In 1949 Georgia O'Keeffe honored the long friendship between Alfred Stieglitz and Duncan Phillips with a gift of nineteen photographs from Stieglitz's series of cloud photographs (1922-35). O'Keeffe accompanied the gift with the statement: "I know that I should send these to you because Stieglitz so often spoke of intending to send these himself. I think they will feel much at home with you." She thus gave recognition to the many years of association, respect, and friendship between Stieglitz and Phillips. Phillips greatly respected Stieglitz as an artist. He recognized his achievement in maintaining the realism of photography while addressing the goals of modernism, and he considered Stieglitz’s photographs of clouds important in joining photographic objectivity and personal emotion in his images. Phillips also sensed that he and Stieglitz were kindred spirits in their shared devotion to modern art, and Phillips felt that he, too, "had an ‘experiment station' as well as an intimate gallery where art can be at home."
Stieglitz photographed clouds from 1922 into the thirties. A symbolist aesthetic underlies these images, which became increasingly abstract equivalents of his own experiences, thoughts, and emotions. The theory of equivalence had been the subject of much discussion at Gallery 291 during the teens, and it was infused by Kandinsky's ideas, especially the belief that colors, shapes, and lines reflect the inner, often emotive "vibrations of the soul." In his cloud photographs, which he termed Equivalents, Stieglitz emphasized pure abstraction, adhering to the modern ideas of equivalence, holding that abstract forms, lines, and colors could represent corresponding inner states, emotions and ideas.