In the NICAS I3GlassP seed-money-project, optical coherence tomography (OCT) was employed to visualize the subsurface morphology of colourless-glass-in-paint layers in reconstructions. Using custom-developed software, we expanded the analysis from mere visualization to quantification of size, distributions and refractive indices. The imaging- and analysis-pipeline is now applicable to paints, containing glass-based pigments such as smalt in case studies from the Rijksmuseum collection.
In this NICAS-SPG project we will take the next step and investigate the influence of morphology on colour and extend our study to the behaviour and colour of smalt, a glass-based pigment, in an oil matrix. We propose a combination of quantitative measurement, using OCT and Low-Coherence Spectroscopy (LCS), and light-transport modelling to reveal the underlying phenomena which are responsible for the visual appearance of glass-based paints. This plays a crucial role in understanding the optical effects of added colourless glass to paint as well as the influence of morphology and degradation of smalt on its appearance, such as colour, hue and saturation.
When validated, our approach is applicable to other semi-transparent materials containing layers and inclusions, both in cultural heritage as well as biomedical research.