The scene is both iconic and misleading. The hats at Royal Ascot were rarely black and white. But when famed costume designer Cecil Beaton depicted aristocrats in achromatic ensembles for the film adaptation of “My Fair Lady,” he introduced American audiences to Britain’s most prestigious racing event, one where opulent, outrageous hats are more important than the horses.

That’s why the Ascot scene is both a challenge and thrill for Arena Stage’s craftsperson and milliner Deborah Nash. Audiences may expect a spectacle of black-and-white Victorian lace, but at Arena Stage’s upcoming production of “My Fair Lady,” opening Nov. 2, they’ll see a tropical palette of emerald greens, royal blues and rich burgundies, a more realistic portrayal of the topsy-turvy hats on display at Royal Ascot.

“This is a definitely a career highlight,” Nash said. “This will be the largest amount of hats for any show we’ve ever done.”

“These are the plums,” said Arena Stage’s costume director Joe Salasovich. “These are the projects that you hope you to get to do, because they’re eye-catching. But it still has to be sincere to the story. The actor has to wear it with ease.”

And this colorful surprise (now spoiled) is not easy scene to achieve. Arena Stage’s take on the Ascot scene, imagined by “My Fair Lady” costume designer Judith Bowden, features 11 handcrafted hats by Nash, many of which took more than 30 hours of labor each to create.

But if anyone can outfit stands of racegoers with gasp-inducing headwear, it is Nash, one of Washington’s most prolific milliners. Nash has perfected the processes for building an accessory that is no longer required in even the most formal of American settings. But her talent is in demand in the theater, having made hundreds of fascinators, top hats, strip-straw hats, driving hats and turbans in her roughly 13-year career at Arena Stage. She doesn’t rest, even in the off-season. During the summer, she drives to New Mexico to make hats for the Santa Fe Opera.

Nash has produced enough peaks, points and frills to outfit the entire congregation for a Westminster Abbey wedding. She made the strip-straw hats for the ladies of “Oklahoma!” The Peking Opera headdress for “M. Butterfly.” Nash once fashioned a hat with a built-in tissue box for Adelaide of “Guys and Dolls,” poi-fect for poi-sons with bad, bad colds.

Few area theaters have a milliner with such range: and hats, particularly in musical theater, play an important role. Situated near the actor’s face, where the most memorable action happens, hats must complement the story line on the stage without distracting the audience, actors or dancers.

Her hats verge on fantastical — her favorite hat is from “The Women” and contains a vulture’s head she made from plaster that sits amidst a nest of black feathers. They must weather years of wear that theater costumes inevitably endure.

And they are archived for history, or at least saved in stock for successive shows that might call for fascinators, top hats or bowlers. Many of Nash’s creations are kept in the Mead Center for American Theater’s massive hat library, a part of their costume shop with racks filled with hats created by Nash or other technicians, as well as vintage hats donated period hats from as early as the 1890s.

Salasovich acts as the costume shop’s librarian, using only his acute memory to spout off the details of each work: the actors who wore them, the scenes from the shows they came from, the materials used to make them.

“We have things organized loosely,” Salasovich said. “There’s no card catalogue. The space was built so we could expand into it, but within six months a woman donated a whole vintage store worth of hats. So we’re at capacity now.”

And there’s more hats on the way.

For “My Fair Lady,” Nash faces her most massive project yet: She will make, deconstruct, embellish or touch up a total of 85 hats, 11 of which will appear on the women at those “absolutely thrilling” races. While some the men’s top hats were ordered or pulled from stock, she will make sure each is stage-ready. The women’s hats are the most time-consuming. She had only nine weeks to prepare, and only a few weeks before the show’s debut, not a single hat was completed.

“I move all the hats forward at the same pace,” she said. “I rarely finish one and move on to the next. . . . It’s a little daunting, but I’m used to dealing with large quantities.”

And she is used to the exhausting pace: the gripping, ripping, and smashing of materials into dashing concoctions that have become a hallmark of Arena Stage’s impressive costume shop. Indeed, the ensemble production that occurs behind the scenes, one performed by a small cast of talented technicians and designers who toil away for months, may be as dramatic as the show itself.

“People aren’t going to know what hit them with the Ascot hats,” Salasovich said. “They will be among our greatest.”

And they’re off . . .

The hatmaker’s lair, or craftsroom at Arena, contains molds, fabrics, color swatches, and “The Bible,” what Salasovich and Nash affectionately call the book that contains notes on every piece in the entire show.

The process for hatmaking is deceptive because the early stages require elaborate pieces the hat-wearer never sees: the sketches of the design, cardboard 3-D mock-ups of the hat, a mold of the wearer’s head, circumference precisely measured. There are multiple fittings and blocks are amended to precision so the hats are custom-made for the actor wearing them.

For Eliza, Nash built a mold of actor Manna Nichols’s head from insulation foam and built Eliza’s sea foam green hat around it. She used clay to round out the shape of the head to achieve Bowden’s design. Sometimes the hat blocks are made from industrial felt that is stiffened and wired, so materials can be pulled over the mold to achieve precise shapes.

When building the Ascot hats, Nash had to work with negative space, since much of the hat will rest on the wigs the actors wear. She also had to consult the wig designers and sound designers, since the hats contain microphones and sound equipment.

The hats at Ascot are made of Sinamay, a malleable material from the Philippines that becomes stiff and straw-like when molded. It’s an ideal material: sturdy enough to weather time and survive frantic costume changes that occur between scenes.

The Sinamay is dyed to meet Bowden’s exact color requirements for the scene.

“I probably spent a day and a half dyeing swatches,” Nash said. “We use an industrial soup kettle to dye all our crafts, and the dye is mixed to achieve precise shades.”

Nash made hundreds of swatches of different shades of red, blue, yellow; Bowden, who designed all the costumes for the show, chose the colors she wanted.

“When you work this close and intensely on a project, you develop a vocabulary,” Nash said. “Part of working with new designers is learning their vocabulary, so when they say ‘dye this cream,’ you know what they mean by ‘cream.’ ”

After the blocks are built and materials are dyed, the mock-ups of elaborate shapes and styles are constructed. The design goes from 2-D to 3-D.

Nash notes that she doesn’t build every hat from scratch. Many are deconstructed from old hats, or made to look old. She often buys vintage ones and uses the linings to create new works. Materials come from everywhere, with Salasovich saying “No straw place mat is safe around us,” since the straw in place mats is perfect for constructing strip-straw hats.

“We’re constantly making old things look new, and new things look old here,” Salasovich said.

After the 3-D construction of the hat, it is embellished, with some of Nash’s most elaborate pieces involving metalwork, ostrich feathers, Swarovski crystals, and multiple fabrics.

Nash doesn’t sugarcoat the complicated, time-consuming process.

“Every hat is difficult in its own way,” she said. “Eliza’s hat will take more time because I had to create a block for it. But each production presents its own challenges. You’re never building a hat the same way twice.”

Brimming with knowledge

Nash was the child who couldn’t sit still, building and tinkering and breaking things constantly. Born in Nebraska, she moved to Baltimore at age 6 and considers herself a local. Her parents realized her flair for the arts, and sent her to Baltimore School for the Arts, a public magnet high school renowned for its intensive arts program. But there, she began studying violin, not design.

She credits her grandmother with having the good sense to teach her to sew one summer.

“I just fell in love with it,” Nash said. “By sophomore year of high school, I was cutting class to go to costume shop.”

Her teachers encouraged her to change her focus from music to design, and she gladly gave up the bow for the sewing needle. She then attended Boston University, where she majored in costume design and took intensive courses on millinery, a skill she’d dabbled in while in high school but came to love in college. She landed her first job out of college at Arena Stage and has been there ever since, except for the one-year sabbatical she took in 2006 to study millinery at Kensington and Chelsea College in London.

“They have so many more resources in Britain,” Nash said. “So I worked with some milliners who worked with the big fashion houses, and also theatrical milliners for ‘Harry Potter’ or BBC.”

There she learned new techniques, a necessity for milliners since traditional materials are becoming scarce. But modernizing millinery is not necessarily bad — at the turn of the century, milliners used materials that contained mercury.

“There was some truth to the Mad Hatter,” Salasovich said.

As for learning the trade, Nash says it’s important to apprentice.

“It’s so important to find someone to study under,” Nash said. “I have some great books from the ’20s and ’30s, but the materials don’t exist anymore. Or the techniques are dated. One book recommended washing feathers in gasoline. We wouldn’t recommend that today.”

Salasovich says that’s one of the great joys of Arena Stage: the apprenticeship culture it fosters. Nash has taught many technicians and apprentices her tricks.

“In terms of the artistry going on here, there are a lot of people at the top of their game,” Salasovich said. “For me, I’m honored that I get to work with Deborah or the patternmakers who have been in the costume shop for over 20 and 30 years. It’s one of the cool things about Arena. There’s longevity, and we’re passing down techniques.”

My Fair Lady

at Arena Stage, Nov. 2-Jan. 6. 1101 Sixth St. SW. 202-488-3300.