A new book about the best known painting on earth is liable to change your mind about it. The serene countenance of the half-length portrait of Lisa Gherardini, a.k.a. Mona Lisa, may not be one of contentment. Research by art historians Martin Kemp and Giuseppe Pallanti, reported in their book “Mona Lisa: The People and the Painting,” suggests that the half-smile may be a forced smile, pasted on for the sake of the portrait. If so, she had reasons.

Slave trade

The historians found that Lisa’s married life was surrounded by teenage female slaves that her husband, Francesco del Giaconda, bought and sold as his father did before him.

It’s likely that she started out as a slave, too, until Franchesco, twice her age, married her when she was 15 and pregnant. She bore six children in all and lost two. Wait, there’s more.

Francesco sent two of their daughters to a convent, which was the way of those without funds for dowries. Franchesco had wealth but opted for the nunnery anyway, which proved calamitous. At age 12, Camilla, the couple’s third child, entered the convent of San Domenico, the same cloister that Lisa’s two sisters, Sister Camilla and Sister Alessandra served. But they proved to be bad role models for her daughter.

Sex scandal

Historical records show that on April 20, 1512, four men snuck into the convent to join the waiting sisters for sex.

Caught in the act, the indictment against them read like a bad teen fiction. Other nuns were said to have looked on. When tried in court, the men were found guilty, and Lisa’s relatives were not. Their reputations, however, were surely sullied.

Sad end

The end of Lisa’s story isn’t any happier than her beginning as the teenage wife of a slave trader.

Suffering bad health, she ended up in a convent for the sick and died in anonymity on July 14, 1542. Franchesco never took possession of the portrait. Da Vinci kept it until he died. He had it with him when he was a guest of Francois I, king of France (which is how the painting ended up in the Louvre). Napoleon, apparently unaware of Lisa’s unhappy history, loved the portrait of Lisa so much that he hung it over his bed.

It’s no mystery

But 19th century critic Theophile Gautier seemed to understand that Lisas smile was forced long before Kemp and Pallanti suggested it. He wrote in 1857 about a melancholy he felt from seeing her portrait as it derided his belief in love with a “mocking smile.” Odd that no one had seen her facial expression as mocking before - even despite the constant scrutiny. As former Louvre director Henri Loyrette told the press that fully 80 percent of museum visitors come just to view Lisa’s portrait.