A technical examination of the nature and significance of prismatic lead white

Abstract

Prismatic lead white was first described by Walter C. McCrone in 1983 when it was identified via polarised light microscopy in three paintings by Edouard Manet. It is characterised by crystals in the shape of bullets or pills (i.e. prism-shaped, hence ‘prismatic lead white’). McCrone attributed the formation of these crystals, morphologically distinct from those of ‘normal’ lead white, to processing conditions characteristic of precipitated lead white. These ‘prismatic’ crystals have subsequently been identified as cerussite (orthorhombic lead carbonate, PbCO3). Their presence has been tentatively used to date artworks painted from the nineteenth century onwards. The article will show, through reproducing historic pigment recipes of post-treatments, that prismatic lead white can also be formed in the stack lead white process and so its presence should not be used as a criterion for dating. This article investigates the formation of these prismatic crystals in the context of the manufacture and history of lead white.