Steven Spielberg and Jared Harris discussed Daniel Day-Lewis’ exhaustive preparation for his role as Abraham Lincoln for the film Lincoln, which opens today:

To hold on to Lincoln’s voice, he used it all the time, between takes and even after the filming was over. Mr. Spielberg said he couldn’t remember for certain whether Mr. Day-Lewis used his Lincoln voice in their private conversations but then added: “I just came to see him as the character. I assume he didn’t change the voice. Why would he?”

Jared Harris (better known to most Americans as Lane Pryce in “Mad Men”) plays Ulysses S. Grant in the movie. He recalled that like other British cast and crew members on the set, he was asked not to throw Mr. Day-Lewis off by speaking in a British accent, so Mr. Harris too stayed in character.

“It was sort of an extended improvisation,” he said in a telephone interview. “You didn’t go up to him and say, ‘Hey, did you see the Pirates game last night?’ It was important for him to retain the attitude, if you like, and the dialect he had created. So we would sit there and joke, for example, about the Vicksburg campaign.” He added, “At the end of the day sometimes we’d ride back in the car, and he’d stay in character but talk about ‘Mad Men,’ which of course he couldn’t know about, because television hadn’t been invented then.”