When Donald Judd very reluctantly abandoned painting in 1961-62 in favor of working in three dimensions, it was because he had finally concluded that a philosophically tenable painting was not possible – philosophically in the empirical-perceptual sense of being entirely available visually, and tenable in the sense of being free of abstraction or any other kind of representation. He called these 'illusionism' because they are all, in the strictest sense, contrary-to-fact, and therefore anti-visual.

Judd later objected on serious grounds to the term 'sculpture' for his work, but from 1962 until early 1964 (when he started having his work fabricated) this term was not entirely inappropriate, even on his own terms, in that these works, still noticeably handmade and hand-painted, remained, even though unintentionally, slightly expressive. As a former painter, Judd understood color and how it could be used — and, incidentally, considered all materials to be colored — but there was a lingering depictive, cosmetic, and surface-obscuring quality to applied paint.

In a 1963 floorpiece, Untitled (DSS 38), Judd covered what would otherwise have been a seventh broad area of hand-painted plywood, with a four and a half square foot piece of 1/8-inch opaque purple Plexiglas; the contrast of both colors and materials is defining. This piece, the earliest in the exhibition, is Judd's first use of Plexiglas. Later works include a 1989 (by now unpainted) plywood and brown Plexiglas wall-piece, Untitled (89-38 Ballantine), where the browns of the plywood and Plexiglas reinforce each other.

Plexiglas, manufactured (cast) between sheets of plate glass, takes on the consistent flatness, gloss, and material thickness of glass, but is much lighter and fairly easily worked with hand tools. Transparent Plexiglas—either colored or clear—has the optical clarity of glass. Opaque Plexiglas, unlike a layer of paint, has, as Judd said, the same saturated color "through and through" and an independent substantiality. This quality of Plexiglas being 'a better paint,' of being an improvement on applied paint, is only one of the paint-like ways Judd found to use colored Plexiglas. His previous use of straight-out-of-the-tube oil paint found a parallel in the strong, but limited variety of standard 'found' Plexiglas colors. Within ten years he was sometimes even using two layers of Plexiglas together, a transparent yellow, for example, over an opaque red, to achieve a third color — not orange, by the way — or, more rarely, colored transparent over paint, similar to something only possible in painting through glazes.

There are other ways Judd uses transparent Plexiglas that relate directly back to glass, especially stained glass, with its ability to seal, admit light, reveal and color interiors, as seen in a 1966 'single stack,' Untitled (DSS 89), and in a 1970 stainless steel and amber Plexiglas 'turnbuckle piece,' Untitled (DSS 234), where the entire interior and every detail of its dynamic construction is visually accessible.

Untitled, 1979 (79-40 Bernstein), an unusual variation on a classic transparent 'stack,' has red opaque Plexiglas top and bottom, referring back to both the glass and paint properties of colored Plexiglas.