In his paintings and collages, which often incorporate images from mythology, fables, symbols, chemistry, or alchemy, Jess created absurd and complex pictorial worlds. He took the name “Jess” after separating from his family in the late 1940s. While studying chemistry at the California Institute of Technology, he was drafted into the U.S. Army in 1943 and was assigned to the Army Corps of Engineers and worked at the Manhattan Project in Oak Ridge, Tennessee, on the production of plutonium for the atomic bomb, until 1946. After completing his degree in radiochemistry he began to study painting and to question his involvement with nuclear energy. He enrolled at the California School of Fine Arts (now San Francisco Art Institute) in 1949, where he studied with Abstract Expressionist Clyfford Still (1904–1980) and figurative painter Elmer Bischoff (1916–1991), among others, and had his first solo show at the Helvie Makela Gallery, San Francisco, in 1950. Throughout the 1950s he experimented with narrative and technique in still lifes, portraits, and landscapes, some of which he likened to creation myths. During this period he also began making collages, which he called “paste-ups”; works from his “Translation” series (begun in 1959) incorporated literary texts.