Exploring the colloidal structure of emulsion-based paints using nano-holotomography

The tempera grassa painting technique, based on emulsions of egg yolk and oil, is a key marker of the evolution of artistic practice during the Renaissance. Yet despite its significance in art history, it remains barely studied from a physico-chemical point of view. Distinctive properties may arise from the organization of the different phases (egg yolk, oil, pigment particles) at a colloidal scale. Therefore, a method allowing three-dimensional mapping and chemical identification of these systems at the nanometric scale is essential. We propose to carry out phase contrast X-ray nano-holotomography on laboratory-prepared paint samples for this purpose. Previous encouraging results were obtained on these samples and demonstrated the ability to discriminate egg yolk compounds from oil droplets thanks to the high spatial resolution allowed by synchrotron radiation and to the sensitivity of phase contrast tomography to organic compounds.