One is familiar with Martinmüller's uncompromising system of combining rectangular forms, which follows a principle comparable to music. The square basic element in connection with its color characterization determines the coherence of the motif units. Martinmüller chooses the rectangle as a measurable, absolutely joinable building block of his creations. These elements can be led in thought-out construction to complex orders. The assemblies are developed in lengthy studies and experiments. The realm of sounds, leading tones, intermediate tones that emerge in the end is comprehensible, but ultimately eludes any analytical precision. This is even more evident in the experimental early work. In a series of small-format paintings from 1970, the emotional approach even predominates. Here, however, we can already see a striving to put the mathematically based information-theoretical aesthetics of Max Bense into the picture - Martinmüller had, after all, studied with the "house philosopher" of Concrete Art. Inspired by the color field painting of Mark Rothko - who possibly attracted the young artist's attention even more through his death in 1970 - Martinmüller created color space miniatures that only became accessible in the dialogue between viewer and work. In these postcard-sized acrylic paintings on black cardboard, he explored the play of multiple colors, usually muted by overpainting. The brushstrokes enliven the surface, fray nervously at the edges of the color field, and yet find a balance in the overall sound that unfolds a poignant pathos in the softly melancholy color world that Sean Scully, for example, later discovered for himself on a grand scale.