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Dhaka Tuesday,  Jan 23, 2018

Atomic methods: How to get insight into archeology and identify art forgery

Andrey Akatov / Yuriy Koryakovskiy

Radioactive atoms and radiation have been around well ahead of the origin of life on our planet. All substances contain radioactive isotopes that appeared, presumably, at the time of the formation of the Earth. Studying the distribution of natural radioactive nuclides in the environment makes it possible to understand some certain processes that are hardly approachable otherwise.

Atom 100 Million BC, or what the radioisotope dating method is all about

Archeology has become one of the most important fields of application for natural radioactivity. We are referring to the invention of the radioisotope dating method, or radiocarbon analysis. It is based on the fact that carbon contained in the atmosphere consists of three isotopes: stable carbon-12 and carbon-13, and radioactive carbon-14.

Carbon-14 is continuously produced in the atmosphere due to cosmic irradiation, and at the same time it undergoes nuclear decay. The result is that the share of carbon-14 nuclei keeps staying the same. Plants consume atmospheric carbon via photosynthesis, animals eat plants and each other. Therefore, while they are alive, the share of carbon-14 in living beings equals that in the atmosphere. But when an organism dies, its carbon exchange with the atmosphere ceases. Carbon-14 gradually decays, its quantity diminishes as there is no other source of it (insentient substances do not absorb СО2 from the air). Knowing the proportion of carbon-14 in the atmosphere, which is virtually constant, and having measured the proportion in the biological material in question, one can figure the organism’s time of death.

What use can be made of it? In 1950, near Tollund village (Denmark) peat miners discovered a well-preserved male corpse at a depth of two and a half meters. At first, it was assumed to be the victim of a recent untraceable murder. But when the scientists examined the body, it turned out that the man had died around the 4th century BC!

Radiocarbon analysis was developed in 1946 and has been successfully applied ever since. Another use of this method is revealing art forgery. Let us say you are offered a very expensive 18th century painting for purchase. Being in a doubt, you send it for dating expertise based on the content of carbon-14.

The laboratory cuts off a piece of the canvas, burns it and identifies the share of the isotope in question. After that, they do a calculation to estimate the time of the canvas’ manufacture (more precisely, the time of death of the plant whose fiber was used to make the canvas). If it is the 20th century, then the painting is definitely fake. Similar dating methods are used for wooden objects.

Atom longa, vita brevis, or how to see Van Gogh’s women with an X-ray

Fluoroscopic methods are widely used by scientists to research a material’s composition and structure. By exposing your sample to X-rays, you can identify what it consists of. Most importantly, this is a non-destructive method, which does no damage to the object.

For example, you need to know which metal is a piece of jewelry made of. What if the seller switched cheap copper for your gold? A regular chemical test would require dissolving the piece, which is unacceptable. Instead, you can examine it with an X-ray and get a precise answer in just a few minutes. In this case, your jewelry will stay intact and you can continue wearing it.

The two methods described above are of invaluable aid to fine art experts. The two important problems that they face on the job are of estimating the age of an object and revealing forgery. For example, the chemical composition of colored and white paints used in a painting can say much about the time of its creation.

Until the 19th century, white paint was mostly manufactured with lead, later with zinc, and in the 20th century it contained titanium. These elements are easily traceable by fluoroscopic analysis. Modern microprobe analyzers make it possible to identify paint composition even in a particular spot of the painting. This makes it possible to create an element distribution map of the canvas surface, also showing internal layers of paint that are otherwise hidden from the viewer’s eye.

Thus it has become possible to see a woman’s portrait hidden under the layers of paint in the Patch of Grass by Van Gogh. Apparently he often reused his finished paintings as canvases for new ones.

In a similar way, scientists managed to read the notes of one of the arias of the famous Medea by Luigi Cherubini, which had been marked out by the author. The researchers knew that late 19th century ink had a high content of iron, and the printing color used for printing staff contained significant amounts of zinc. Scanning one line after another with a microprobe analyzer set to detect iron and zinc, the researches deciphered the hidden notes.

Tomograph mon amour, or how to unwrap a mummy with the atom

Modern X-ray tomographic scanners are fantastic devices that have come into real life from science fiction. Not only doctors use computer tomography. Archeologists studying the ancient world are well aware of its potential as well. Let’s speak about Egyptian mummies, for example. These silent witnesses of the Ancient Egypt’s lifestyle can tell scientists a lot. But how to make them share their knowledge?

Mummies often contain funeral accessories and other important artefacts that would be great to examine in details. A mummy could, of course, be unwrapped, but that sounds somehow like a lack of respect. Besides, a museum exhibit would be irreversibly destroyed with no way of restoring it. But modern tomographic scanners make it possible to see all the details, leaving the covers untouched.

A lot of similar research has already been conducted. Thus, scientists have managed to visually examine the amulets of one mummy and read some of the inscriptions on them. They even identified possible cause of death of the person, having noticed cholesterol plaques in their veins. Another mummy’s analysis showed very bad teeth and serious mistakes of the embalmer (we are wondering if he had been paid!). And all these facts were revealed without damaging the millennia-old bodies, practically without touching them.

In 1754, an archeological excavation in Herculaneum, the city that died along with Pompeii, discovered a few papyrus rolls. Precisely, a few burnt papyrus rolls containing texts written with soot-based ink, aged almost two thousand years. Trying to unroll them was useless: they would have decomposed. But how to read the text? Recently scientists decided to use computer tomography, which enabled them to model a “virtual” papyrus roll and unroll it on the computer screen.

(Andrey Akatov and Yuriy Koryakovskiy are senior lecturers at St. Petersburg State Institute of Technology in Russia)


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