Painted in 1918, Portrait of Marcel Duchamp attests to the thorough transformation that Dreier's art underwent in the years following the Armory Show. Eschewing the traditional representational nature of her earlier work, Dreier renders her dear friend in an abstract, non-figurative manner. Rich yellows, blues, reds, and violets combine with triangles, circles, and other shapes to create a cacophonous composition. One searches the painting for some clues to Duchamp's identity, and perhaps one sees the letter D in the center and a pipe at center-left. Dreier, though, was not necessarily interested in these likenesses, instead she wanted to portray Duchamp's inner life. Of this painting, Dreier wrote, "[T]hrough the balances of curves, angles, and squares, through broken or straight lines, or harmoniously flowing ones, through color harmony or discord, through vibrant or subdued tones, cold or warm, there arises a representation of the character which suggests clearly the person in question, and brings more pleasure to those you understand, than would an ordinary portrait representing only the figure and face."
The work celebrates Duchamp, who, in Dreier's eyes, combined "originality of so high a grade" with "such a strength of character and spiritual sensitiveness," but its style owes much to another of Dreier's favored artists - the Russian abstractionist Wassily Kandinsky. While studying in Germany in 1912, Dreier read Kandinsky's On the Spiritual in Art and was inspired both by his view of "form as the outward expression of inner spiritual meaning" and by his synthesis of form and color. The two also shared an interest in the non-traditional, occult religion of Theosophy and the writings of Rudolph Steiner. The art historian Francis Naumann points out that in Kandinsky's treatise, the triangle suggests mystical enlightenment. The prominence of triangles in the composition suggest that Dreier saw him as an enlightened individual. She said of him, "I have always considered [Duchamp] one of the most advanced spirits of our Time," and Dreier once said, "and though I did not always understand what he was doing I was intuitive enough to let Time reveal it to me."
In the same year as completing the abstract portrait, Dreier commissioned Duchamp to produce a painting to hang above the bookshelves of her Manhattan apartment. The resulting work, Tu m', was to be Duchamp's last painting on canvas.
