In both wall painting and sculptural polychromy, paint serves to make form visible and intelligible by enhancing volumes, imitating materials (stone, metal, textiles, skin), and modulating light. On both supports, painting functions as a visual and illusionistic device, transforming raw material into image. Contrary to the widespread assumption that ancient wall painting relied primarily on buon fresco, archaeometric research has shown that dry stratification using organic binders—such as casein, wax, vegetable oils, and animal glues—was extremely common. In the middle and late Imperial periods, mixed techniques combining dry decoration with whitewash or very thin preparatory layers become predominant on walls and ceilings. Organic binders have also been identified in sculptural polychromy, pointing to shared materials, gestures, and application protocols. This technical convergence is particularly evident in pigment use, both in colour stratigraphy and in mixtures employed to deepen shadows, model reliefs, and enhance spatial depth. The systematic use of Egyptian blue provides a clear example: in both wall and sculptural painting it was mixed with other pigments to reinforce shadows, brighten the whites of the sclerae, and impart cooler, more naturalistic flesh tones. These parallels indicate that wall painting and sculptural polychromy formed part of a shared material culture of colour, based on common knowledge of pigment preparation, image construction, and the optical rendering of surfaces.
Tomassini et al. (Wed,) studied this question.