Unmasking the Mona Lisa: Expert claims to have discovered da Vinci's technique

For five centuries, art historians have puzzled over how the Mona Lisa was painted. Now a French artist says he has discovered the method behind the genius. By John Lichfield

A French artist and art historian claims to have cracked the real Da Vinci code - the mystery of how Leonardo painted the Mona Lisa.

Jacques Franck - a controversial figure but an acknowledged authority on Leonardo da Vinci - believes he has solved a conundrum which has defeated art experts for almost 500 years. In The Da Vinci Code, the best-selling thriller by Dan Brown, the Mona Lisa is said to contain clues to a 2,000-year-old conspiracy to deny the real character of Jesus Christ.

In real life, M. Franck believes that the painting does contain a code of a different kind - the five-centuries old secrets of a genius whose work has never been surpassed. "From the technical viewpoint, the Mona Lisa has always defeated all understanding," M. Franck said. "How did Leonardo da Vinci do it? I believe that I have the answer."

The Mona Lisa was painted in the early 16th century on a panel of poplar wood. Much of the brushwork on her face and hands is so small that it cannot be picked out by X-ray or microscope: a near-magical method of painting that Leonardo called "sfumato" or "smoky finish". The colour and shading melt into one another without visible joins or boundaries. After years of study and personal experimentation, M. Franck believes he has approximated Leonardo's method, if not the final result. His claims have been rubbished in the past by other Leonardo scholars. They say that he can produce no technical evidence to substantiate his claims.

From this month, however, M. Franck's approach has been given the official backing - or at least an official showing - by one of the leading art museums in the world, the Uffizi Gallery in Florence. As part of an exhibition on Leonardo which lasts until next January, the Uffizi is displaying eight of M. Franck's works. They include six tableaux which demonstrate his theories on the different stages in the creation of one of the Mona Lisa's eyes. The Uffizi is also displaying his re-creations of two other Da Vinci paintings, including Portrait of Saint Anne from the National Gallery in London.

M. Franck, consultant scholar at the Armand Hammer Centre for Leonardo Studies in Los Angeles, believes that the Mona Lisa was painted in hundreds of sessions with a technique of ultra-fine hatching - or criss-crossing of brush strokes - some as tiny as one-fortieth of a millimetre long. He says layers of extremely diluted oil paint were piled up on one another over many years - using perhaps 30 "coats" of paint in all. For his finer work, Leonardo probably painted with a brush in one hand and a magnifying glass in the other. It was through this method, M. Franck says, that Da Vinci achieved the sublime effects which astonished and irritated fellow Italian painters at the time and have puzzled art historians ever since.

Light and shadow on the enigmatic face and folded hands of the Mona Lisa move from one colour to another, and from one gradation of light to another, without perceptible "boundaries". Even the darkest shadows on her flesh seem to glow with an inner light. Other Renaissance painters went on to achieve something close to this effect. But Leonardo was the first painter to abolish the impression of a painting as a "coloured-in" drawing. His achievements in this area have been approached but never surpassed.

Leonardo da Vinci wrote in one of his treatises on painting: "Although the definition of boundaries is lost when a painting is viewed from distance, the painter himself should not neglect to achieve a smoky finish and not [leave] boundaries and profiles which are sharp and harsh."

To explore Leonardo's methods, M. Franck has resorted to a form of artistic retro-engineering. After studying the painter's descriptions of his own work, and the painting itself, he set out to try to recreate sfumato. He says that it took him 3,000 hours to complete his copy of Saint Anne. The world's most famous painting may have taken Leonardo far longer than that.

Leonardo da Vinci began the Mona Lisa in 1503. He was still working on her when he emigrated to France in 1516. He is believed to have finished the painting just before his death in 1519. In other words, he took almost two decades to paint the portrait of Lisa del Giocondo, née Gherardini, a Florentine gentlewoman. The Mona Lisa (an English-language spelling mistake for Monna, or "My Lady", Lisa) is believed to be the only painting which Leonardo finished to his own satisfaction.

The sfumato method is not the only revolutionary aspect of the Mona Lisa. Leonardo was an early pioneer of the use of slow-drying oil paints. The Lady Lisa's pose - staring back defiantly and superciliously at the viewer, not averting her eyes - was unorthodox in the early 1500s and much copied. By having her look slightly away from centre and displaying her hands, Leonardo achieved an impression of movement and three-dimensional presence, which had rarely been attempted before.

In his Mona Lisa: the history of the world's most famous painting, published in 2001, the British historian Donald Sassoon traces the origins of the Mona Lisa mystique through five centuries. He concludes that the revolutionary techniques and the beauty of the painting alone cannot explain the Mona Lisa's fame. Her status as "the one painting everyone knows" is, he says, the "product of a long history of political and geographical accident, fantasies conjured up, connections made, images manufactured, and luck..."

In the mid-19th century, she was re-discovered by British and French writers in the Louvre in Paris and turned into an object of mystery and almost of lust. In 1869, in a passage later made into poetry by W B Yeats, the British critic Walter Pater promoted the Mona Lisa as a kind of elemental mother-temptress and madonna-femme fatale, uniting the age-old male fantasies and myths of womanhood.

In recent years, the image of the Mona Lisa has been hijacked to advertise everything from condoms to horsehair corsets, from oranges to inter-uterine devices, to The Da Vinci Code.

Through all the vicissitudes of the Mona Lisa's fame, Leonardo's technique has continued to fascinate and baffle art historians. M. Franck - without claiming to know all the answers and certainly without claiming to have emulated Leonardo's talent - believes that he has finally cracked the real Da Vinci code.

He believes that Leonardo began with a sketch. But what happened after that? "The fundamental problem of sfumato is to know how shadow and light were joined invisibly," he says. "I believe that Leonardo used a technique which I call micro-division. Over a base coat - called the imprimatura - in pale yellow, Leonardo da Vinci started by creating contrasts by using very diluted, reddish tones. Then he went over the shadows very finely with a system of hatching." Leonardo then, M. Franck believes, "veiled" each stage of the hatching with another coat of imprimatura to "mask or abolish the sharp outlines of her form".

All of this was achieved by using brushstrokes which became finer and finer, using diluted paint. Each stage or layer was painstakingly covered with another "veil" of pale yellow.

The brushstrokes never exceeded one or two millimetres in length. "When it came to Mona Lisa's face," he said, "I believe that Leonardo must have applied 30 layers. He must have worked with a magnifying glass, getting down to brushstrokes no longer than one-thirtieth or one-fortieth of a millimetre." In other words, the smallest brush-strokes are smaller by far than the head of a pin.

Using hatching techniques was not new, M. Franck says. They had been used since Roman times to give an impression of relief. The use of oils allowed painters to give an even deeper sense of contours. He says: "What Leonardo did was to bring both the methods together in his determination to give an extraordinary sense of depth."

Leonardo may have had to wait for several days for each small area of hatching to dry before adding the next layer (magnifying glass in hand). He was therefore also proof of the adage that "genius is an infinite capacity to take pains".

M. Franck's approach has been rejected by some academic specialists. They say that his work is based on guesswork and surmise rather than scholarly research. Precisely because Leonardo's brush work is "invisible", they say, it is impossible to say for sure how he did it.

M. Franck says that the effects achieved by his own tableaux and paintings prove that he is, at the very least, moving in the right direction. Little by little the academic barriers to M. Franck's theories are breaking down.

The French national art laboratory C2RMF has also been using modern techniques to explore and analyse Leonardo's methods in painting the Mona Lisa. The results will be published this June in a book called Au coeur de La Joconde, Léonard de Vinci Décodé. La Joconde is the name given to the Mona Lisa in France. The book isexpected to reveal that Leonardo began with a sketch, as M. Franck suggests. The outlines of the sketch have been discovered under the painting by experts at the Louvre.

Jean-Pierre Mohen, in charge of the project at C2RMF, said M. Franck's other theories are matched by some of his team's own discoveries, but from a different perspective.

"He has moved knowledge forward, not in an analytical way, but experimentally," he said. "The Mona Lisa was a work which was accomplished slowly, meticulously, with enormous power of thought and experience of life. And all that to re-create a smile which must originally have lasted for only a quarter of a second."