Pascal Cotte is an engineer, inventor, and photographer. Now he can add discoverer to that list. His groundbreaking research reveals secrets about the world’s most famous portrait. The art world gawked—and then began speculating about unknown versions of the lady with the mysterious smile.

In 2004, Cotte received permission from the Louvre Museum in Paris to scan Leonardo da Vinci’s celebrated Mona Lisa. He captured more than 1,650 images and spent the next 16 years analyzing them.

Cotte’s painstaking study revealed that da Vinci probably sketched on paper before putting paint to canvas.

For the study, Cotte used a multispectral camera of his own invention. (Da Vinci would appreciate that!) He also used his own “layer amplification method” (LAM). It allows researchers to spot hidden reflections under many layers of paint.

The multispectral camera reveals “very fine details,” according to Cotte. His analysis showed faint charcoal lines under the centuries-old paint.

God doesn’t need a special camera to see hidden things. To Him, “all things are open and laid bare.” (Hebrews 4:13 NASB) This can be frightening for those who hide under layers of good works or self-worth. But it is freeing to those whose righteousness is in Jesus Christ alone!

The lines Cotte found reveal a drawing technique called spolvero. It involves pricking tiny holes around a sketched outline. An artist then rubs charcoal dust on the back of the sketch. By pressing the pricked and blackened sheet onto a canvas (or some other item), the artist can make a simple copy of the work.

“The spolvero on the forehead and on the hand betrays a complete underdrawing,” Cotte says. The discovery is the first proof that da Vinci sketched first and made changes for the final painting.

Cotte’s research revealed other surprising details. For example, the LAM shows a mass of curls atop the smiling lady’s smooth hairstyle. A squiggle that looks like a hairpin hides in the midst of the ringlets. Further underdrawing shows adornments to the woman’s costume and the chair she sits in. Why the Renaissance master made changes, no one knows. But it shows that even great artists feel the need to plan and practice.

The underdrawing could also mean that da Vinci made more copies of the painting. Some experts believe both the Prado Mona Lisa and the Isleworth Mona Lisa are such copies.

But perhaps most importantly for art fans, the spolvero discovery gives hope that somehow, somewhere there is an original paper sketch of the Mona Lisa done by da Vinci himself.