Analytical studies on commercial artists’ colour charts from Das Deutsche Farbenbuch (1925)—identification of synthetic and natural organic colourants by Raman microscopy, surface-enhanced Raman spectroscopy and metal underlayer ATR-FTIR spectroscopy

Abstract Historical colour charts provide a rich and often well-dated reference materials source for studying the chemical composition of all kinds commercial brands artists’ paints. This article presents results an extensive analytical study more than 80 paint hues from 11 that are included in German standard book Das Deutsche Farbenbuch by H. Trillich (1925, Part II). Our research focused on identification synthetic organic pigments, whose quickly increasing significance paints early twentieth century is impossible to evaluate documentary alone. A stepwise procedure combining different non- or minimally invasive vibrational spectroscopy techniques—Normal Raman Surface-Enhanced as well Metal Underlayer Attenuated Total Reflection Fourier-transform Infrared Spectroscopy—allowed 18 colourants watercolours, tempera oil colours six manufacturers. In addition, micro-X-Ray Fluorescence was applied determine elemental pattern substrates, fillers, admixed inorganic pigments. addition few traditional natural (dark rose madder lake, cochineal lake), most identified compounds comprised pigments dyes various classes (indigo, anthraquinone, monoazo, ß-naphthol, xanthene, triarylcarbonium, nitroso, azine compounds). Some these have not only rarely been reported so far. Since mainly poor fair (only sometimes good) fastness light according modern standards partially also solvents typically used conservation treatments, it evident works art this period should be treated keeping mind possible presence such colourants, when planning both interventive treatments preventive measures.