By Joanne Liou
The story behind a painting typically starts with identifying the artist and when the work was produced. And truth be told, there are some allegedly prized paintings that tell a story of criminal deception. Art forgery can be lucrative and go undetected, but analysis techniques, including radiocarbon dating using accelerator mass spectrometry (AMS), can reveal the fakes.
“Nuclear analytical techniques are extremely powerful in determining the composition, origin, authenticity and age of samples or objects, and hence have direct relevance to forensic science,” said a nuclear physicist at the IAEA, Aliz Simon. “In this context, nuclear techniques may be effective tools for a variety of purposes, such as the investigation of art forgery, detecting illicit trade, identifying counterfeited food and sub-standard medicines, and trace evidence analysis, for example, pieces of glass from a crime scene.”
Forensic science is the application of scientific methods or expertise to examine evidence to assist in criminal investigations. It comprises an array of disciplines, from DNA and fingerprint analyses to compositional and glass analyses. In the field of forensics, accelerators are used to analyse a material’s composition, structure, age and other properties. “X-rays, neutrons and ions offer advantages over conventional methods,” Simon said. “They can analyse one particle among millions and pinpoint origin with great accuracy, while leaving evidence intact.”
Nuclear analytical techniques are extremely powerful in determining the composition, origin, authenticity and age of samples or objects, and hence have direct relevance to forensic science.
All living things, including a painting’s canvas (made of natural fibres) or frame (made of wood), absorb carbon from the atmosphere, including carbon-14. Carbon-14 is an unstable isotope that decays at a known rate. When plants or animals die, they cease to absorb carbon, and the radioactive carbon already accumulated decays. The age of material can be determined by the amount of carbon-14 present, using AMS to measure the ratio of carbon isotopes. This technique, known as radiocarbon dating, is widely used to date fossils and, more recently, has been applied to date suspected art forgeries. “Radiocarbon dating of canvas provides the earliest date an artwork could have been produced because of the time between harvesting linen for canvas and the actual painting of the piece,” said Lucile Beck, manager of the Carbon-14 Measurement Laboratory at France’s University of Paris-Saclay.
The amount of carbon-14 in the atmosphere has fluctuated in recent history, specifically from the mid-1940s and 1950s because of nuclear weapons tests. Carbon-14 concentration in the atmosphere peaked around 1964 and has declined since. “We can easily identify materials containing modern weapons-derived radiocarbon because their level of carbon-14 concentrations is higher than pre-1950s levels,” Beck said.
During a 2019 investigation of potential forgeries by France’s Central Office for the Fight against Illegal Trafficking in Cultural Goods, Beck tested two paintings from a collection thought to have originated from the late 19th and early 20th centuries. Researchers collected samples of fibre from the canvases and reduced them to about one milligram of carbon that was then measured with AMS.
“With AMS radiocarbon dating, we were able to prove that the two paintings — one Impressionist and one Pointillist — were forgeries,” Beck concluded. “Based on the excess of carbon-14 detected in the fibres, the paintings had not been painted at the beginning of the 20th century by the alleged artists, who died in the 1940s. The content of the fibres revealed the canvases were manufactured in the mid-1950s or, more likely, after 2000.” The measured carbon-14 levels corresponded to levels before and after levels peaked in the 1960s.
Accelerating nuclear for forensic science
In 2017, the IAEA embarked on a four-year coordinated research project to enhance nuclear analytical techniques to meet the needs of forensic science. The project focused on three main areas: glass analysis, food authentication and cultural heritage, including the investigation of art forgery. Project participants were from Brazil, Croatia, Finland, France, Hungary, India, Israel, Italy, Jamaica, Portugal, Singapore, Slovenia, Switzerland and Viet Nam. Some results of the project, that range from the analysis of coffee to windshield glass samples, as well as the art forgery study in France, are already published in a special issue of the journal Forensic Science International.
Under the framework of the project, in 2019, the IAEA jointly hosted a workshop with the Abdus Salam International Centre for Theoretical Physics in Trieste, Italy. It highlighted how accelerator-based techniques can complement standard forensics methods in criminal investigations. Concurrently, the IAEA also launched an e-learning course on nuclear analytical techniques for forensic science.
Building upon the success of the project, the IAEA signed a Memorandum of Understanding with the United Nations Interregional Crime and Justice Research Institute (UNICRI) in 2021 to boost cooperation in preventing and countering criminal activities through nuclear science and technology.
As a next step, the IAEA plans to launch a follow-up coordinated research project focused on detecting the illicit trade of heritage objects and illicit mining of precious metals.