Shaped canvases are paintings that depart from the normal flat, rectangular configuration. Canvases may be shaped by altering their outline, while retaining their flatness. An ancient, traditional example is the tondo, a painting on a round panel or canvas: Raphael, as well as some other Renaissance painters, sometimes chose this format for madonna paintings. Alternatively, canvases may be altered by losing their flatness and assuming a three-dimensional surface. Or, they can do both. That is, they can assume shapes other than rectangles, and also have surface features that are three-dimensional. Arguably, changing the surface configuration of the painting transforms it into a sculpture. But shaped canvases are generally considered paintings.
Apart from any aesthetic considerations, there are technical matters, having to do with the very nature of canvas as a material, that tend to support the flat rectangle as the norm for paintings on canvas. (See Departing from the rectangular below.)
In the literature of art history and criticism, the term shaped canvas is particularly associated with certain works created mostly in New York after about 1960, during a period when a great variety and quantity of such works were produced. According to the commentary at a Rutgers University exhibition site, "... the first significant art historical attention paid to shaped canvases occurred in the 1960s...."
Pioneers of modern shaped-canvas painting
Abraham Joel Tobias made "shaped canvases" in the 1930s. Uruguayan artist Rhod Rothfuss began to experience with "marco irregular" paintings in 1942, late in 1944 publish in Arturo magazine your seminal text "El marco: un problema de la plástica actual"  Munich-born painter Rupprecht Geiger exhibited "shaped canvases" in 1948 in Paris, France. Paintings exhibited by the New Orleans born abstract painter Edward Clark shown at New York's Brata Gallery in 1957 have also been termed shaped canvas paintings.
Between the late 1950s through the mid-1960s Jasper Johns experimented with shaped and compartmentalized canvases, notably with his 'American Flag Painting' - one canvas placed on top of another, larger canvas. Robert Rauschenberg's experimental assemblages and "combines" of the 1950s also explored variations of divided and shaped canvas. Argentine artist Lucio Fontana also began early on the experiment in shaped and compartmentalized canvases with his Concetto Spaziale, Attese series in 1959. Assigning a date to the origin of the postwar shaped canvas painting may not be possible, but certainly it had emerged by the late 1950s.
Postwar modern art and the shaped canvas
Frances Colpitt ("The Shape of Painting in the 1960s"; Art Journal, Spring 1991) states flatly that "the shaped canvas was the dominant form of abstract painting in the 1960s". She writes that the shaped canvas, "although frequently described as a hybrid of painting and sculpture, grew out of the issues of abstract painting and was evidence of the desire of painters to move into real space by rejecting behind-the-frame illusionism." .
Frank Stella, Kenneth Noland, Charles Hinman, Ellsworth Kelly, Barnett Newman, Ronald Davis, Richard Tuttle, Leo Valledor, Neil Williams, John Levee, David Novros, Robert Mangold, Gary Stephan, Paul Mogenson, Clark Murray, and Al Loving are examples of artists associated with the use of the shaped canvas during the period beginning in the early 1960s. Geometric abstract artists, minimalists, and hard-edge painters may, for example, elect to use the edges of the image to define the shape of the painting rather than accepting the rectangular format. In fact, the use of the shaped canvas is primarily associated with paintings of the 1960s and 1970s that are coolly abstract, formalistic, geometrical, objective, rationalistic, clean-lined, brashly sharp-edged, or minimalist in character. There is a connection here with post-painterly abstraction, which reacts against the abstract expressionists' mysticism, hyper-subjectivity, and emphasis on making the act of painting itself dramatically visible - as well as their solemn acceptance of the flat rectangle as an almost ritual prerequisite for serious painting.
The apertured, superimposed, multiple canvases of Jane Frank in the 1960s and 1970s are a special case: while generally flat and rectangular, they are rendered sculptural by the presence of large, irregularly shaped holes in the forward canvas or canvases, through which one or more additional painted canvases can be seen. A student of Hans Hofmann, and sharing his concern for pictorial depth as well as his reverence for nature, she also favors colors, textures, and shapes that are complex, nuanced, and organic or earthen - giving her work a brooding or introspective quality that further sets it apart from that of many other shaped-canvas painters.
In the late 1960s, Trevor Bell, a leading member of the British St. Ives group introduced dynamic shaped-canvas paintings that combined radical, angular structures with an abstract expressionist sensibility. These works continued to evolve into the 1970s as Bell's works were exhibited in the Corcoran Gallery of Art in Washington, DC and The Tate Gallery in London. The artist’s highly chromatic, color field surfaces on massive canvases merged shaped painting and the subsequent blank space surrounding the object into a state of equal importance. The Italian artist Luigi Malice  also experimented with shaped canvases in the late 1960s.
Pop artists such as Tom Wesselmann, Jim Dine, and James Rosenquist also took up the shaped canvas medium. Robin Landa writes that "Wesselmann uses the shape of the container [by which Landa means the canvas] to express the organic quality of smoke" in his "smoker" paintings. According to Colpitt, however, the use of the shaped canvas by 1960s pop artists was considered at the time to be something other than shaped canvas painting properly speaking: "At the same time, not all reliefs qualified as shaped canvases, which, as an ideological pursuit in the sixties, tended to exclude Pop art." (op. cit., p. 52)
More recent shaped canvas art
Among shaped-canvas artists of more recent generations, Elizabeth Murray (1940–2007) produced playfully "exploding" canvases, in which exuberance of shape and color seems to force itself outside the normative rectangle - or, as a 1981 New York Times review put it: "...the inner shapes blast off from their moorings and cause the whole painting to fly apart." 
Singapore's Anthony Poon (1945–2006) continued the tradition of cool, abstract, minimalist geometry associated with the shaped canvas in the 1960s. The analytical poise and undulating repetitions in his work somewhat recall the work of modular constructivist sculptors such as Erwin Hauer and Norman Carlberg.
The globetrotting Filipina artist Pacita Abad (1946–2004) stuffed and stitched her painted canvases for a three-dimensional effect, combining this technique (which she called trapunto, after a kind of quilting technique) with free-wheeling mixed media effects, riotous color, and abstract patterning suggestive of festive homemade textiles, or of party trappings such as streamers, balloons, or confetti. The total effect is joyously extrovert and warm - quite opposed to both the minimalist and pop art versions of "cool".
In reference to the shaped paintings of Jack Reilly (born 1950), Robin Landa emphasizes the power of the shaped canvas to create a sensation of movement: "Many contemporary artists feel that the arena of painting can be greatly extended by the use of shaped canvases. Movement is established in the container (canvas) itself as well as in the internal space of the container." A 1981 review in Artweek stated "These intricately constructed pieces are related to wall sculpture, bridging the gap between painting and sculpture, they have an illusionary sculptural presence." An additional function of the shaped canvas in Reilly's earlier work was to emphasize the ambiguity of pictorial space in abstract art.
The Argentine artist Ladislao Pablo Győri (born 1963) became interested in non-representative and rigorous geometry formulations in the 1990s. The study of the paintings of the aforementioned Rhod Rothfuss led him to work in the realization of Madí Turning Paintings-Relief (irregular frame) and 3D digital animations of those geometric structures. Gyula Kosice (sculptor, poet, theorist, and one of the founders of the Argentine avant-garde of the 1940s) wrote: "He has rationally computerized the primordial ideas of Madi Art... I am convinced that his works radiate an undeniable quality and originality."
Departing from the rectangular
When thinking about shaped canvas it might be helpful to bear in mind that canvases are normally rectangular. Canvas is a woven material, with threads, called the warp and weft, lying at right angles to each other. In order to achieve equal tension on all the threads comprised by this fabric, stretcher bars, usually of wood, form a frame that mimics the layout of the threads of the fabric. There is therefore an inherent reason for paintings to be flat and rectangular – although artists have often departed from the norm, especially in circumstances requiring special commissions, an example being the paintings Henri Matisse created for Albert C. Barnes and for Nelson Rockefeller.
Dust tends to gather on the surfaces of any three-dimensional object. Keeping a complicated shaped canvas painting clean can require care and attention that can be avoided by sticking to flat-surfaced paintings.
In certain instances shaped canvas paintings can be seen as painting in relationship to sculpture and to wall relief. During the early to mid-1960s many young painters born in the 1920s, 1930s and 1940s made the transition from painting flat rectangles to painting shaped canvases; some of those artists decided to make sculpture and some artists like Kenneth Noland, Frank Stella, and Ellsworth Kelly did both. Other materials can be used in place of canvas. More viable materials might obviate some of the drawbacks of shaped canvas.
- Arthistory.about.com page on Raphael's "de Brécy" tondo canvas painting
- Image of a 1935 Abraham Joel Tobias shaped-canvas painting at the Zimmerli Art Museum (Rutgers University)
- Wechsler, Jeffrey; Abraham Joel Tobias; Jane Voorhees Zimmerli Art Museum.; Queens Museum. Abraham Joel Tobias : sculptural paintings of the 1930s (New Brunswick, N.J. : The Museum, 1987) OCLC 18137181
- Colección Cisneros "Arlequin 1944"
- Lenbachhaus - Rupprecht Geiger zum 100. Geburtstag Lenbachhaus - Rupprecht Geiger zum 100. Geburtstag
- The History Makers - Ed Clark Biography
- Metro Times Book review of Edward Clark: For the Sake of the Search in the Detroit Metro Times, stating that Clark is "widely credited with making the first extended shape painting (continuing the painting out of its rectangular frame with paper and wood) in 1956. "It wasn't called a shape painting then, just something strange and different that began with that painting," Clark said. The untitled work was shown in 1957 at the Brata Gallery..."
- The Shape of Paintings in the 1960s Retrieved June 23, 2010
- Barbera, Lucio. Luigi Malice: Percorsi della memoria 1959-1999, Roma: Gangemi Editore, 1999 ISBN 88-7448-906-4 
- Landa, Robin. An Introduction to Design, Inglewood: Prentis Hall, 1983 ISBN 0-13-480624-7
- NY Times review: "ART: EXPLODING CANVASES OF ELIZABETH MURRAY", May 8, 1981.
- Jaconson, Linda. Two Dimensional Reliefs, Artweek, Vol.12, Nov 21, 1981
- lpgyori.net page on Győri's digital works - art + poetry _ 1984/2003 > Madí Paintings-Relief
- Győri, Ladislao Pablo. First 25 Visual Years, ARTgentina, 2010, p. 29, ISBN 978-987-05-8040-9
- Barnes mural. Accessed August 7, 2007
- Clark, Edward; Barbara Cavaliere; George R N'Namdi. Edward Clark : for the sake of the search (Belleville Lake, Mich. : Belleville Lake Press, 1997) OCLC: 40283595
- Colpitt, Frances. [article] "The Shape of Painting in the 1960s". Art Journal, Vol. 50, No. 1, Constructed Painting (Spring, 1991), pp. 52–56
- O'Connor, Francis V. Jackson Pollock exhibition catalogue (New York, Museum of Modern Art, 1967) OCLC 165852
- Solomon R. Guggenheim Museum, The Shaped Canvas : December 1964 (New York : The Museum, 1964) OCLC 6244601 exhibition catalogue and commentary
- Stanton, Phoebe B., The Sculptural Landscape of Jane Frank (A.S. Barnes: South Brunswick, New Jersey, and New York, 1968) ISBN 1-125-32317-5
- John Weber; California State College, Los Angeles. Fine Arts Gallery. New sculpture and shaped canvas : exhibition (Los Angeles : California State College at Los Angeles, Fine Arts Gallery, 1967) OCLC 24634487 (Worldcat link: )