Shades of cyan

Cyan is the oldest and most abundant organic colour to have existed on Earth, and yet the most elusive of primary colours for human artistry1. As a dye or as a pigment, cyan is one of the subtractive primaries, which combines with yellow and magenta to produce a full palette of reflected hues for fabrics and paints2. No natural dye or pigment has the perfect cyan quality of absorbing all red light, to reflect only blue and green. Until the first synthesis of mauvine dye in 1856 and phthalocyanine pigment in 1927, and their subsequent derivatives, fabrics and paints approximated the reflected-colour wheel with mixes of naturally-sourced blue, yellow and red colourants3. That natural chromatic palette leaned heavily towards warm colours and earth tones. Greens were muted or olive, not bright and vibrant, and blues could neither extend into brilliant violets, nor emulate the vivid cyan of tropical waters or gemstone turquoise. The completion of the subtractive-colour wheel – by chemists using products of the Industrial Revolution – coincided with a revolutionary shift in Western pictorial art beginning c. 1860, towards impressions of light, saturated colours and expressive styles4.

• The earliest photosynthesising bacteria evolved into the most abundant lifeform ever to have existed on Earth: the cyanobacteria. Their cyan appearance comes from a blend of phycocyanin light-blue pigment with chlorophyll green pigment. Phycocyanin is sensitive to light, temperature and pH, rendering it unsuitable for human uses as a colourant.
• Unlike cyan, magenta is absent from the visible spectrum of light, making it an extra-spectral colour. The human brain perceives magenta through stimulation only of S- and L-cone cells, sensitive to short-wave blue and long-wave red light, and not of the M-cones for middle-wave green light. Its hue is the seam in a colour wheel formed by joining the two ends of the linear spectrum of visible light that extends from the shortest wavelength of blue to the longest wavelength of red. Like cyan, magenta is common in nature. Being the complementary colour of green, it affords flower petals their highest contrast with green foliage, and thus the highest visibility to their pollinators. As with natural cyan pigments, the magenta pigment anthocyanin in plant petals is too chemically unstable for human uses in paints. But a natural carmine dye with magenta shades has been used in Mesoamerica since at least the 2ⁿᵈ century BCE, made from dried and crushed cochineal, a scale insect parasitic on cactus.
• Mauvine was the first of the analine dyes, inspiring the synthesis of fuchsine dye in 1859, subsequently renamed as magenta, and phthalocyanine blue pigment in 1927, leading finally to monastral blue pigment in 1935, a pure cyan colourant.
• Modern art in Western culture encompasses the c. 100-year period 1860-1960.

C.P. Doncaster, Timeline of the Human Condition, star index