New insights into some of the world's greatest masterpieces have been uncovered thanks to the wonders of science.
Researchers have for the first time offered a glimpse of the sketches underneath paintings by the Old Masters using a new x-ray machine.
The portable machine scans through the painting and reveals the undercoat beneath and has been used to look under Rembrandts, Caravaggios and Rubens, say scientists.
Not only does it offer a fascinating glimpse of the artists' techniques but could also be used to settle any arguments over the authenticity of some of the works.
The machine uses "macro X-ray fluorescence analysis" to examine the works, and does no harm to the priceless paintings.
An analysis of paintings from the workshops of Rembrandt and Caravaggio has shown that the underpainting was carried out in poor quality paint – a brown pigment probably recycled from leftovers as the artist scraped his palette clean.
Matthias Alfeld, at the University of Antwerp's said: "The underpainting was the first and most important step in creating a work of art.
"It was the sketch that guided the artist through the creative process. The Old Masters generally used to roughly indicate light, shade and contours.
"Observation of the underpainting would allow us to see the first execution of the artist's vision of the painting.
"It's a more detailed look over the shoulder of the artist at work. But the underpainting has virtually escaped all imaging efforts.
"So far, our methods to visualise the underpainting, except in localised cross sections, have been very limited."
But the technique could also settle disputes about who painted certain works, he said.
He said: "Using the new technique, we hope to disperse doubts about the authenticity of several paintings or to confirm that these paintings were not by the painter they have been attributed to.
"It is nice to show that the world of art can intersect with chemistry. Chemistry is such an all-encompassing science.
"Imagine, chemistry isn't just about molecules and reactions, but it also involves also the study of something as beautiful as great works of art."
The device was unveiled as scientists presented their work at the National meeting & Exposition of the American Chemical Society.