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.

油调蛋彩画法（tempera grassa）是以蛋黄与油的乳浊液为基底的绘画技法，是文艺复兴时期艺术实践演变历程的关键标识。尽管该技法在艺术史中具有重要意义，但从物理化学视角对其开展的研究仍寥寥无几。这类体系的独特物化特性，或许源于胶体尺度下不同组分相（蛋黄、油滴、颜料颗粒）的微观组织排布。因此，开发一种可在纳米尺度下对该类体系实现三维测绘与化学识别的方法至关重要。为此，我们提出采用相衬X射线纳米层析成像技术（phase contrast X-ray nano-holotomography）对实验室制备的绘画颜料样本开展相关研究。此前我们在这类样本上已取得令人鼓舞的实验结果：得益于同步辐射光源提供的超高空间分辨率，以及相衬层析成像技术对有机化合物的出色检测灵敏度，该方法已能够有效区分蛋黄组分与油滴。