‘THE MULTISPECTRAL DIGITISATION OF TWO MONA LISAS’
An introduction by Pascal Cotte
“It was in 1998 that I designed the multispectral camera which permitted this form of scientific study. While working on this innovative project, I had always kept in mind that ‘La Joconde’ of the Louvre is clearly the most famous artwork in the world. More important even than its celebrity, it is a myth, an icon. From that time I had hoped that one day, from the exceptional knowledge I would acquire from the technology I was developing, I would be asked to analyse that masterwork of all masterworks and to place it under this new system of scientific investigation, and perhaps, who knows, to discover the secrets for its incredible reputation.
But all that is just speculation, for ‘La Joconde’ was already very famous before all this commotion. She was the object of numerous poems, drawings and caricatures, and continued to be the most copied painting in the world, of all time, anywhere. Proof of this is that very famous paintings with reputations equal to ‘La Joconde’, and recognised throughout intellectual circles and museums, have remained completely unknown to the public at large. For example, how many can recall that ‘The Concert’ by Vermeer, at the time considered as the most valuable painting in the world after ‘La Joconde’, was stolen as recently as 1990?
Therefore the ‘theft effect’ did not quite have the publicity result that one would expect. One must find another explanation.
In my opinion the secret is hidden in the meanderings of the various paint layers, in the fine superimposed glazes, in the pigment composition, and in the architectural arrangement of the graphic elements. Everything is competing to attract the observer’s attention and to bring him back to the common knowledge and ideas of human genres. It is far away from myth, from mystery, from the alchemy of the kabbalah, and of esotericism – rather it is the reality of the matter such that only science can analyse and understand.
In order to reap the rewards, there is a clear pre-requisite. To analyse ‘La Joconde’ it is first necessary to scan it photographically with the multispectral camera. Patience is a quality that is acquired over time, and it was more than 5 years later, on October 19, 2004, when the Louvre actually requested me to scientifically analyse ‘La Joconde’, the most viewed painting in the world with more than 8.5 million visitors every year.
I was finally able to begin the long scientific study which called for the assistance of the foremost specialists in fields dealing with the pigments, the varnish, mathematics, physics, and restoration. The multispectral camera delivered so much information – more than 3 billion pieces of data – that we first needed the means to separate them in order to sort and classify them. The further the research advanced, the longer the list of questions grew.
Certain answers were found in the comparison with other works by Leonardo da Vinci, where the provenance is beyond doubt. After extensive efforts we were able to photographically scan ‘The Lady with the Ermine’, at Kracow in Poland on September 3, 2007.
With the study of the ‘The Lady with the Ermine’ from Kracow, progress was significant, notably in the study of the glazes – those fine layers of paint which bring out the saturated colour. Their presence could be inasmuch confirmed on ‘La Joconde’ as it was absent on ‘The Lady with the Ermine’. Our knowledge of “The Art of Vinci” made a giant step.
The study of this ‘Mona Lisa’ painting was registered with exactly the same scientific steps as ‘La Joconde’, for the better understanding of the artwork of Leonardo da Vinci. The study of the pigment layers, the study of the characteristics of a painting on canvas, the study of the craquelure, etc. – there was a search for knowledge, a search for truth: to analyse and understand it.
Progress in the knowledge of these domains comes with the digitisation of all which can be found in these artworks: graphic studies, designs, portraits, parchments. The more we digitise, the more information we gather, and the more understanding we acquire.
The photographic process of this ‘Mona Lisa’, executed in September 2010 was a very important step in this work. First, there are the great emotions at the almost magical moment when one is given such a precious painting to place on the easel for analysis. Then, these emotions are further aroused by the first images which appear on the computer screen, and by the discovery of underlying features which had been previously totally invisible. They were unseen not only by the naked eyes of experts, but equally by the traditional tests undertaken by museum laboratories, such as the infrared reflectography and x-rays.
To see the preparatory drawing, to understand that a part of the painting was originally overpainted by the artist himself; all this is important, and often brings many answers to questions. That the landscape is so different in this version to that of the Louvre version is also a good example.
My work consists uniquely to provide information and objective elements. The information and details presented on this website are the best that can be produced today. They are the same revelations which have permitted some of the greatest experts of Leonardo da Vinci to recently identify ‘La Bella Principessa’ as an autographed work by Leonardo. That is a marvellous work on vellum representing a portrait of Bianca Sforza, the very young wife of Galeazzo Sanseverino, who died prematurely at the age of 14.
The important scientific elements and images, as revealed through the Lumiere Technology system, should form the basis of the intellectual effort, instrumental in regarding this exceptional version of ‘Mona Lisa’.”
Pascal Cotte, Paris
Analysis & Diagnostics 2010–2011
The painting has never changed: it has remained as Leonardo left it. Our ability to see and understand it, however, has changed radically over the last few decades, and more especially in the last few years. Whereas in medicine, newly developed Magnetic Resonance Imaging machines use powerful magnetic fields to align the magnetization of atoms in the body, and strong radio frequency fields to systematically alter the alignment of this magnetization in order to image nuclei of atoms inside the body, the technology for imaging artwork has also made a ‘quantum leap’ from traditional X-rays.
The Lumiere Technology company of Paris, France, has been developing special cameras for capturing digital images of archival material, including old-master paintings, since 1998. From the outset it was understood that part of the challenge of early multispectral imaging systems was not just the camera equipment, but also included the necessary lighting required to use it effectively. For example, to illuminate a large canvas of 12m2 using traditional methods would require 130,000 watts of power. Lumiere Technology overcame this challenge with a dedicated lighting apparatus that concentrates the light only where it is needed to capture the image, without compromising the integrity of the work. With this system, which requires only 2400 watts of power, the painting absorbs very little light energy, less, in fact, than 50 lux/hour, which is the generally accepted level for exhibition of drawings.
The vital importance of colour accuracy cannot be overstated. It affects literally everything in our lives. Colour is a visual phenomenon that results from rays of light being absorbed, reflected or refracted from the surface of an object. Because the amount of radiation emitted differs from one luminous source to another, and even from one geographical location to another, colours are perceived differently: an object does not yield the same colours in daylight, as when seen for example under tungsten or neon lighting conditions.
To understand and document some of these colour phenomena in terms of a painting or drawing, the spectral reflectance curves of the matrix of pigments that make up the pictorial surface need to be reconstructed. This is what occurs when the multispectral camera uses 13 different filters to gauge the reflected light on the various layers of the painting. The camera measures the ray diffused in its direction with a CCD array of 12,000 pixels in geometry where the total absence of parasitic specular reflections is guaranteed. A filter system in the camera cuts the luminous spectrum into 13 strips, staggered from the near UV (380 nanometers) to the near IR (1050 nanometers). The 13 measurements are then taken at the maximum resolution of 240 million pixels, and are supplemented with an incident light measurement. The total acquisition can be more than 6 billion bytes (octets).
Knowing that a painter used a glaze is one thing: proving it scientifically is another. Lumiere Technology was able to demonstrate this in 2008 on the superficial layer of the face of the Louvre ‘Mona Lisa’, using the multi-spectral technique. The results prove that multiplying the measurements can provide invaluable information on how the pigments are applied. It may therefore be possible ultimately to identify the painter’s technique, proofs and ‘signatures’ that can help with attribution and expert appraisal. Furthermore, the Lumiere Technology digital equipment can restore to sight the original colours with an unequalled colorimetric precision; to bring out from the infrareds the underlying sketches or preparatory outlines; and from the false colour infrareds to reveal the painter’s palette.
The quality and potential of this latest technology has been quickly recognized for its excellence, and its use has already been availed of by prestigious galleries and museums world wide, as well as by the owners of important collections. The process, under the supervision of engineer Pascal Cotte, the Scientific Director of Lumiere Technology, has already also been used to examine Leonardo’s ‘The Lady with the Ermine’ (portrait of Cecilia Gallerani) in 2006; ‘La Bella Principessa’ (profile of Bianca Sforza) in 2008; and most significantly, two versions of the ‘Mona Lisa’ – the Louvre’s in 2004, and the earlier painting as recently as September 2010.
There were 3 major factors in the determination to have the ‘Earlier Mona Lisa’ scanned with this equipment:
- Firstly, the constant pursuit of knowledge by The Mona Lisa Foundation, which influenced the owners to invest in more research about the painting. It was felt that this new information would reinforce the integrity of everything previously documented about the work.
- Secondly, Mr. Cotte has great experience with Leonardo’s paintings, and must be considered one of the world’s leading authorities when it comes to scientific knowledge on Leonardo: therefore the examination provided invaluable points of reference for both parties.
- Thirdly, having already scanned the Louvre ‘Mona Lisa’, this test would enable Mr. Cotte to make a unique comparison with the only other painting in existence that pertains to the same subject; that has similar Leonardesque ‘signatures’ throughout; and that has long been verified as a work by Leonardo da Vinci.
A summary of the results of the Lumiere Technology analysis of the ‘Earlier Version’, and other relevant comments, are as follows:
- All pigments used were common on Leonardo’s palette, and were available at the beginning of the 16th Century in Florence.
- The painting has some clear underdrawings, by the columns and elsewhere.
- Mr. Cotte remarks numerous times that “…the hands are extraordinarily beautiful”.