In 2018, the Mauritshuis gallery in The Hague, Netherlands, gathered an international team of researchers to take part in its “Girl in the Spotlight” project, which aimed to unlock the secrets of Johannes Vermeer’s famed Girl With a Pearl Earring, circa 1665.

Their recently published findings reveal many intriguing details about Vermeer’s artistic process and the artwork itself, though the identity of the painting’s enigmatic subject remains a mystery. Using X-rays and other advanced imaging techniques, the researchers discovered Vermeer depicted the girl in front of a faint green curtain—not an empty dark background—and even painted eyelashes on her eyes.

As The Guardian reports, scholars in the past have cited both the lack of eyelashes and the blank background as support for the theory that Vermeer was painting a conceptual, idealized image of a girl, so these newfound features could be evidence that an actual person posed for him in a specific setting. And, according to head researcher Abbie Vandivere, it’s not entirely a bad thing that we still don’t know who that person is.

“It is good that some mysteries remain and everyone can speculate about her. It allows people their own personal interpretation of the girl; everyone feels their own connection with the way she meets your eyes,” she told The Guardian. “The fact that she is still a mystery keeps people coming back and keeps her exciting and fresh.”

While we’re all pondering the puzzling origin of one of the most captivating models in art history, there are plenty of other fascinating revelations from the Mauritshuis investigation to talk about, too. For one, the Dutch artist evidently spared no expense in bringing Girl With a Pearl Earring to life: the raw materials he used to create various colors in the painting came from just about everywhere, including England, Mexico, Central America, and maybe even Asia or the West Indies. Ultramarine, a blue pigment derived from lapis lazuli (an export of what’s now Afghanistan), which Vermeer used for the girl’s headscarf and jacket, was more valuable than gold at the time.

The study also shed light on Vermeer’s painting methods. He began with broad brush strokes of brown and black paint, layering the girl on top of the background, and then made slight adjustments to her ear, the back of her neck, and the top of her scarf.

If “Girl in the Spotlight” has proven anything, it’s that there’s always more to discover about a work of art—and that’s just what the Mauritshuis intends to do.

“Please know that this is not the end point of our research, but an intermediate station,” Mauritshuis director Martine Gosselink said in a press release. “The collaborations are growing, and so is the desire to find out more.”

As you wait for more information to come to light, here are 15 fascinating facts about Girl With a Pearl Earring.

[h/t The Guardian]