Imagine you’re Indiana Jones, and in one of your archaeological adventures, you find a mysterious object. You can learn about the composition of that object by using an elemental analysis method called X-ray fluorescence, or XRF. The advantage of XRF spectroscopy is that it can reveal the elemental composition in a non-invasive way. This way, we can continue to preserve the heritage objects.
How does X-ray fluorescence work?
To analyze an object, we bring the XRF instrument close to the area of the object we want to investigate, and we irradiate that area with X-rays. X-rays are high-energy electromagnetic waves.
After we send the beam of X-rays to that area, we then record with the help of a detector the radiation emitted as a response to the irradiation with X-rays. What we’re recording is the X-ray fluorescence. This recorded signal is then analyzed, and after the analysis, we can find out which chemical elements are present in the sample.
There are different types of XRF instruments—some are larger and are fixed in labs; others are smaller and portable. With the portable XRF instruments, we can record experiments even in more remote locations, like archaeological sites. The entire XRF experiment can be as fast as a few seconds or longer, lasting several minutes.
X-ray fluorescence spectroscopy
When we irradiate a material with X-rays, we can find out which elements are present in that material by analyzing the X-ray fluorescence energy.
At the atomic level, when we irradiate the sample with a beam of X-rays, in response to those X-rays, one electron from the inner shells is removed from the atom. With this electron out of the atom, now there’s a vacancy in one of the inner shells of the atoms. Then, an electron from an outer shell comes to the inner shell and takes the place of the electron that was kicked out by the primary X-ray. When the outer shell electron moves to the inner shell, an energy is released in the form of X-ray fluorescence. This energy is then recoded by the detector. And by analyzing this energy, we can find out which elements are present in the sample.
The X-ray fluorescence associated with each of these transitions has a precise energy value. This energy is given by the energy difference between the inner shell and the outer shell. In X-ray fluorescence spectroscopy, we obtain spectra where peaks are present at the energy values specific to the elements present in the sample. This reveals the elemental composition of the sample.
Applications of XRF in the elemental analysis of artwork
One of the advantages of using XRF in the elemental analysis of artwork is given by its non-invasive nature. This allows for the experiments to be recorded without damaging the investigated objects, which is of great benefit when analyzing precious objects of cultural heritage that need to be kept intact.
We can use XRF spectroscopy to analyze cultural heritage objects like paintings, sculptures, mosaics, coins, wall paintings, etc. The analysis can reveal details about the materials used in the construction of those objects.
Besides the elemental analysis and getting information on which elements are present in a sample, we can also record XRF mapping of artworks. So if we analyze a painting, we can obtain a full two-dimensional map of that painting showing the distribution of different elements in the painting. Scientists from the Metropolitan Museum of Art in New York recoded XRF maps of Van Gogh’s Irises and Roses and Johannes Vermeer’s Mistress and Maid, revealing which elements are present in which areas of the paintings.
By knowing which is the elemental composition of artwork, scientists can propose the best conservation and restoration methods suitable for those objects.