Lithol red salts: characterization and deterioration

Lithol Red salts are one of the commonest 20th century red synthetic organic pigments. We characterized the sodium, barium, and calcium Lithol Red salts with nuclear magnetic
resonance spectroscopy, powder X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, and laser desorption ionization mass spectrometry. The sodium and calcium salts were synthesized and compared to commercial samples. The single crystal structure of calcium Lithol Red is reported here for the first time. Light aging experiments show that the neat powder is very lightfast but that the pigment has poor light stability within paint systems. This suggests that the binding medium facilitates the photodegradation of the pigment for the latter case.