Rheology of white paints: How Van Gogh achieved his famous impasto

摘要

Paints based on white pigments are the basic materials found in ground layers of ready-made canvases as well as in painting layers mixed with other colours. It is surprising that Vincent Van Gogh, whose unique style is world famous, resorted to not one but two types of white paints. Indeed, Van Gogh often used both lead white and zinc white in the very same painting, contrasting then with the majority of his contemporaries who have only used the traditional lead white. To trace the evolution of his painting technique and to respond to the issues of authentication, dating and preservation raised by his artwork, it is essential to have a good knowledge of the painting materials he used and how he used them. This paper describes the reconstructions of 19th century white paint formulations and their rheological characterization in order to compare their flow properties: by adjusting them, different paint finishes from smooth surfaces to high impastos can be produced. We define a general procedure for paint rheology characterization, useful for old recipes reconstructions in the field of conservation science. Both lead white and zinc white based paints exhibit a similar rheological behaviour, with a fluid to solid transition, and variations of their properties such as yield stress and elastic moduli, depending on their formulation (oil nature, content, and treatment). An explanation on the specific use of zinc white can be proposed as it allows higher impastos than a lead white paint containing the same oil content.