CuPc, a resolutely modern pigment

The advent of artistic modernity was accompanied by the appearance of new scientific techniques and numerous technological revolutions that completely changed the world of art. Industrialisation led to the wide-scale and low-cost commercialisation of a great variety of paints, whose so-called “synthetic” pigments were created in laboratories thanks to advances in organic chemistry.  With the appearance of ready-to-use tubes of paint, artists no longer made their colours themselves, as their predecessors did in the 16th and 17th centuries by crushing pigments and then mixing them with a binder such as egg yolk and later oil. 

Copper phthalocyanine blue (CuPc), belonging to the family of synthetic organic pigments, made its appearance on the market in 1935. Initially intended for the printing sector, the new blue rapidly entered other fields of application, especially in the coloration of plastics, paint for the automotive and building industries and artists’ paints. “As shown in the illustration in my thesis, nearly half of blue artists’ paints are based on phthalocyanine blue, alone or in combination with other pigments”, explains Catherine Defeyt. Its power as a colorant is superior to that of Prussian blue or ultramarine. It is much brighter than Prussian blue and less purple than ultramarine. Added to these qualities is its competitive price. According to the researcher, this particularly interesting price/quality ratio explains its intensive use in the manufacturing of blue oil paint. Copper phthalocyanine blue took the leading role, overtaking Prussian blue, ultramarine and cobalt blue.

CuPc inside out

Copper phthalocyanine blue is a polymorphous pigment that comes in five crystalline forms, created and patented by industry at various intervals in the 20th century. Conventionally known as alpha (α), beta (β), gamma (γ), delta (δ) and epsilon (ε) according to the Greek alphabet, the polymorphs of CuPc differ in stability, solubility and hue. However, only the alpha (α), beta (β) and epsilon (ε) forms were investigated by the scientist because these are the only three forms present in artists’ paints.