A geometric abstract composition by František Kupka, featuring rhythmic black bands and layered green planes that explore spatial depth and visual movement.

František Kupka, a pioneer of abstract art, produced Diagonal Planes during a period of intense experimentation with geometric form and spatial perception. This work demonstrates his move away from representational subjects toward a language of pure structure. The composition relies on the interplay of rigid, dark vertical elements and a series of receding green planes, which create a sense of architectural depth without referencing specific physical objects. Kupka was deeply interested in the mechanics of vision and the way the human eye processes movement across a surface. In this painting, the sharp, white-outlined black bands act as conduits for the viewer's gaze, pulling the eye through the frame in a rhythmic, almost mechanical fashion. The use of a restricted green palette allows the focus to remain entirely on the geometry of the forms rather than on atmospheric effects or narrative content. The textured application of paint provides a tactile quality to the otherwise stark, mathematical arrangement of shapes. By the 1920s, Kupka had moved past his earlier, more fluid experiments with colour, adopting a more disciplined approach to composition. Diagonal Planes reflects this shift, showing a preference for clarity and order. The work functions as a study in spatial tension, where the overlapping planes suggest a three-dimensional environment that remains firmly anchored to the two-dimensional surface of the canvas. It is a precise example of how early twentieth-century abstraction sought to define a new reality through the arrangement of line, plane, and colour, independent of the external world.