Disney hit “Mary Poppins Returns” not only successfully revisited the iconic look of the 1964 classic, it also brought back old-fashioned pencil-on-paper 2D animation to a Disney feature production.

For a 17-minute sequence in the movie, Emily Blunt’s Mary Poppins, Lin-Manuel Miranda’s Jack and the children Annabel and John enter a 2D animated world of a painting to meet dancing penguins, puffed-up hummingbirds, and stage the show-stopping song-and-dance number “A Cover Is Not the Book.”

Former Pixar story artist Jim Capobianco supervised the animation sequence for director Rob Marshall and entrusted the work to Pasadena-based Duncan Studio, one of a very few animation houses producing paper-drawn 2D animation in the CG age.

“It was amazing having a full team of people and literally hearing the paper flip,” says animation veteran Ken Duncan, Duncan Studio’s president and chief creative officer. “There’s something soothing about it. It’s pretty cool.”

Duncan assembled a crew that included 14 animators, 50 clean-up artists and about a dozen ink and paint people. All the animation and clean-up was done on paper. Even when work from artists abroad had to be done digitally, it was printed to paper for clean-up. Final pencil drawings were scanned into ToonBoom for ink and paint, and rough compositing in Adobe After Effects. Final compositing was done in Nuke, with vfx house Framestore doing final touch up and color tweaks.

“The big challenge was trying to put that crew together almost overnight,” he says. Finding enough animators with 2D paper experience who were available required using a few animators from Europe and bringing in a couple of artists from Brazil. For most, the chance to work on a sequel to “Mary Poppins” was a big draw, Duncan says.

Work began with Duncan’s crew heading to the Walt Disney Archives in Glendale to see original artwork, backgrounds and cels from 1961’s “101 Dalmatians” and the original “Mary Poppins.”

“Dalmatians” is significant for being Disney’s first animated feature to replace the process of having an artist trace finished animation pencil drawings in ink on a cellulose sheet by using then-new Xerox technology to duplicate and darken pencil drawings directly onto the cel. Eliminating that step saved enough time and money to keep animated features at Disney in the black and created a sketchier look that defined the era.

Keeping that look was important, Duncan says, but the vintage Xerox technology doesn’t really exist anymore, requiring the look to be added in After Effects.

Before pencil was put to paper, Duncan flew to London for live-action rehearsals and then three more times over a five-month period for the shoot.

Duncan, Capobianco and supervising animator Chris Sauve collaborated with Marshall, cinematographer Dion Beebe, production designer John Myhre and costume designer Sandy Powell to refine the sequence. Beebe had a knack for combining shots and finding more active camera movements, while Myhre designed the greenscreen stage down to the inch to facilitate the dancers’ performances and the animators’ needs, he says. Powell redesigned the costumes by painting them to look more “animated” after test footage showed a more realistic style meshed poorly with animation.

Duncan credits Marshall for the easy work environment. ”He really has a good appreciation for animation and he understood it,” he says. “He made sure everything was harmonious.”

Being on set also gave Duncan’s crew creative input. “For instance, in the hummingbird scene, rather than having them land on (Mary Poppins’) finger and then go, we would sort of advise, ‘Hey, it’d be nice to have a beat,’ because we knew we were going to animate some character stuff that they were not aware of.”

And while it wasn’t completely by design, Duncan’s crew was about 40% women. “I wanted more female animators, but in the hand-drawn paper animation era, there weren’t that many to begin with,” he says. New talent filled some of those gaps. “I’d say animation and compositing could use more women, and I think in the digital world, the CG animation, there’s a lot more women (than in 2D).”

Duncan shrugs off the common suggestion that digital is always the best solution. “If you know how to do it on paper, why not just do what you know?” he says. ”If I could play the violin, yeah, you could (create the instrument’s sounds) digitally, but isn’t it great to hear a real violin?”