In 1969, Donald Judd conceived of a number of rectangular floor works of anodized aluminum with open ends and lined with plexiglass on the inside; they were made in blue, violet, green, and dark brown. “The box with the plexiglass inside,” Judd said in 1971, “is an attempt to make a definite second surface.” He continued:

The inside is radically different from the outside. While the outside is definite and rigorous, the inside is indefinite. The interior appears to be larger than the exterior. The plastic is very slippery in look. There is one thing I know how to do well and that is to produce a plain, austere piece. It’s a quality that I like, and I get very skeptical about it. But I like to try other things to see what happens to the shape and surface. Also, I like to try different colors on the same form by using different materials.¹

¹ “Don Judd: An Interview with John Coplans,” in John Coplans, Don Judd, exh. cat. (Pasadena, CA: Pasadena Art Museum, 1971),44.