25 planes is the fourth of a series of approximately eleven closely related sculptures fabricated in stainless steel and characteristically made up of rectangular planes arranged in two dimensions. In the special edition of Arts devoted to David Smith, published in February 1960, the artist stated that he 'started in 1957 with a series of stainless steel pieces from nine to fifteen feet tall. They are conceived for bright light, preferably for the sun, to develop the illusion of surface and depth. Eight works are finished.'1 In 1962 Smith further described this group: 'I'm still working on the stainless steel pieces. These I call Unities, and they are further identified by the number of planes they have. I have no tangible word relationships with subject matter where these are concerned. They're completely visual.'2
It seems likely that Smith's adoption of stainless steel as a medium in 1957 determined the basic characteristics of this group. As the stainless steel was much harder to cut than the metal he had used previously, Smith ordered pre-cut plates in an assortment of basic geometric shapes from Ryerson Steel Fabricators, his suppliers. This restriction provided the simple repertoire of squares and rectangles used in the 'Unities'. Cautious with the new material, Smith would lay out the elements on a flat surface to determine the final arrangement, then join them with the welder in this basically two-dimensional array. The arc welder used to join the metal left a deposit that had to be ground away, a fact that may have encouraged Smith to make a feature of the circular scouring of the surface of the planes.3 Work on the 'Unitites' ceased when Smith began work on the 'Voltri' series in June 1962.
Michael Lloyd & Michael Desmond European and American Paintings and Sculptures 1870-1970 in the Australian National Gallery 1992 p.295.