An international team of scientists used high-energy X-rays to analyze 12 fragments from ancient Egyptian papyri and found lead compounds in both red and black inks used. According to their recent paper, published in the Proceedings of the National Academy of Sciences, this is evidence that these compounds were added not for pigmentation but for their fast-drying properties, to prevent the ink from smearing as people wrote. Painters in 15th-century Europe used a similar technique when developing oil paints, but this study suggests ancient Egyptians discovered it 1,400 years earlier. So the practice may have been much more widespread than previously assumed.
“Our analyses of the inks on the papyri fragments from the unique Tebtunis Temple Library revealed previously unknown compositions of red and black inks, particularly iron-based and lead-based compounds,” said co-author Thomas Christiansen, an Egyptologist from the University of Copenhagen.
As I’ve written previously, synchrotron radiation is a thin beam of very high-intensity X-rays generated within a particle accelerator. Electrons are fired into a linear accelerator to boost their speeds and then injected into a storage ring. They zoom through the ring at near-light speed as a series of magnets bend and focus the electrons. In the process, they give off X-rays, which can then be focused down beamlines. This is useful for analyzing structure because in general, the shorter the wavelength used (and the higher the energy of the light), the finer the details one can image and/or analyze.
That’s what makes synchrotron radiation particularly useful for analyzing art and other priceless artifacts, among other applications. Back in 2008, European scientists used synchrotron radiation to reconstruct the hidden portrait of a peasant woman painted by Vincent van Gogh. The artist (known for re-using his canvases) had painted over it when he created 1887’s Patch of Grass. The synchrotron radiation excites the atoms on the canvas, which then emit X-rays of their own that can be picked up by a fluorescence detector. Each element in the painting has its own X-ray signature, so scientists can identify the distribution of each in the many layers of paint.
Last year, we reported on the work of a team of Dutch and French scientists who used high-energy X-rays to unlock Rembrandt’s secret recipe for his famous impasto technique, believed to be lost to history. Impasto (translated as “dough” or “mixture”) involves applying paint to the canvas in very thick layers. It’s usually done with oil paint because of the thick consistency and slow drying time, although it’s possible to add acrylic gels as a thickening agent to get a similar effect with acrylics. Rembrandt used it to represent folds in clothing or jewels, among other objects, in his paintings. The scientists discovered the presence of a mineral called plumbonacrite in the impasto layer—an uncommon element in paints from that period.
And earlier this year, we reported on