In 1926, when he acquired his first painting by Karl Knaths, Duncan Phillips regarded Knaths as a member of an esteemed group of modern artists in America whose individuality was not masked by adherence to abstraction. With the purchase of Geranium in Night Window (1922) in 1926, Phillips initiated patronage that would last until his death in 1966. He bought, traded, borrowed, and exhibited over the years, until he assembled the largest and most representative collection of works by Knaths.
Although he maintained connections with other artists and arts organizations through teaching and lecturing, Knaths worked independently and developed a highly original style. During the 1920s, modern European masters, as well as contemporary Americans, such as Kuniyoshi and Stuart Davis, influenced him. In his early work he explored the expressive use of color and space, as seen in paintings like Geranium in Night Window and Cock and Glove, 1927–1928.
During the 1930s Knaths developed a cubist style characterized by expressive line and the careful arrangement of color and plane—represented in the Collection unit by Harvest, ca. 1931–1932, and the late work Shacks, (1964). It was this signature style that Phillips had in mind when he praised Knaths's ability to create "humanizing abstraction" and "to keep the essence of life and the character of objects in [his] forms even when they go into the fascinating realm of creative design."
By 1942 Phillips felt that Knaths had absorbed the luminism of the "best French painting from Chardin and Cézanne to Bonnard and Braque," and had transformed it into a uniquely American idiom. The relationship between artist and collector lasted for more than thirty-five years. Their first contact was in the form of a letter from Phillips, who at first assumed the role of mentor but later came to consider Knaths as a friend and colleague. Phillips demonstrated his fervent belief in Knaths's abilities not only by his acquisitions, but also by numerous essays he wrote about his art. He considered him a unit artist by 1929 when he decided "to have a small room devoted to Knaths," and later that year he gave him his first one-person exhibition, which also provided the occasion for their first meeting. Phillips purchased works from the exhibition, and he wrote to Knaths: "[C]ongratulations on the sustained and distinguished beauty of practically all the pictures you sent me for our exhibition. They are light in touch and high in key." The friendship deepened in 1938, when Phillips asked Knaths to lecture at the Phillips Gallery Art School. Knaths returned regularly until 1950, and in the process, influenced many artists in the Washington area.