The Mona Lisa originally had eyebrows, according to a French art expert who has analysed Leonardo da Vinci's masterpiece with a special camera.

Pascal Cotte said da Vinci built the painting up in layers, the last being a special glaze whose optical properties increased the illusion of a three-dimensional face. Above the glaze Da Vinci painted details such as the eyebrows.

Cotte said: "That could explain why the eyebrows have disappeared – they have faded because of chemical reactions or they have been cleaned off."

He has uncovered a host of secrets about the Mona Lisa using a 240 megapixel camera. It can measure light so sensitively as to see through the top paint surface and uncover the layers below.

For example, infra-red imaging shows da Vinci moved the position of a finger on the left hand "to give a more relaxed position, consistent with the smile", Cotte said.

He said the Mona Lisa looked "totally different" 500 years ago, when it had a blue sky and the subject's skin had not yellowed.

The underlying layers of the face - painted using lead white and mercury vermillion - also show it was wider than the end result appears.

"The smile, the glance, the face were all wider," said Cotte.

But da Vinci did not change his mind half way through, he said. On top of the base layers the artist added a glazed shadowing layer to create a three dimensional effect.

"I do not say that he was successful, in reproducing a stereo-vision effect, but if you want to achieve that this is the best way to do it," said Cotte.

"But now it looks totally different to how he painted it. All the optical effects have disappeared."

He said that for da Vinci the Mona Lisa was "more than a painting, it was a challenge to reproduce real life".

法国一位艺术专家日前称，蒙娜丽莎原本有眉毛。这位专家在使用一种专业相机对莱昂纳多•达•芬奇的名作（《蒙娜丽莎的微笑》）进行分析后得出了该结论。

帕斯卡尔•柯特称，达芬奇在绘制这张画时使用了多层颜料，最表面的一层使用了一种特殊釉料，这种颜料的光学性能可增加人物面部的三维效果。在这层釉料上面，达芬奇绘制了眉毛等细节部位。

柯特说：“这可以解释为什么眉毛不见了，可能是由于化学反应褪色了，或是被擦掉了。”

柯特使用一款240兆像素的相机揭开了有关蒙娜丽莎的很多谜团。这款相机可以精确地测量亮度，能够透过表层“直视”下面的层次。

例如，从红外图像可以看出，达芬奇在作画时改动了蒙娜丽莎左手一根手指的位置。柯特说：“这个位置给人的感觉更放松，与她的微笑很相称。”

他称，五百年前的蒙娜丽莎和现在“完全不同”，当时画上背景的天空是蓝色的，人物的肤色也没有变黄。

此外，从使用铅白和银朱绘制的面部以下的层次可以看出，蒙娜丽莎的脸部原本比现在宽。

柯特说：“蒙娜丽莎的笑容、眼睛和脸部都比现在宽。”

他称，但达芬奇没有中途改变主意，之后，他在底层上添加了一层釉料阴影层来制造三维效果。“

柯特说：“我并不是说他在制造三维效果上做得很成功，但如果你想达到这种效果，这是最好的办法。“

“但现在，这幅画和最初达芬奇绘制它时已完全不同。所有的视觉效果都不见了。“

他表示，对于达芬奇来说，《蒙娜丽莎的微笑》“不仅是一幅画作，还是重塑现实生活的一个挑战