The actor - who plays J. Edgar Hoover's right-hand man Clyde Tolson in the biopic - shrugged off press criticism of the film, describing its make-up as "incredible".
He told USA Today: "The make-up, for what it was, was incredible. It was prosthetic make-up, done in the way you would have done that make-up 50 years ago. It's a throwback. It's nostalgic.
"No one does make-up like that anymore because it doesn't look the best, because it's not the cheapest and it's not the fastest. Clint [Eastwood], could have done it in CGI, and any other director immediately would have done it in CGI because it would have been easier, cheaper, the whole thing."
Hammer's character ages from a man in his 20s to a man in his 70s during the course of the movie. He went on to liken the make-up process to the effects used in classic horror movies such as Frankenstein.
"Clint's people and the people who did it are the very best at what they do. But it's an old way of doing make-up. I don't think many actors will get the chance to do that ever again. The fact that I even got a chance to participate in something like that was awesome."
J. Edgar, which stars Leonardo DiCaprio in the title role, is released in the UK on January 20, 2012.
> Leonardo DiCaprio: 'I hope I'm not recognisable in J. Edgar'
> Leonardo DiCaprio 'took 90% pay cut for Clint Eastwood's J. Edgar'
Watch a trailer for J. Edgar below: