on upper member of stretcher reverse: G. O Keeffe; on lower member of stretcher reverse: 1928; on right side of stretcher reverse: #21; by Alfred Stieglitz, except for "Coiled", across center reverse: 1928 / Georgia O'Keeffe (Coiled) / Shell No. 1 / Exhibition 1929; possibly by Alfred Stieglitz, across center reverse, within five-pointed star: OK; across center reverse: #21 / 1928.
The artist; sold 1953 through (Downtown Gallery, New York) to private collection, New York; the artist [1887-1996], by unknown date; her estate; bequest 1987 to NGA.
- Georgia O'Keeffe: Paintings, 1928, The Intimate Gallery, New York, 1929, unnumbered.
- Wilmerding, John. American Masterpieces from the National Gallery of Art. Rev. ed. National Gallery of Art, Washington, D.C., 1988: 176, repro.
- American Paintings: An Illustrated Catalogue. National Gallery of Art, Washington, 1992: 250, repro.
- Lynes, Barbara Buhler. Georgia O'Keeffe: Catalogue Raisonné. 2 vols. New Haven and London, 1999: 1:366, no. 622, color repro.
- Kirsh, Andrea, and Rustin S. Levenson. Seeing Through Paintings: Physical Examination in Art Historical Studies. Materials and Meaning in the Fine Arts 1. New Haven, 2000: 264.