Flashing/Pulsating 10mm Red LED voltage

I just finally got the throbbing/flashing/pulsating LED, but a 9v battery doesn't seem to be cutting it. I bought the 10mm LED from Radioshack here. I was just wondering how high I could go in terms of power. I was thinking about a 10v DC, and go to a 12v. But I don't want to blow the LED. I was also wondering how I can get the LED to flash slowly, like it was "breathing". I started off with a 1000µf 16v capacitor, then went down to 470µf 25v capacitor, with no significant change. I also have a 470ohm resistor that I got with my 100 pack of white LEDs. Any recommendations would be appreciated.