Self-taught and inspired by Reynal's collection of abstract art, he began working with the materials he found in her mosaic studio, but soon branched out to oil on wood as well as canvas.
Sills spent most of his creative life in New York City, deeply rooted in the artistic trends as well as cultural issues from the early 1950s to 1970s.
[2] His friendships with Newman and Mark Rothko placed him at the intellectual center of the Abstract Expressionist movement, but like de Kooning, Arshile Gorky and Franz Kline, Sills believed that it was not necessary to explain his art; he painted what he felt and it came from within.
Sills' work was highly intuitive and he too sought inspiration from indigenous art—in the 1950s he made frequent trips to Mexico to study the sculptures, frescos and architecture of Chiapas and the Yucatan.
He would also travel widely around the world to Peru, England, Russia, France, Italy, Spain, and other countries, influencing his work.
His work was exhibited in Encore, Five Abstract Expressionists at Sidney Mishkin Gallery of Baruch College, The City University of New York in 2006.