Chromatic analysis of Roman frescoes in a Pompeiian domus

Colours perception depends on many factors, some attributable to sources used to light the observed objects and others to the optical properties of the objects themselves and of the space they are located in. Moreover, it cannot be neglected that, as for all visual phenomena, colour perception is also influenced by observer’s psychological and physiological conditions. Although the enhancement of colours perception is central in all lighting designs, it obviously becomes crucial in cultural heritage applications. In these cases, it is fundamental to define a proper balance between the necessity to highlight chromatic coordinates of lit artworks and to protect them by the light-connected damages, fulfilling prescriptions about maximum exposure levels [1]. The complexity of lighting design is greater when artworks are not located in museums or exhibition rooms, but are positioned in their original place and the entire architectural space must be considered a piece of art, e.g. churches or archaeological ruins. In these cases, design problems are greater: the location of luminaires is difficult because their installation must not adulterate the integrity of the cultural good; moreover, often it is not possible to access to all architectural spaces and consequently it must be considered that the artwork to lit (e.g. a fresco or a mosaic) will be observed from a specific distance and that its details will not be entirely appreciated by the observers. In order to account all these aspects, when lighting design deals with cultural heritage the preliminary analyses are crucial. Given these premises, the goal of this paper is to present a methodology useful to scientifically characterize artworks colours and to provide a valuable tool to choose the most suitable electric artificial sources in order to highlight their chromatic properties. This methodology was used during the preliminary studies to define the lighting system for some of the most famous ancient roman frescoes: the frescoes of the triclinium of the villa of the Mysteries in Pompeii. Specifically, the analysis focused on the wall in front of the entrance of the triclinium. It was divided in two parts: the analysis of the current lighting conditions and the chromatic analysis of fresco colours. Daylight irradiance measurements and luminance maps were obtained to characterize the luminous environment. Then dynamic daylight simulations were performed to identify the recurring daylighting conditions inside the triclinium. The fresco was divided in several chromatic areas based on its predominant colours. Each area was characterized by means of spectral reflectance factors measurements and the chromatic coordinates of the measured samples were identified and compared.