That's how the Mona Lisa is preserved

You certainly know the Mona Lisa, also called 'La Joconde' in French, one of the most famous works of art in the world. And you probably also know that the painting is in the world-famous Louvre in Paris. But what you may not know is that Vaisala is helping to preserve the Mona Lisa by measuring the stability of humidity and temperature conditions inside the glass case.

This 77 x 53 cm portrait of a woman named Mona Lisa was created by Leonardo da Vinci. The portrait is believed to have been painted in the early 16th century. Every year, millions of people from all over the world visit the Louvre art museum in Paris to admire the enigmatic smile of the Mona Lisa.

A state-of-the-art air handling system allows air to circulate through the display case, surrounding walls and timber frame to maintain relative humidity and temperature at desired levels. As "La Joconde" was painted with oil on a poplar panel, it is important for its conservation to keep the humidity at an appropriate level. Changes in moisture can cause poplar wood to contract and expand. After 500 years, the wooden material shows signs of warping.

And this is where Vaisala comes in. Not visible to the public, two Vaisala HMT333 humidity and temperature transmitters were installed in the display case behind the painting. One gauge is near Mona Lisa's right hand and the other near her right eye. The relative humidity is kept constant at 50% RH and the temperature at 21 °C. In addition, two layers of silica gel in the wooden frame serve to compensate for fluctuations in relative humidity. The showcase is opened once a year. Then all the installed equipment is carefully inspected to ensure the Mona Lisa is treated properly. The display case is then closed again and the Mona Lisa is cared for in a state-of-the-art manner for another year.