Phthalocyanine and quinacridone pigments: their history, properties and use

Abstract

It is the aim of this review to describe and characterize two groups of synthetic organic pigments, the phthalocyanines and quinacridones, which resemble each other in terms of their symmetrical structures, extensive conjugated networks and physical properties. They are very stable to light, heat, acid, alkali and solvents – properties considered desirable in pigments. These two classes of pigments, which first appeared commercially in the 1930s (phthalocyanines) and 1950s (quinacridones), are used extensively in the paint industry, in printing inks and for the coloration of plastics and textiles. Copper phthalocyanines are presently the primary blue and green paints used in artists' materials. While less prevalent than the phthalocyanines, the quinacridones are often used in artists' and industrial paints. These pigments can be characterized by analytical techniques such as X-ray diffraction, Raman spectroscopy, ultraviolet/visible spectroscopy and various pyrolysis techniques, although identification can be difficult since they can be present in very small quantities. Because these pigments are used in many artists' materials and have been since their introduction as colorants, their history, properties and methods of analysis are of interest to the field of conservation.