Zum Problem der Farbträger des Ultramarin-Grün und des Ultramarin-Rot / On the Problem of the Colored Species in Ultramarine Green and Ultramarine Red

ESR and UV/VIS spectra indicate that the color of ultramarine green is due to two radical ions S2 - (yellow) and S3 - (blue) whereas ultramarine red contains the neutral sulfur molecule S4 (red) predominantly. On heating in chlorine gas, ultramarine violet was converted to a red powder which exhibited the ESR signal of SO3 - with g = 2.0036 and in its reflection spectrum the characteristic band of S3 near 24,400 cm-1.