"...the floor paintings, which she worked on for about a decade, beginning in 1967. ... In 1971, Plimack Mangold introduced a new element, a full-length, wood-framed mirror, into her work. The mirror’s vertical shape suggests that it can be read as a surrogate for the viewer. In “Absent Image” (1972), the floor continues in the mirror, which reflects two rooms, the one in which it is situated and an adjacent room, which is..." http://hyperallergic.com/49598/why-there-are-great-artists-part-2/