FROM BECKMANN TO BASELITZ - TOWARDS AN IMPROVED MICRO-IDENTIFICATION OF ORGANIC PIGMENTS IN PAINTINGS OF 20 th CENTURY ART

Today, synthetic organic pigments play a major role as colorants of excellent light-fastness in artists' paints. Their analytical determination in paintings gains steady importance with respect to attribution and studio practice of certain artists as well as dating and authentication. Synthetic organic pigments have extremely varied chemical structures and properties such as colouring strength, solubility or thermal stability. Therefore, it is a challenging task to fully identify all organic as well as inorganic colorants and fillers in a micro-sample taken from a painting. A complementary sampling and analytical approach is suggested, that combines micro-chemical and solubility tests, Raman microscopy, pyrolysis gas chromatography/mass spectrometry, thin layer chromatography and/or high-performance liquid chromatography on a case-to-case basis. This paper presents results and discusses practical experiences with Raman microscopy as a rapid and minimally invasive technique for the identification of organic pigments in paint samples. Case studies from 20th century German artworks by Max Beckmann, Georg Baselitz, A.R. Penck and Markus Lupertz illustrate the potential and limitations of Raman microscopy and the need for complementary techniques, especially in the case of mixtures. Selected organic pigments, especially Pigment Green 7, Pigment Violet 23 or Pigment Yellow 83, are briefly discussed with respect to their use in artists' paints.