WASHINGTON – George Washington is about to get a long-awaited facelift.

Gilbert Stuart’s full-length portrait of the nation’s first commander in chief at the National Portrait Gallery will be taken off view at the end of the month so conservators and curators can study it – and maybe make it look better.

A centerpiece of the Smithsonian museum’s “America’s Presidents” exhibition, the 1796 portrait will be analyzed and treated by the museum’s conservation experts. The project is expected to take 18 months.

“It is an icon, and it demands a tremendous amount of respect. Hopefully, we will bring it back to its original brilliance,” said Cindy Lou Molnar, head of conservation at the National Portrait Gallery.

The painting is known as the Lansdowne portrait because it was commissioned as a gift for the Marquis of Lansdowne, an English lord who supported the American Revolution. One of Stuart’s best portraits, the 8-by-5-foot work shows Washington not as a general, but as head of state, surrounded by symbols of the American republic.

“It’s the only life-size, full-length portrait of Washington showing him as president,” said curator emeritus Ellen Miles. “The size, the complexity of the composition, it is a life achievement for Stuart.”

The work depicts a rosy-cheeked Washington in a black velvet coat, his left hand resting on a ceremonial sword, his right arm held aloft in a welcoming gesture.

While the Lansdowne is being analyzed and treated, the gallery will display a 1790-1792 portrait of Washington by Charles Willson Peale, on loan from the Crystal Bridges Museum of American Art in Arkansas.

After the Stuart painting is removed from the gallery Feb. 29, it will be taken to the Smithsonian imaging laboratory. There, various scans will document its condition. The X-rays could show any changes Stuart made and whether he did any sketching on the canvas before he began to paint, a technique called underdrawing that he did not typically employ. The infrared images will reveal multiple layers of paint and perhaps uncover plans he abandoned or changes he made.

The ultraviolet imaging shows the surface, allowing Molnar to make a plan to remove the varnish and improve the “mottled” area of his black coat. She will also use a microscope to “look deep down into the crevices of the paint.”

When the analysis is complete, Molnar will work on the canvas to remove the varnish and fill in any losses that are found. She will apply a protective varnish at the end. It is a painstaking process, with the conservator focused on one-quarter inch at a time.

She will work in the museum’s Lunder Conservation Center’s glass-enclosed lab, and visitors may catch glimpses of the effort.

Molnar has devoted her career to painting conversation and has worked on similarly valuable and important works. She described her approach in measured tones, declining to say whether she will be nervous as she begins the treatment. Rather, she said, she is focused on what might be learned about the painter and his process.

“Getting a person and all the elements of a full-length portrait is a compositional challenge,” she said. “This was his first full-length portrait of George Washington, and he was working through the process and we’re seeing him do it.”

Miles, too, is excited about the potential to make discoveries in the lab. “Stuart didn’t leave us many documents explaining what he was thinking,” she said. “Are we going to learn something from this? “