Painting cracks: A way to investigate the pictorial matter

An old painting generally exhibits a wide variety of crack patterns. From a strictly aesthetic point of view, cracks are undesirable; nevertheless, they can be seen as the fingerprints of the painting and provide valuable knowledge about the art piece. Precisely, the morphology of crack patterns can be related to the mechanical properties of the pictorial matter or they can reveal information about the methods used by the artist or the conditions of conservation. In the present paper, we show how drying dispersions of colloidal particles in a volatile solvent on a non-porous substrate provides a good candidate to study crack formation in a solid layer. We recover the crack patterns observed in paintings, and we investigate the role of the substrate, e.g., the sub-layer, and of the thickness of the layer in the crack spacing. We show how to deduce mechanical properties of a sub-layer, provided the thickness and the elastic modulus of the layer are known. These experiments aim to propose a potentially non-invasive method to deduce quantitative information about mechanical properties of a pictorial matter which could be of great interest for cultural heritage.