Petra Šulcová

Cerulean blue is a pigment that was introduced to the art market at the turn of the 1850s and 1860s, with its composition stated as CoSnO ₃ . For this project, the pigment was synthesised using historical recipes and analysed. The investigation involved examining various conditions for its preparation, such as different reactants, solution concentrations, precipitate ageing times, firing temperatures and calcination times. All of the samples obtained were green in colour, and their composition was defined as a mixture of SnO ₂ and Co ₂ SnO ₄ . To gain a more accurate understanding of pigment composition, historical paint samples and commercially available pigments were analysed. These pigments were found to contain a relatively high amount of magnesium, so new pigment samples were prepared with added magnesium. The obtained samples have the desired blue colour; their composition is Mg _2‐x Co _x SnO ₄ and SnO ₂ . Using K ₂ SnO ₃ ·3H ₂ O as a reactant produced more reproducible results than using SnCl ₄ ·5H ₂ O. The reconstruction of pigment production methods revealed gaps in historical recipes. The collected data allowed us to specify the composition of cerulean blue pigment as Mg _2‐x Co _x SnO ₄ with a variable amount of SnO ₂ .

This paper deals with the use of high-performance liquid chromatography in the identification of red synthetic pigments on samples from artworks. These pigments have usually low solubility, so it is necessary to choose a suitable extraction method for their conversion to the liquid phase, the optimization of which is the main focus of this paper. Various extraction methods have been tested and compared on a wide range of synthetic pigments. Oxalic acid extraction proved to be the most suitable extraction method, which was subsequently successfully verified on samples taken from artwork.