Ananova:

Scientists may have solved the mystery of the Mona Lisa's smile - they believe she had just given birth.

A team of Canadian French scientists reached the conclusion after studying Leonardo da Vinci's masterpiece with infra-red technology.

It allowed them to see beneath a layer of varnish and discover the model had a gauzy layer over her dress, reports the Globe and Mail.

The filmy robe, called a guarnello, was typically worn by pregnant women of the time, or mothers who had recently given birth.

Mona Lisa was Lisa Gherardini, the wife of Francesco del Giocondo, a Florentine cloth merchant.

Records suggest she wasn't pregnant when she posed for Leonardo, but that the painting was commissioned to celebrate the birth of her third child.

Bruno Mottin, curator in the research department of the Centre de Recherche et de Restauration des Musées de France, said the infant, a boy, was born before Leonardo began painting the Mona Lisa in the early 1500s.

The researchers carried out the most in-depth scientific study ever done on the painting, using a number of high-tech tools, including a three-dimensional laser scanner developed by Canada's National Research Council.

They carried out their work in a laboratory in the basement of the Louvre in Paris. They had to work at night, when the museum was closed.

They also found a veil visible on her head, Mona Lisa was wearing a dark bonnet that can't be seen under the layer of varnish applied long after Leonardo died.