For Heinz Mack grids are not a means to mark a borderline in the sens of a fence, instead they are filters for the light that make variations from light to dark visible. This work clearly illustrates this approach: the work has everything from subtle shades of light gray all the way to a dense surface; created from a powdery spray application on a grid fan. In his dedication on the sheet Heinz Mack references one of his most famous projects, the "Sahara-Projekt", which he conceived in 1958 and partly realized in 1968/69: "it is no coincidence that a Fata Morgana appears in the desert".