Like Sol LeWitt, Judd is interested in maximum impersonality in the facture (making) of his sculpture. His pieces are fabricated for him, this one by Bernstein Bros. a New York metalworking firm. Also like LeWitt he uses serial systems as a basis for his works, in order, he has said, to avoid traditional composition which, because it is imposed from outside the work 'dilutes the immediate experience'. 'Untitled' 1980, is one of a large group of similar works, often referred to as 'Stacks', made by Judd from 1965. Most consist of ten identical elements, although the materials used vary, and it is clear that Judd has a strong interest in the visual qualities of different materials. His combinations of coloured perspex with various metals have a visual beauty that in the generally austere context of Minimalism can look positively sensuous. His 'Untitled' 1977, also in the Tate Gallery collection, and made of polished copper, is another example of the material beauty of some of his work. The elements of Judd's 'stacks', however, are arranged with ruthless logic and impersonality, and in such a way as to relate organically, like LeWitt's wall drawings, to their environment. Thus, the work must as far as possible fill the whole space between floor and ceiling, while the space between the floor and the bottom unit and the space between each unit must be the height of one unit, in this case 230mm or 9 inches. The distance from the top unit to the ceiling must be not less than the height of one unit. In exceptionally high rooms the gap at the top maybe considerable, in low ceilinged rooms a unit or units may have to be omitted. The ideal arrangement would seem to be the use of all units and a gap at the top of more than one but less than two units. According to the art historian Irving Sandler, Judd began to use coloured perspex as an additional material because its colour was integral to the material and because it was transparent enough to be seen through, exposing the inner volumes of the boxes and eliminating mystery and ambiguity.
Simon Wilson, Tate Gallery: An Illustrated Companion, Tate Gallery, London, revised edition 1991, p.260