Spectroscopy techniques can be used to identify the chemical make-up of the pigments used by an artist – providing information about when and even where it was painted.
A team of scientists lead by Professor Daniela Comelli from Polytechnic University of Milan have used a technique called Raman Spectroscopy at the Central Laser Facility (CLF) to study the chemical make-up of pigments used in a series of Russian paintings from the early 20th century. The results, which were able to identify the types of pigments used and when the paintings were created, could be also used in future art restoration and conservation projects.
Several spectroscopic techniques, which study what happens when matter and radiation interact, have been used for decades to reveal the chemical composition of objects. Spectroscopy can be used to unveil the chemical make-up of things ranging from compounds in a laboratory to that of stars thousands of light years away. More recently scientists have been turning their spectrometers to the world of art, revealing the spectrum emitted by the paints, pigments, binders and other material the artist used to create the painting.
Optical spectroscopy is a particularly useful tool in the conservation and restoration of old or delicate artwork where it can be used to measure the colour of a sample and then match the findings to a database to identify the materials used – all without ever having to damage, or even touch the painting. As well as identifying the contents of the artist’s palette, the technique can reveal the time period and even the region in which it was created. It can also be used to help identify what might be causing an artwork to degrade or break down, which makes it easier to repair and preserve the painting. You could say that it bridges the gap between art and science.
Raman spectroscopy offers a simple and non-destructive way to analyse paints, pigments and resins. The technique works by exposing the object under investigation to the radiation in the form of light photons from a laser. The photons interact with molecules in the sample and scatter, losing energy as they do so. By detecting the scattered photon and measuring the energy the photon has lost, scientists can identify the chemical element from which it scattered.
The researchers have used the technique to investigate the chemical properties of pigments used in a series of Russian avant-garde paintings (the name given to experimental, or non-traditional artwork). The team from the physics department of Polytechnic University of Milan and the Institute for Photonics and Nanotechnologies looked at samples from oil paintings by Mikhail Larionov (1881-1964) and Natalia Goncharova (1881-1962), who were leaders in the Russian avant-garde movement in early 20th century. Raman Spectroscopy was combined with a technique called photoluminescence.
Over years, the chemicals, or compounds, used in the pigments that make up the artist’s palette have evolved with the technologies available at the time. For example, the ancient Egyptians used a combination of limestone, sand and copper that they heated to create a blue glass that was then ground down; while in Afghanistan artists used the semi-precious stone lapis lazuli. Fast forward to 18th century Germany and you’d find blue being made by roasting cobalt and tin oxides. So the chemicals and processes used to make pigments can inform when and even where they were made. This information can help identify forgeries too – no matter how convincing the artwork might be, if it uses pigments not available at the time, it’s a safe bet that the painting isn’t authentic.
In one of the paintings from the artist Goncharova, the scientists identified three distinct layers of colour in the sample – a layer with two shades of yellow mixed with a greenish colour sat beneath a white layer mixed with brown and a smaller blue layer mixed with white. In the white layer, for example, they found the spectrographic signatures of two white components – titanium white and zinc oxide (zinc white was in use from the mid-19th century). From this, they have been able to conclude that the painting was likely to have been painted prior to 1920 (during the artist’s ‘Paris period’) because, after this date, they would expect to find a white pigment based on titanium (titanium white) when a French firm started intense production.
Having demonstrated the effectiveness of their technique, the team propose that the method could be used to study samples taken from ancient sculpture and wall paintings and help to inform future methods of restoration and conservation.
Last updated: 26 September 2019