From the first third of the 15th century onwards, panel paintings with marbled reverses increasingly appeared in Flemish art. The fronts of these panels primarily depicted religious narrative scenes or portraits. The backs were decorated with an abstract pattern, referred to as marbling. These painted marble facsimiles often differed in terms of design from other examples of stone imitations such as those used on the frame decorations of other panels. Unlike these frames, which suggest a greater illusionistic intention, the marbled reverses appear to function as abstract ornamentation. However, this article proposes that the painted backs are thematically linked to the pictorial narratives of the fronts. The marbled backs of Rogier van der Weyden’s Crucifixion and the Portrait of Margareta van Eyck will be considered in the context of a profane and a theological iconography. Both panels feature a reverse that can be identified as both an imitation of red porphyry and a representation of liquid paint. Metaphysical, material–semantic, and theological references will be revealed in the pictorial examples.