The secret of how Leonardo da Vinci produced the optical effects of the Mona Lisa's smile can be revealed for the first time.

(Kazan, August 23, Tatar-Inform). The secret of how Leonardo da Vinci produced the optical effects that created the Mona Lisa's enigmatic smile can be revealed for the first time.

Scientists have discovered how the artist managed to achieve his trademark smoky effect, known as sfumato, on the painting; by applying up to 40 layers of extremely thin glaze thought to have been smeared on with his fingers.

Using X-rays to study the painting, the researchers were able to see how the layers of glaze and paint had been built up to varying levels on different areas of the face. With the drying times for the glaze taking months, such effects would have taken years to achieve.

The scientists also suspect that he used his fingers to apply the glaze to his paintings as there are no brush marks or contours visible on the paintings.

Leonardo is known to have employed the sfumato effect to seamlessly blend shading together and to blur outlines. But the exact techniques used to achieve this have long fascinated and intrigued art experts.

The new discoveries have been made by scientists at Laboratoire du Centre de Recherche et de Restauration des Musees de France and the European Synchrotron Radiation Facility, The Daily Telegraph reports.

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