The following are excerpts from an interview between John Coplans and Donald Judd on the occasion of the exhibition Don Judd at the Pasadena Art Museum in 1971.
John Coplans: Why the use of Plexiglas?
Donald Judd: It has a hard, single surface and the color is imbedded in the material. In some cases it also gives access to the interior-- to a varying degree, however.
John Coplans: With the wall pieces I imagine the use of the Plexiglas is important because the observer can see through the piece.
Donald Judd: The use of Plexiglas exposes the interior, so the volume is opened up. In the large piece owned by Pasadena the viewer has a clear idea of the volume because he knows how thick the walls are even though it can't be seen into. It's fairly logical to open it up so the interior can be viewed. It makes it less mysterious, less ambigious. I'm also interested in what might be called blank areas, or just plain areas, and what is seen obliquely, so the color and the plane and the face are somewhat obscure compared to the front. It's the other way around when seeing the side. In most of my pieces there are no front or sides-- it depends on the viewing position of the observer.
John Coplans: I understand the stacks exist in the following variations: galvanized iron, copper, and stainless steel, and there soon will be one of brass. Then there are the various stacks of different colored Plexiglas with each type of metal.
Donald Judd: Yes, first you have the solids, the Plexiglas top and bottom, and finally the wraparound Plexiglas sides.
John Coplans: Do you work in editions in the stacks? Are there more than one of some combinations of material?
Donald Judd: No, they are all unique. Again, it's a question of money. If I had more money, a lot of possibilites would have gotten done at one shot. That's somewhat true of the stacks. The ones of galvanized iron were made first because they were the cheapest to make. On the other hand, it's five years or more since I made the first stacks, and in that time many more ideas have occurred, so I probably couldn't have made them all at once. So there is the development in the materials to allow for a wider range of plastic in different colors-- some transparent, translucent or opaque. I didn't think, at first, of opening them from top to bottom. That only came later. And I didn't think of the wraparound until after that.
(J. Coplans, Don Judd, Pasadena 1971, pp.36-37).