Never-before-seen chemical effect spotted on Van Gogh masterpiece

Analytical chemistry researchers have uncovered a never-before-seen chemical effect in Vincent Van Gogh's Flowers In A Blue Vase, which is impacting some colours on the famed painting.

High-intensity x-ray studies were used by researchers from the University of Antwerp to uncover the chemical compounds called oxalates, which are responsible for the damage. It's not the first time the bright yellows have been examined with x- rays, previous research reported that a pigment Van Gogh favoured called chrome yellow degraded when other, chromium-containing pigments were present.

Building on these results, researchers took a tiny sample of the work to some of Europe's largest sources of X-rays: the ESRF in France and
Desy in Germany. Both of these research facilities use vast particle accelerators to speed up electrons, which spray out X-rays as they pass around the accelerators.

The intention of the study was to determine both what was in the samples in terms of atoms and molecules, as well at the precise structure in the interface layer between the original paint and the varnish. This is where the researchers made the shocking discovery, finding that cadmium oxalate was the cause of the grey-orange pallor.

Dr Janssens told BBC News: "The contact layer between the varnish and the paint, where the cadmium oxalate is found, is micrometer thin.

"If we had not used methods that allow us to interrogate this very thin layer, we would never have noticed that there were oxalates there."

These are properties most commonly found in older works and associated with different pigments. This was the first time researchers had found that cadmium forms oxalates within the varnish - a protective measure that was added much later.

"Van Gogh didn't like to varnish his paintings - he liked them, let's say, rough," Dr Janssens said.

"It was only after he died that these paintings found their way into the art market and into private and public collections and individual conservators would say 'we're going to varnish it because we do that with all our paintings'."