The extraordinary nuances of a colour

 Written by Francesca Di Turo

Translated by Sarah Fortunée Tabbakh

Italian version here

“For me, each nuance of a colour is in some way an individual, a being who is from the same race as the base colour, but who definitely possesses a distinct character and soul.” (Yves Klein) 

One of the first topics that a student of applied science to cultural goods will cover is, most probably, the topic of the colour; and it is this topic we will address to launch our Blog. Much has been written and theorized about colour; a good example is Goethe (“The theory of colours”.) 

Walk into any bookshop and you will stumble upon books, both historical and contemporary, that address the topic… but why does colour spark so much interest? Many are the reasons, but, in my opinion, the main one is the difficulty in objectively quantifying a colour. In other words, colour is a subjective sensation, just like when one feels hot or cold. Our eyes contain unique structures that allow us to see the colour (for details, we invite you to read specialized essays) but its perception is, in any way, very personal. You might want to paint your house and ask for a “sky blue”, and get blue walls, and still ascertain that it is indeed a “sky blue”. 

 To solve this problem, science relied on colorimetry, that is, on all analysis that can objectively say “how much of a colour is a colour”. Most of the systems that solve this problem as old as time are based on the three additive primary colours: red, green and blue (RGB).

Source: rapidtables.com

Even when you draw on Paint, your computer is based on this system. Successively, two methodologies have been standardized for the systematic definition of the colour: the Munsell colour system and the CIE L*a*b colour space. Therefore, today, we can say with much precision which colour was used and when “red” is a red. Before the industrialization, the colours used were limited to a chart of pigments and natural or semi-natural colorants. The advent of chemical industry (when a certain young researcher that went by the name Perkins erred in synthetizing an antimalarial drug and created the first synthetic colorant, the mallow, therefore heading towards a happy chemical industry… talk about research!) the once several available colours became hundreds of thousands. 

The numbers increased so much and so fast that it became impossible to name them traditionally, like “Pompeian Red”, “Vermilion”, “Herculan Red” etc. A standardization of the nomenclature became necessary. We can all imagine how difficult it is to the naked eye to distinguish a #FF7F50 rgb(255,127,80) and a #FF6347 rgb (255,99,71). They are both orange, but different people will perceive them in a different way, and for some, there might not even be a difference at all. Colour is strongly linked to our psyche and its shades and nuances are also used to convince us to buy. Similarly, they can influence our state of mind, creating positive emotions (and interior designers know something about this). 

 If nowadays colour is still that important in art, in architecture, and simply in our daily lives, imagine how important it must have been in Michelangelo and Raphael’s times, for example. Let us try to think of a colourless artwork: impossible. Even better, it is possible but we would not like it as much. The colours of an artwork are often lost, they fade, they are altered, and the reasons are numerous and complex (storage location, exposure, thermal and hygrometric parameters, and these are but a few). To make a long story short, we perceive a colour because the radiation that reaches us is the one that has not been absorbed by the pigment, while the rest of the visible spectrum is absorbed by the particle. One of the major causes of the alteration of pigments and colorants is precisely their capacity to absorb the light, since they trigger photochemical reactions, which also depend on the substratum on which the pigment is found and the various interactions with the environment. 

That makes the light source of joy and pain for our pigment: without it, it could not be coloured, but at the same time, it is the cause of its alteration. Many are the artworks that have been subjected to chromatic variations and the conservation of the colour itself is problematic: Van Gogh’s sunflowers, Cimabue’s Crucifix in the Basilica of Saint Francis of Assisi or Michelangelo’s Last Judgment. 

Fortunately, on the latter, the chromatic variation, specially the blue of the sky, was not irremediable, but there had been heated discussions on whether or not to revive the colour through cleaning and how much cleaning had to be done. In conclusion, the nuances of the colours are infinite – there are not only fifty of them – and defining them with precision is challenging. 

However, this is exactly what makes this topic fascinating: we know for certain that we see colours because of a particular scientific mechanism, but their perception, their nuances, are subjected to each of us’ interpretation. 

 … Some essays to read on colour (that is, a reduced biography): 

• Philip Ball, Il Colore: Una Biografia • Rendiconti Accademia Nazionale delle Scienze detta dei XL, Memorie di Scienze Fisiche e Naturali 133° (2015), Vol. XXXIX, Parte II, Tomo I, pp. 147-160, La Diagnostica per la Conoscenza Storica e Artistica delle Opere d’Arte: il Ruolo delle Analisi sui Pigmenti nel Restauro degli Affreschi di Michelangelo nella Cappella Sistina, Francesca Di Turo, Franco Calascibetta, Giuliano Moretti, Gabriele Favero 

• Adriano Zecchina, Alchimie nell'arte • G. van der Snickt et al., Combined use of synchrotron radiation-based μ-XRF, μ-XRD, μ-XANES and μ-FTIR reveals to alternative degradation pathway of the pigment cadmium yellow (CdS) in a painting by Van Gogh, Analytical Chemistry 2012, DOI: 10.1021/ac3015627.