Transforming a well-known actor into a well-known political figure on the screen is tricky business. The visual familiarity with both can be a huge challenge, leaving viewers scrutinizing the work more than they might otherwise.

In the case if “The Iron Lady,” one of the most recognizable actresses in the world, Meryl Streep, had to undergo such a transformation as prosthetics designer Mark Coulier and hair designer Marese Langan were tasked with turning her into former British Prime Minister Margaret Thatcher. But beyond just the physical transformation of one visage into another, “The Iron Lady” is a decades-spanning effort that sees a gradual shift in appearance for the character throughout the movie.

And even then, it wasn’t just a single actor undergoing this kind of work. “We had a cast of 70 playing mostly historical characters,” says Langan. “Therefore we had to give a nod towards the physical appearance of these real-life figures, and in many cases, this required the use of wigs and hair pieces.”

Langan, who trained for hair and makeup (which are seen as one department in the UK) at the Delmar Academy, says she owes her inspiration in the field to Tom Smith, a former teacher who developed techniques for such films as “Gandhi” and the Indiana Jones franchise. She says one of the biggest challenges on this film was bringing together the look of Streep’s character seamlessly over a large span of time.

“Without the use of wigs and hair pieces, it would have been impossible to accurately define a period,” she says. “It is also an invaluable way to show changes in age and character. On this particular project, we used a large amount of hair pieces and hair wefts rather than full wigs on the politicians. These worked really well in creating a natural look and eliminated some of the problems that can be associated with wigs. It was great to see how well the prosthetics worked; the different techniques and products are ever-changing in this field.”

Those prosthetics were tasked to Coulier and his team. He says with a film like “The Iron Lady,” his work is in pretty much every single shot of the film, meaning it is under a lot of consistent scrutiny. But he’s proud of the aging work in particular, which he notes is always a challenge to do realistically.

“It’s difficult to have it move well and very easy to get wrong,” he says of the applications. “Although the fact that people have not realized quite what prosthetics some of the other characters are wearing is also quite rewarding. If our work goes unnoticed, I take that as a compliment.”

Another nominee in the field, “Albert Nobbs,” has also been championed by fellow makeup artists for its invisible nature. The third nominee, however, “Harry Potter and the Deathly Hallows: Part 2,” is an example of more severe, fantasy makeup work, indicating the range of quality the branch scrutinizes during the awards season each year.

Getting back to “The Iron Lady,” Coulier also notes of the consistency of his work on screen how hard it can be to maintain during a lengthy work day. “It is very difficult to maintain makeups like this during a 14-hour shooting day on very hot sets when characters are involved in lots of close-ups with intimate detail,” he says.

Streep herself had very strong ideas about what she would like to see and what strength of character the makeup team should bring out of Thatcher, Coulier says. It was a process of boiling down what they could enhance of the actress’s features and what they needed to change. “We really did see eye-to-eye during this process,” Coulier says of the collaboration, “never wanting to go too far with prosthetics and have them be too much of a talking point.”

On that note, one of the contenders in the field this year, another film built on transforming a famous actor into a famous politician — Clint Eastwood’s “J. Edgar” — suffered from that kind of scrutiny and ultimately failed to even make the bake-off list of seven finalists.

The job of a makeup artist is incredibly collaborative, not just with the actor and director, but with the cinematographer. Indeed, the design elements of a film can be the most beautifully and carefully rendered, but it’s all for naught if they aren’t properly captured on film.

“Elliot Davies, the Director of Photography, did a beautiful job of lighting the makeups,” Coulier says. “It is especially tricky to correctly light prosthetics so that it enhances their qualities and makes them look as real as possible and Elliot did an amazing job.”

The film is also nominated for Best Actress this year for Meryl Streep. It could turn up a surprise winner there, but it’s looking like the frontrunner here. Curiously, though, while Langan was the only nominee listed at the BAFTA awards (which include hair in the category), only prosthetics designers Coulier and J. Roy Helland are included for the Oscar. Go figure.

“The Iron Lady” is currently playing in theaters nationwide.

For year-round entertainment news and awards season commentary follow @kristapley on Twitter.

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