Investigation of 19th and early 20th century Prussian blue production methods and their influence on the pigment composition and properties

Several degradation phenomena, including cracking and paint loss have been observed in Prussian blue oil paint strokes in Vincent van Gogh's paintings. To understand the influence of the pigment on these phenomena, 19th and early 20th century preparation and purification methods of the Prussian blue pigment and their influence on its composition and properties were studied using contemporary sources. Recipes for replication were selected based on their prevalence, the detail in their description, as well as the quality ascribed to the prepared pigments. Two direct recipes, two indirect recipes, a conversion from soluble to insoluble Prussian blue and two 18th century recipes were used for the reproduction of Prussian blue, including the historical purification methods. The prepared pigments were analysed using ATR-FTIR, XRD and SEM-EDX. Differences between the pigments were found in the presence of certain contaminants, as well as in the size and shape of the pigment particles. These contaminants included nitrates and carbonates. The differences in particle characteristics were found to result in differences in shades and tinting strengths of the pigments and prepared oil paints.