Byron Kim crouched on a small tarp unfurled in the middle of the atrium at the National Gallery of Art’s East Building, studying NGA housekeeper Leora Wilson’s skin and a dab of oil paint he had mixed to a precise match.

Then the Korean American artist moved on to painting conservationist Jay Krueger, art handler Joan Ganzevoort and museum educator Deirdre Palmer. He spent about 30 minutes with each of the 10 sitters, creating a “skin painting” for his continuing work “Synecdoche.”

A modern take on portraiture, Kim’s work explores the meaning of individual and collective portraiture, as well as issues of race, representation and identity. The title comes from the figure of speech in which a part stands for a whole, and vice versa.

The National Gallery of Art acquired “Synecdoche” in 2009, and it was on view until the East Building was closed for renovation in 2013. After the work was taken down, Kim and contemporary art curator Molly Donovan discussed adding to it before it went back on view this spring. Kim loved the idea, but procrastinated.

Then Donald Trump was elected president.

“This work has come to recognize a kind of inclusiveness, which I didn’t expect when I first made it,” said Kim, 55. “It’s really important to keep our mind on that idea of including everybody, especially now.”

The work features about 400 panels, each 8 by 10 inches in a nod to a typical photographic portrait, and each representative of the skin tones of strangers, friends, fellow artists and Kim himself. And last week, NGA employees, many with direct connections to the work, volunteered to sit for him.

“It was amazing. I was mesmerized to see how he worked the colors,” Palmer said before listing the pigments — blue, green, yellow, a dab of black and a little lavender — that Kim blended.

Kim first created the piece in 1991, and it made a splash at the 1993 Whitney Biennial.  “I was making a statement about modernism,” Kim said, thinking back to its beginnings 26 years ago.

With padded knees and sitting on a yoga block, Kim mixed the paints with his palette knife before applying a bit to a piece of tape affixed to each sitter’s forearm. He’d mix, then dab it on the sitter’s arm, then squint at the match, often removing his glasses as he moved within inches of the model.

Crowds gathered in a semicircle, and visitors and guards peered down from the overhead walkways. No one interrupted the artist, who chatted quietly with his models as he worked. When he was satisfied with the match, he wrapped the gob of paint into a paper pouch and wrote the name of his sitter on it. He will paint two panels from each hue when he returns to his New York studio.

Donovan called the piece a “watershed” work for the artist and a significant part of the gallery’s collection.

“It’s about individual and collective portraiture, and it relates to our collection in a very meaningful way,” she said. “It relates to our Renaissance portraits, and then fast-forward to the modern era and the idea of monochromatic panels and Ellsworth Kelly’s ‘Color Panels for a Large Wall.’ ”

Julie Springer, manager of teacher programs, has used the work in her lessons and was delighted to participate in its evolution.

“It’s so powerful,” she said. “It’s about racial identity and what is identity. It’s like ‘e pluribus unum.’ ”