How nature produces blue colors

Abstract

Today, blue is a very fashionable color in European countries. This has not always been the case (Pastoureau, 2000), as cultural perceptions have slowly evolved since prehistoric times. In cave paintings, white, red and black have been the only available tones and these colors remained basic for Greek and Latin cultures, where blue was neglected or even strongly devalued. The word caeruleus, which is often used for brightly blue species, in naming plants and insects, is etymologically related to the word cera, which designates wax (not to the world caelum – sky – as often believed): it meant first white, brown or yellow (Andre, 1949), before being applied to green and black, and much lately, to a range of blues. Latin and Greek philosophers were so diverted from blue that they even did not notice its presence in the rainbow: for Anaximenes (585-528 BC) and later for Lucretius (98-55 BC), the rainbow only displayed red, yellow and violet; Aristotle (384-322 BC) and Epicurus (341-270 BC) described it as red, yellow, green and violet. Seneca (ca. 4 BC 65 AD) only mentioned red, orange, green, violet but, strangely, also added purple, a metameric color not found in the decomposition of white light. Later in the Middle-Ages, Robert Grosseteste (ca. 1175-1253) revisited the rainbow phenomenon in its book “De Iride” and still did not find there any blue color (Boyer, 1954). Blue emerged slowly in minds and art, only after the advent of technological breakthroughs in stained glass fabrication (as introduced in the 12th century rebuild of St Denis Basilica) and after the progressive use of blue dyes, which followed the extension of woad cultivation, all after the 13th century.