the fake painting is to unraveling the hidden painting through X-ray as the forger generally employs re-used canvas or support belonging to the time period of the original painting.

For the past more than five decades nuclear science has been playing a significant role in the art field. Museums across the globe are employing nuclear techniques to preserve the most valuable and culturally important arts and artefacts, to date the discoveries and to identify the fakes. In fact, in 2021, both nuclear and art fraternities came together to celebrate the 50 years of atoms service in preserving the priceless past. As the Head of ARC-Nucleart, a France based art preservation agency that operates a unique irradiator in the world which is devoted to heritage conservation, put it, “before the use of nuclear techniques we lost or partially lost several objects of cultural value… but over the last half a century this problem has been mitigated through the use of radiation for conserving archeological, historical and cultural objects.”