One of the tops in the trade

For Tony Gardner, a 21-year veteran of movie makeup and special effects prosthetics, the request was hardly unusual. “We want you to put some massive fake breasts on Selma Blair,” he recalls John Waters telling him by phone. “Boobs that toe the line of decency and physical plausibility.”

When Gardner stopped laughing, he took the job on “A Dirty Shame,” the raunch-friendly director’s NC-17-rated sex farce that came out on Friday. The prosthetic designer’s primary directive: Transform the gamine Blair into an exhibitionistic exotic dancer whose stage name, Ursula Udders, bespeaks her monumental physique. “John said he wanted to get these as large as we can -- but not just be boobs on legs,” Gardner says.

After experimenting with the size and shape of her appendages -- initially, kickballs were used as stand-ins -- he faced the difficulty of his appointed task. “We figured out the plane in between the boobs , as well as the mass and angle they would lie at,” he says. “Plus, I learned the relationship between the fullness, circumference and cup size.

“All of a sudden, there were all of these technical aspects. That’s when the fear factor set in.”

But it wasn’t the first time he had been enlisted to grossly distort female anatomy. The designer’s more notable professional achievements include the shriveled geriatric breasts shown to hilarious effect in “There’s Something About Mary” and Gwyneth Paltrow’s “fat suit,” which simulated her appearance as a 375-pound woman in “Shallow Hal.” More of his work will be featured later this year in “The SpongeBob Squarepants Movie” and “Seed of Chucky.”

To help facilitate Gardner’s work on “Shame,” Waters’ office faxed him pages from breast fetish magazines and e-mailed him websites where he could research the sex performer Zena Fulsom. “She’s this English porn star with breasts bigger than her head,” explains Waters.

“I always wondered about women that have [breasts] like that. How do they do normal things? Like go to the dentist or the Department of Motor Vehicles? That’s what gave me the idea.”

But the construction of such breasts involved a higher degree of technical expertise than anyone had imagined. Six pairs were constructed out of materials such as foam latex, urethane rubber and balloon rubber, while the custom latex breasts used for Blair’s nude scenes required a lengthy application process that would begin on her shooting days at 4 a.m. Other nonprosthetic “stunt breasts” functioned like bustiers, allowing the actress to slip them on and off easily -- even if they resulted in some unusual side effects. “She couldn’t see her feet, couldn’t tie her shoes,” says Gardner, 40. “She couldn’t put on a bathrobe or cross her arms in front of her face.”

Size wasn’t the only thing that mattered to Gardner, who describes his major innovation on the project as “layers of water balloons.” “There’s a hollow air cavity surrounding an internal cavity filled with liquid inside the breast,” he says. “That way it would hold its weight but still follow through -- but without being so much weight that she couldn’t do what she needed to do.” (In Blair’s character’s case, that meant activities including go-go dancing on rooftops and pole dancing in a dive bar.)

Although the actress was impressed by the way her prostheses stood up to the physical demands of her role, the fakes never prompted a case of chest envy.

“I’m not a large-breasted girl, to say the least,” Blair says. “But for people who have no idea these enormous breasts aren’t real, they’ll be like, ‘Oh, that poor girl! She must be deformed.’ ”