In a dark laboratory in Paris, Pascal Cotte sat back as his prized invention, a multispectral camera, performed its final scan of Leonardo Da Vinci’s Mona Lisa. With the imaging complete, he was ready, with the help of some self-coded computer programmes, to unearth each individual brush stroke behind one of the most iconic pieces of the art in the world.
Cotte is not your typical art historian. Achieving significant success in the field of optics developing the first Macintosh webcams, the bowtie-clad Frenchman has over 20 years experience in the technology industry. He now finds himself as Director of Research at Lumière Technology, the leading company for the digitisation of artwork. Cotte’s path to the art history world has been far from conventional. But his self-taught engineering skills combined with modern technologies may revolutionise the way we understand our cultural heritage.
His greatest success in the study of fine art to date is the development of a revolutionary camera, one that records 13 wavelengths of light. An impressive feat compared to the 3 used by an average camera. With each scan at a particular wavelength, the camera produces a spectrum based on the reflected light for each individual pixel of the image. This allows Cotte to uncover the exact materials – the pigments and oils – used to produce that region of the painting, helping conservators better preserve it for future generations.
Using his camera, Cotte can perform the layer amplification method (L.A.M.). This technique is based on the idea that different colours absorb specific wavelengths of light, meaning that pigments are opaque at one wavelength but transparent at another.
“[It] gives us the capability to peel the painting like an onion,” says Cotte, “removing the surface to see what’s happening inside and behind the different layers of paint.”
Cotte scans the painting in the visible light range, then the ultraviolet light range, a shorter wavelength, that allows detection of details on the surface determining areas that have been retouched or restored. Finally, infrared light, which has a longer wavelength than both UV and visible light, is able to penetrate the different layers of the paint, revealing the painting’s bottom layers, including preliminary sketches or hidden details.
With a prototype of his revolutionary camera complete, Cotte set out to uncover the secrets hidden within the famous Mona Lisa and create a complete digitisation of the portrait. His analysis provided scientific evidence to confirm Da Vinci’s unique painting technique called sfumato. Derived from the Latin word fumare, ‘to smoke’, the Master blended colours to make realistic shapes and shadows, without using harsh outlines. Martin Kemp, an Emeritus professor and world-renowned Da Vinci expert, describes the painting to be ‘like stained-glass’ as Da Vinci layered faintly tinted semi-transparent oils on top of one another, allowing light to pass through each layer, reflect off the white base and back through the oils, providing the portrait with a sense of realism that few painters have been able to replicate.
With the fame of his analysis and the respect of the art community behind him, Cotte’s services were called upon once again; this time to validate the authenticity of a chalk drawing of a young girl, La Bella Principessa. Once thought to be a sketch of 19th century German origin, sold as such in a 1988 auction, various experts, including Kemp, later attributed the work to Da Vinci. The validity of this portrait was highly controversial: the age of the materials were appropriate and the shapes and shadows, particularly around the very realistic eye, seemed to indicate Da Vinci’s hand. But the soft subject matter and unusual use of animal skins placed doubts in critics’ minds.
Working with Kemp, Cotte’s L.A.M. revealed the layering true to Da Vinci’s left-handed mastery. Additionally, the realism of the eye was brought to light, uncovering how a complete iris was drawn with the eyelid layered on top. This is truly an indication of Da Vinci’s technique in which he drew in details, not always obvious to the naked eye, to add to the realism of the portrait. Whilst the authenticity of the drawing is still in dispute, Cotte and Kemp’s work adds to the mounting evidence that Da Vinci is the artist behind this beautiful work.
Most recently, Cotte put L.A.M. to the test by analysing another Da Vinci masterpiece, The Lady with an Ermine. His scans revealed the sketches underneath, helping historians unravel the story behind this painting. Initially, the painting was a simple portrait of the mistress of the Duke of Milan, one of Da Vinci’s patrons with the nickname ‘The White Ermine’. However, a small ermine was added in, symbolising the young woman’s attachment to the artist’s patron. A third version of the portrait was layered on top, in which the ermine is larger and more muscular, emphasising the Duke’s power. According to Kemp, this new information “tells us a lot more about the way Leonardo’s mind worked when he was doing a painting. We know that he fiddled around a good deal at the beginning, but now we know that he kept fiddling around all the time and it helps explain why he had so much difficulty finishing paintings.”
Whilst using scientific methods to analyse paintings is still a relatively underdeveloped field, in his book Lumière on the Lady with an Ermine, Cotte predicts that “in the years to come, the L.A.M. technique is destined to become an indispensable complement to the analysis, study, certification and authentication of easel works.”