Non-destructive analysis of the optical effects of coloured grounds of paintings using flux-based statistical light scattering

A ground is a layer applied to a painter’s canvas or panel to create an evenly absorbing, monochrome surface. Coloured ground layers can have a crucial visual impact on paintings. Many seventeenth-century paintings have been executed on a coloured ground. This study introduces a Monte Carlo optical scattering four-flux model to explore how coloured ground layers affect the visual appearance of paintings. Utilising hyperspectral imaging and the developed optical model, we analysed two sets of paint samples to assess how variations in material composition, pigment size distribution, and linseed oil addition influence colour and transparency. The results demonstrate that the pigment size distribution influences the visual appearance and that smaller pigment particles enhance transparency, while adding glass powder or linseed oil further modifies the visual characteristics by increasing light transmission. Additionally, thickness differences resulting from uneven pressure of the brush affect average colour perception. These findings highlight the critical role of coloured ground layers and demonstrate the model’s effectiveness in the analysis of the transmission and reflection properties of coloured ground layers. This research enhances our understanding of optical effects in paintings and provides valuable insights into the painting technique and optical effects in historical artworks, particularly Netherlandish paintings from 1550 to 1650.