Reliefs are indicative of Mack’s entire oeuvre and play a central role in his artistic practice from very early on. Mack used reliefs as intermediaries between two-dimensional and three dimensional artworks. When he founded the Zero Group with Otto Piene, the artist declared that the 50s abstractions “had painted the whole world, beside sky, air and light”. The relief allowed him to integrate these elements in his artistic practice, acting as light catchers while at the same time possessing painterly qualities and shapes. In fact, as light and natural landscape became more central into Mack’s work, the artist sensed that the means of painting were no longer sufficient to display his new artistic reality. In 1959, Mack started drafting his Sahara Project, and in 1961 he published in “ZERO 3”, further details of this project of immense spatial dimension, through which he was willing to create a “reservation of art in natural spaces”. The incomparable light of the desert could outshine the works’ materiality completely, while the sand stretched out below it as the ultimate natural relief. In Sand Relief, 1968, we can see a continuation of Mack’s interest in the use of sand in his work, albeit on a much smaller scale. But as Mack’s monumental desert-based works were fleeting and could only be captured on film, in Sand Relief, the combination of resin and sand captures the markings that have been etched into the surface.