Color Stability of Early 20th Century Paints: A Comparative Study of Three Manufacturers

In this paper, we present the result of the study conducted on aging tests carried out by the artist Emile Claus (1849–1924), composed of oil paint samples from three manufacturers: Blockx, Lefranc Bourgeois and Fritz Behrendt. These colors were applied neat and mixed with white on wooden panels prepared with white ground layer. A non-invasive analytical protocol, combining imaging techniques and physico-chemical analyses, was used to characterize potential differences between manufacturers for nominally identical colors. The differences highlight in this study include variations in nickel content in cobalt blue colors and aluminum content in madder lakes. It also discusses the intrinsic and extrinsic factors that led to the degradation of certain colors. Hyperspectral imaging further demonstrated that the addition of lead white induces a systematic shift of spectral inflection points toward shorter wavelengths, consistent with the optical dilution effect in pigment-white mixtures, while the altered colors do not follow the same trend.