Researchers used super-X-ray vision to peer beneath the surface of a portrait by impressionist Edgar Degas and gaze upon the model whose likeness he painted over nearly 140 years ago, they reported Thursday.

The woman, whose image Degas turned upside down before using it as a base for a new painting, was probably Emma Dobigny — a favourite model of 19th century French artists, the team announced.

“This has been a very exciting discovery,” said David Thurrowgood, conservator at the National Gallery of Victoria, Australia, where the painting hangs.

“It is not every day that a new Degas painting is found, in this case, hidden in front of us.”

The existence of the “underpainting” has been known since about 1920.

A vague, ghostly figure has been slowly emerging, spreading an increasingly dark stain over the face of the model that replaced her.

Enter the Australian Synchrotron in Victoria

But previous attempts to glean something about the jilted original yielded little more than a faint outline.

The hidden image “has long been considered to be indecipherable” without damaging the surface painting, the research team wrote in the journal Scientific Reports.

Enter the Australian Synchrotron in Victoria, a particle accelerator which generates radiation for high-resolution imaging in research, therapy, or forensic analysis.

The light it produces “is a million times brighter than the Sun, many orders of magnitude greater in power and intensity compared to standard, hospital-like X-rays,” synchrotron scientist and study co-author Daryl Howard told AFP.

“Because of the brilliant light, we are able to reveal unprecedented structural detail of any material”.

Using a technique called X-ray fluorescence, the team became the first people since Degas to gaze upon his model’s face.

Comparing the image to other paintings, they concluded it was likely “a previously unknown portrait of the model Emma Dobigny.”

Dobigny, whose real name was Marie Emma Thuilleux, modelled for Degas in 1869 and 1870 when she was about 16.