This painting was first exhibited at Documenta IV in Kassel in 1968, where it was entitled simply Untitled (diptych) and dated 1967. In 1974, just after the Australian National Gallery bought the picture, the artist changed the title to Untitled (vertical flanking diptych — red), and the date to 1966-74, thus identifying the painting with a series of works. The basic format of this series was well established in Baer's work by 1966. Each painting, or panel if the work was composite, was articulated by three colours: an expansive white central area (from 1967 grey was also used), a black band of uniform thickness placed at the outer edge of the canvas, and a thin line of colour either stripped in between the black border and the lighter centre as in the Gallery's work, or running through the black band. Also in 1966 Baer began to make diptych and triptych groupings of this format, arranging the diptychs in various configurations: laid horizontally and 'stacked' on the wall one above the other, or hung vertically flanking each other.
This serial experimentation within a limited format was typical of Minimalist painting during the 1960s and Baer was a vocal advocate of such painting. The September 1967 issue of Artforum carried a letter from Baer defending painting against the criticism levelled by Robert Morris (b. 1931) and Donald Judd (b. 1928), at what they regarded as painting's inherent and incorrigible illusionism. In reply Baer asserted the primacy of painting as a radical art form, arguing that its qualities of objectness' could be as non-referential and specific on a flat plane as 'objects' made in three dimensions.1 Nevertheless, in a number of paintings made towards the end of 1967 and in 1968 Baer felt the need to accentuate the object status of her paintings and began to thicken her stretchers and continue the painted surface around the sides. This is the moment of the Gallery's painting, the sides of which are 7.4 cm (27/8".) thick and painted white, running around onto the front surface of the canvas in a thin white line.
Michael Lloyd & Michael Desmond European and American Paintings and Sculptures 1870-1970 in the Australian National Gallery 1992 p.378.