While recording her upcoming album "Back to Basics," a project inspired by music and images from the '20s, '30s and '40s, Christina Aguilera had a secret weapon -- bright red lipstick as shiny as a fire engine.

"Just to get into the song," she says, "to convey that emotion and high energy, especially to belt out some notes, the red lipstick helped me get to that mind frame."

Saluting artists from the past was a role Aguilera was born to play. Since her RCA debut seven years ago, the 25-year-old has talked about her love for such torch and blues singers as Etta James. As she prepared for the album, due for release August 15, "I would surround myself with old imagery of your Billie Holidays and your Pearl Baileys and people like that," she says.

Those photos accompanied her into the studio, as did "tear sheets and pictures of Louis Armstrong and (John) Coltrane and Miles Davis. I just wanted to get into the heart and soul of the music, literally. Actors call it 'method acting.' It was my way of method singing."

Aguilera's vision for the album was born from a poem she wrote while on her last tour. "I was like, 'What is it that really makes me want to sing? What is it that makes me want to dance? What makes me love and enjoy music?' And it's really that old blues and soul and jazz music -- music that really had heart. Not to say that music today doesn't have heart, but it's really few and far between, because technology has advanced itself so much that anybody can be a singer. Back in the day, you had to know how to sing."

LETTER TO PRODUCERS

With the new two-CD, 22-song set, executive-produced and co-written by Aguilera, her aim is no less ambitious than to pay homage to her musical heroes while inventing something completely new. The first disc, primarily produced by DJ Premier, combines old-song sensibilities with hip-hop elements, samples and modern technology.

Disc two, produced by Linda Perry (with whom Aguilera most famously collaborated on "Beautiful"), features all live instrumentation with no samples: Old-timey sounds were captured using vintage microphones sometimes covered with cloth to get a muffled effect.

Aguilera solicited producers for the album via a letter explaining her vision. Also enclosed was a compilation of more than 30 songs spanning the '20s through the '60s that had influenced her, including contributions from Otis Redding, Millie Jackson, Ray Charles, Nina Simone, Eartha Kitt and even Screamin' Jay Hawkins.

"I sent (the letter) out to producers that I thought might be able to get into this world with me," she says. "I wanted to get obscure pieces of music and get people who would really, really use their imaginations in creating something new. I didn't want any covers." She encouraged producers to take the songs on the CD and "chop things up, feel free to experiment."

In February, Aguilera called a Los Angeles meeting with her team at RCA to play portions of her record and to express her desires for "Back to Basics."

"I said, 'I want to be very hands-on in all the meetings that we take and the decision-making, because I'm very specific in my vision of this record,"' she recalls. "I wanted to start putting (the music) in their heads so they had time to brainstorm." She stressed a continuity that would run through all facets of the project from the songs, imaging, videos and touring that would combine the music with visuals that were a "throwback to old Hollywood glam, that kind of old, retro, pinup style of sexuality."

BAD TIMES

Aguilera's deep level of involvement in all facets of her career is spurred by her own admitted workaholic tendencies ("I feel like I always need to work," she says) and also borne from past bad experiences. "The first record was an uphill battle for me, and I really feel like I paid my dues on that first record. Being part of a huge pop explosion, I was very pushed by the label to be, act, dress a certain way, and it was tough."