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Is it light or humidity? Scientists identify the culprits of emerald green degradation in masterpieces

2025/11/192025/11/21

An international team of researchers have found what triggers degradation in one of the most popular pigments used by renowned 19th and 20th century painters. Using a multi-method approach, including advanced synchrotron radiation techniques, they’ve unveiled how light and humidity affect the masterpieces over time, and have proposed a strategy for its mitigation and monitoring. The results are out now in Science Advances.
During the 19th century, the Second Industrial Revolution sparked major advances in chemistry, giving rise to synthetic pigments that transformed art. Among them was emerald green, a vivid copper arsenite pigment admired for its brilliance and intensity.

Emerald green was used by well-known late 19th and early 20th century painters, such as Paul Cézanne, Claude Monet, Vincent van Gogh, Edvard Munch, and Robert Delaunay. Some of these painters, including Van Gogh, quickly realised that the paint would change over time, losing its original brilliant colour, cracking and triggering surface deformations. It was discovered later that it was also highly toxic.

Light and humidity

Researchers believe emerald green degrades because its chemical composition is highly unstable under light, humidity, and certain atmospheric gases. These conditions can cause the pigment to react and release arsenic compounds, alter its colour, or form dark copper oxides.
Now a research team led by the Institute of Chemical Sciences and Technologies “Giulio Natta” (SCITEC) of CNR and the Department of Chemistry, Biology and Biotechnology of the University of Perugia, in collaboration with the ESRF, the European Synchrotron, and the University of Antwerp, has investigated what triggers the degradation of emerald green. The study1 aims to improve strategies for preserving the masterpieces containing this pigment and to develop new methods to monitor their conservation state. “It was already known that emerald green decays over time, but we wanted to understand exactly the role of light and humidity in this degradation”, explains Letizia Monico, senior researcher at the SCITEC-CNR, corresponding and first author of the publication, together with Sara Carboni Marri, a former PhD student from the same research group.

Read more on the ESRF website

Image: Photograph of The Intrigue (1890, Royal Museum of Fine Arts Antwerp, KMSKA) by James Ensor

Credit: Royal Museum of Fine Arts Antwerp, KMSKA

Disorder begins at the surface of quantum materials

2025/10/172025/10/23

A new study reveals that the response of quantum materials to light is more complex than previously assumed. Using ultrafast X-ray pulses at the X-ray free electron laser SwissFEL, researchers found that the surface of a layered manganese oxide reacts differently than the bulk when its orbital order is disturbed. These results challenge the idea that light-induced changes happen uniformly and suggest that the path from order to disorder is shaped by local differences inside the material.

In certain materials, the electrons arrange themselves in a well-defined, ordered pattern. This internal order can influence everything from how the material conducts electricity to how it responds to magnetic fields. One example is the layered manganese oxide and quantum material La_0.5Sr_1.5MnO₄, in which electrons of manganese atoms arrange themselves into a regular pattern – known as orbital ordering – leading to distinctive electronic and magnetic behaviour.

Researchers are increasingly interested in how light can be used to understand and control the orbital state of these materials. With the right kind of light pulse, it may be possible to switch or reshape their properties at incredible speeds. Therefore, understanding how these materials switch is an important step to making devices.

In many devices, surfaces of and interfaces between materials are known to play a major role in the device properties. Yet until now, it has not been possible to measure how quantum materials change at the surface when switched at high speeds by light. Previous studies have only captured the average response over the whole crystal.

In this study, a team of scientists led by Aarhus University asked if the average response measured to date accurately captures the processes that occur at the surface, which will be relevant for any device. Remarkably, they found that they did not.

Read more on the PSI website

Image: Using ultrafast X-rays from SwissFEL, scientists have revealed unexpected light responses in quantum materials

Credit: © AdobeStock

Orbital angular momentum carried by an optical field can be imprinted onto a propagating electron wave

2020/10/232020/10/23

Photons have fixed spin and unbounded orbital angular momentum (OAM). While the former is manifested in the polarization of light, the latter corresponds to the spatial phase distribution of its wavefront. The distinctive way in which the photon spin dictates the electron motion upon light–matter interaction is the basis for numerous well-established spectroscopies. By contrast, imprinting OAM on a matter wave, specifically on a propagating electron, is generally considered very challenging and the anticipated effect undetectable.

We carried out an experiment at the LDM beam line at the FERMI free-electron laser, with the aim of inducing an OAM-dependent dichroic photoelectric effect on photo-electrons emitted by a sample of He atoms. The experiment involved a large international collaboration and surprisingly confirmed that the spatial distribution of an optical field with vortex phase profile can be imprinted coherently on a photoelectron wave packet that recedes from an atom. Our results explore new aspects of light–matter interaction and point to qualitatively novel analytical tools, which can be used to study, for example, the electronic structure of intrinsic chiral organic molecules. The results have been published in Nature Photonics.

Read more on the Elettra website

Image: A VUV free-electron laser (violet) is used to ionize a sample of He atoms, and an infrared beam (red) to imprint orbital angular momentum on photo-emitted electrons. Credit: J. Wätzel (Halle university)

New interaction between light and matter discovered at BESSY II

2020/04/232020/04/24

A German-Chinese team led by Gisela Schütz from the MPI for Intelligent Systems has discovered a new interaction between light and matter at BESSY II.

They succeeded in creating nanometer-fine magnetic vortices in a magnetic layer. These are so-called skyrmions, and candidates for future information technologies.
Skyrmions are 100 nanometre small three-dimensional structures that occur in magnetic materials. They resemble small coils: atomic elementary magnets – so-called spins – which are arranged in closed vortex structures. Skyrmions are topologically protected, i.e. their shape is unchangeable, and are therefore considered energy-efficient data storage devices.

Soft x-rays at BESSY II

In a series of experiments on the MAXYMUS beamline of BESSY II, the researchers have now shown that a bundled soft X-ray beam with a diameter of less than 50 nanometres can generate a magnetic vortex of 100 nanometres. In order to make the skyrmions visible, the researchers use the MAXYMUS scanning transmission X-ray microscope. This is a high-resolution X-ray microscope, weighing 1.8 tons, located at BESSY II.

Image: bundled soft X-ray beam with a diameter of less than 50 nanometers writes numerous magnetic vortices, which together form the term “MPI-IS”. Credit: Alejandro Posada, Felix Groß/MPI-IS

‘A day in the light’ Videos highlight how scientists use light in experiment

2019/05/162019/05/16

In recognition of the International Day of Light (@IDL2019) on May 16, the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) is highlighting how scientists use light in laboratory experiments. From nanolasers and X-ray beams to artificial photosynthesis and optical electronics, Berkeley Lab researchers tap into light’s many properties to drive a range of innovative R&D.
In the three videos displayed below, you will learn how light drives the science of Berkeley Lab’s Advanced Light Source (ALS), a synchrotron that produces many forms of light beams. These light beams are customized to perform a variety of experimental techniques for dozens of simultaneous experiments conducted by researchers from across the nation and around the world.

Image: Shambhavi Pratap, ALS Doctoral Fellow in Residence and a Ph.D. student at the Technical University of Munich, discusses how she studies thin-film solar energy materials using X-rays at the ALS.
Credit: Marilyn Chung/Berkeley Lab