Variations in the colorimetric characteristics of verdigris pictorial films depending on the process used to produce the pigment and the type of binding agent used in applying it

The term verdigris embraces a wide range of synthetic pigments whose compositions can also vary. All are salts of copper, but their chemical composition will vary depending on the ingredients used to synthesize them and the conditions in which that synthesis is performed. This article presents the results of applying some of the recipes contained in treatises; the recipes used here, specifically, were taken from the Mappae Clavicula (12th century) and the Ms. of Pierre Lebrun (17th century). The ingredients mentioned present some variations, so that the pigments prepared in turn exhibit significant differences in terms of chemical composition and colorimetric characteristics. The recipes from the Mappae Clavicula, for example, produced monohydrated copper(II) acetate, which upon binding with gum arabic created bluish‐green pictorial films, whereas the colour was yellowish green when the binder was linseed oil. The pigment made from Pierre Lebrun's recipe was a copper(II) chloride mixed with an organo‐copper complex, which can be bound with gum arabic to produce a yellowish‐green colour, whereas mixing with linseed oil presented certain difficulties. These results are derived from colorimetric measurements, which were used to produce values of lightness (L), chroma (C) and hue (H), and also percent reflectance spectra.