Synthetic organic pigments of the 20th and 21st century relevant to artist's paints: Raman spectra reference collection.

Some 170 organic pigments relevant to artist's paints have been collected from historic collections and modern manufacturers. The number includes multiples of the same pigment from different sources and comprises 118 different color indices (C.I.). All of them have been analysed with FTIR spectroscopy and 125 pigments (93 different C.I. No.s) of particular relevance to artist's paints have been characterised with Raman spectroscopy so far. The pigment collection encompasses the following pigment classes and subgroups: monoazo pigments represented by acetoacetic arylide yellow (hansa yellow), beta-naphthol, BON, naphthol AS and benzimidazolone; disazo pigments with disazo condensation, diarylide, bisacetoacetarylide, pyrazolone; azo-azomethin metal complex pigments; non-azo, polycyclic pigments such as phthalocyanines, diketopyrrolo-pyrroles (DPP), perylenes and perinones, quinacridones, isoindolinones, polycarbocyclic anthraquinones and dioxanines. The selection of references was based on availability (historic collections) and current use in 16 acrylic, alkyd and oil-based artist's paints, and it covers pigment colors PY yellow (27 C.I. No.s), PR red (38), PO orange (9), PB blue (8), PV violet (6), PG green (3) and PBr brown (2). Besides peak tables and spectra patterns, flow charts based on color, pigment class, group and individual color index are presented to help identification of unknowns and mixed paint samples. While Raman could isolate all different C.I. numbers, multiple references of the same C.I. from different sources could not be distinguished.