Pigment Yellow G583‐a misclassified pigment and its relationship with other acetoacetanilide azo pigments

Pigment Yellow G583 (nominally C.I. Pigment Yellow 6) has been compared with another version of C.I. Pigment Yellow 6 (Recolite Fast Yellow 3G) and the colour and the X‐ray powder diffraction pattern have been found to be different. Density measurements, crystal structure analysis and chemical analysis have shown that the former is a mixed crystal of60 mol% C.I. Pigment Yellow 6 and 40 mol% C.I. Pigment Yellow 5. Pigment Yellow G583 was then compared crystallographically with a series of similar pigments, and it has been concluded that the structure of C.I. Pigment Yellow 6 is different to that of all the others. Regardless of composition, Pigment Yellow G583 is a mixed crystal of C.I. Pigment Yellow6 molecules in an α‐C.I. Pigment Yellow 5 lattice and not vice versa. This does not necessarily make Pigment Yellow G583 a poor pigment, but a change of composition may cause the crystal lattice to become that of C.I. Pigment Yellow 6, changing the physical properties. The only way in which a change of crystal structure can be detected is to examine the X‐ray diffraction pattern.