With his own knowledge of chemistry and metallurgy, as well as the help of chemist Paul Beck Goddard, Cornelius attempted to perfect the daguerreotype. Around October 1839, at age 30, Cornelius took a self-portrait outside of the family store. The daguerreotype produced is an off-center portrait of himself with crossed arms and tousled hair. While Louis Daguerre's photograph of the Boulevard du Temple, taken one year earlier, incidentally included two human figures on the sidewalk, Cornelius' photo is the oldest known intentional photographic portrait of a human made in the United States. It was preceded by at least some months by portraits taken by Hippolyte Bayard in France. The quality of the photographic plate and the technique used required him to sit motionless for 10 to 15 minutes.