Senior conservator of paintings, Ann Hoenigswald is interviewed in front of X-ray images of works by Frederic Bazille at the National Gallery of Art. Hoenigswald has been investigating some paintings by Bazille. (Matt McClain/The Washington Post)

While visitors to the National Gallery of Art’s new Impressionist exhibit see lush landscapes and intimate portraits, conservator Ann Hoenigswald spots clues involving an artist fixing mistakes and evidence of earlier compositions hidden underneath.

Like a detective, the National Gallery’s senior conservator of paintings compiles these observations, which later guide her work in the lab, where high-powered instruments can uncover more about the paintings and the artists.

Her sleuthing skills are in high gear with “Frédéric Bazille and the Birth of Impressionism,” the critically acclaimed exhibit on view through July 9. Hoenigswald was in Paris last year with curators from the three museums that collaborated on the exhibition — the National Gallery of Art, the Musée Fabre in Montpellier and the Musée d’Orsay in Paris — who discovered an important Bazille work under “Ruth and Boaz,” a later painting by the artist. Examining X-rays of the large work alongside the painting itself, they pieced together the elements of “Young Woman at the Piano,” a work that had been thought lost.

“In a number of ways, this was the biggest prize,” Hoenigswald said. “He had written so much about the [hidden painting], so we know how important it was to him.”

Hoenigswald will build on this research in July, when the exhibit closes and she can take some of the paintings into her lab.

“Recognizing that the hidden pictures appear so often establishes a pattern and identifies how the artist worked,” Hoenigswald said. (Matt McClain/The Washington Post)

“The individual images make more sense when you see them within the larger picture,” she said. “Each one alone is interesting, but . . . recognizing that the hidden pictures appear so often establishes a pattern and identifies how the artist worked.”

A 19th-century contemporary of masters such as Claude Monet, Auguste Renoir and Édouard Manet, Bazille left his upper-middle-class family in southern France for Paris, where he studied both art and medicine. While taking painting lessons, he became friendly with Renoir, Monet and Alfred Sisley, artists whose work is included in the exhibit. Bazille shared studio space with several of them, and letters show they helped one another purchase pigments and canvases. Several of Bazille’s paintings focus on the studio and the creative life of the artists.

Bazille died at age 28 in the Franco-Prussian War, leaving behind only about 60 works. About 46 of his paintings are featured in the exhibit, the most comprehensive retrospective of his career and the first in the United States in a quarter-century. Museum curators and scientists have discovered at least 11 of his paintings have earlier compositions underneath — a considerable number for such a modest output.

“We definitely expect to find more pictures, and learn more about his process and about his relationships with fellow artists,” Hoenigswald said.

They have learned a great deal already. Scans have revealed that Bazille frequently reused canvases, probably to save money. He often rotated the works 90 or 180 degrees, Hoenigswald said, but he worked without obscuring the previous work with a new ground layer of paint or scraping off the earlier pigment.

“He’s not forgetting what’s underneath,” she said. “It’s extraordinarily difficult, disruptive, like white noise. He chose not to eliminate it, [so] he must have been getting some sort of inspiration.”

Frederic Bazille. "Young Woman with Peonies," spring 1870, oil on canvas. (National Gallery of Art, Washington)

As an example, Hoenigswald points to “Woman with the Peonies.” She can see where Bazille allowed the elements of a previous work to become the shadows of the flowers in this image.

Most of the earlier works are revealed only through scientific scans, but there is one that allows viewers to see the work underneath. Bazille’s “Study for a Young Male Nude” is painted on the top half of a large canvas, over an earlier composition featuring the skirts of two women.

“This is better than seeing an X-ray,” Hoenigswald said, studying the canvas in the gallery. “Who is the artist? What are the colors?”

She and her technicians will use a variety of scans, including infrared and X-ray fluorescence, to analyze this canvas and a few others. They will build a library of technical images of what’s underneath the surface, and working with his drawings and letters, she thinks they will uncover even more information.

A photograph of Frederic Bazille's painting of Edmond Maitre from 1869 is part of a new exhibit on Bazille at the National Gallery of Art. (Matt McClain/The Washington Post)

“The National Gallery has instruments and expertise that other museums don’t have. We have this opportunity to do this work and share the findings,” she said. “To look at so many pictures simultaneously, and in the context of [his] drawings . . . will enhance our understanding of Bazille’s process and technique.”

Hoenigswald will have only a few weeks to research the paintings before they must be returned to their partner museums. To prepare, she will talk to the curators here and in France to create a list of priorities for the National Gallery lab.

“I’ll spend a lot of mornings in the gallery to figure out what we will do,” she said, smiling. “The more you look, the more you connect the dots.”

Frédéric Bazille and the Birth of Impressionism Through July 9 at the National Gallery of Art, Sixth Street and Constitution Avenue NW. Free. 202-737-4215.