Chevreul’s simultaneous contrast

Knitters know that the dyeing of yarn is important. We seek out the shades we love from the indie dyers we admire, we take classes to better understand the behaviour of natural dyestuffs, we obsess over particular sell-out hand-dyed colourways. We all love dyed yarn. But did you know that the process of yarn dyeing was responsible for one the most influential ideas about colour to have emerged over the past two hundred years? Let’s wind the clock back to 1830s Paris, where the managers of the prestigious state-owned Gobelin Tapestry works had concerns about colour matching and colour fastness in the organically-dyed yarns they used. Why, they wondered, did black yarns produced from the same fibres to exactly the same dye recipes look so different from one other when made up into a complex tapestry of many hues?  Why did some black yarns seem washed out, paler, and less true to themselves, while others retained a deep, consistently saturated appearance?

To answer these questions, Gobelin employed distinguished chemist, Michel Chevreul as their director, who began a thorough and wide-ranging programme of investigative research. Chevreul carefully tested black yarns that had been dyed in Gobelin’s Paris workshops, comparing them to those that had been produced by competitor dyers in London and Vienna. There was, he concluded, no problem at all with Gobelin’s yarn dyeing process – the quality and consistency of the shades of black produced was excellent. So why, then, did some blacks appear to lack strength and saturation in the finished tapestries? After puzzling over this conundrum, Chevreul came up with an idea: could the darker or paler appearance of particular black yarns have less to do with the dyestuffs or dyeing processes than the eyes (and brains) of those looking at the textiles? Could black be seen differently in different contexts? Might black yarns simply appear paler when they were surrounded by other yarns which had been dyed in different shades?  And – by extension –  should the nature of dyed colour itself perhaps be thought of less as fixed or permanent, but rather as something that was always contingent upon adjacent and surrounding hues?  

Chevreul carefully shifted the focus of his research from industrial processes to visual phenomena, and began to develop the theory that was to change the world of colour: Simultaneous Contrast. 

At the heart of Chevreul’s theory is the idea that while looking at one colour, we are also seeing its chromatic opposite, or complement. 

Try staring at the centre of the yellow circle on the black background for 30 seconds. Now move your eyes to the centre of the white area on the right. You’ll see a bluish, purplish halo, blob,  or after image – as your eye casts yellow’s chromatic complement upon the bright, white background. 

You’ll see a similar effect from staring for 30 seconds at the red circle, which then casts a greenish complementary after image on the white background. 

Chevreul discovered that the way the human eye tends to see chromatic opposites, or complementary colours, also carried implications for perceptions of lightness, saturation, or hue. Looking at this selection of complementary colour pairs, you’ll note that the small grey square remains exactly the same shade of grey throughout, but has a very different appearance depending on which larger square of colour surrounds it.

Not only does each colour’s chromatic complement affect the way we interpret the grey of the grey square (we see, for example, the grey upon the yellow background as purple-ish, and the grey upon the purple background as yellow-ish), but each contiguous or surrounding shade also affects our perception of the grey square’s lightness or darkness (upon the yellow square, for example, the grey appears much darker than it does upon the purple). Here’s another example, in which the inner square is the same shade, but appears differently against the colour that surrounds it. 

When seen upon the green background, the inner, fuschia-coloured square appears to be a bright, light, hot pink, but against the orange, it begins to seem a purple of a darker, bluer hue. What’s happening here? Chevreul’s notion of simultaneous contrast points to one of the methods our brains have devised to process the complex visual information about colour that our eyes provide. The brain is basically a pattern-finding, discriminating, simplifying machine whose business is to continually categorise and separate things – in this instance, colours –  from one another. In order to separate and identify two adjacent shades, our brains simply tend to exaggerate their differences.  Our brains know that what is most different to green is its chromatic opposite or complement  – red. Therefore, when we see another shade that sits next to green, our brains are likely to over-exaggerate the redness of the second shade in order to separate it out, and make it appear more distinct. In the case of the example to the left, that difference is marked by tinting the fuschia of the inner square a hot, bright pink. Similarly, because our brains are well-trained in understanding orange’s difference from blue, so we over-exaggerate the blue-ness of the inner square in the example on the right, tinting and darkening it to purple, so that the separation between the two shades becomes that bit more obvious. 

Returning to the problem Gobelin’s managers had raised – the fact that some black yarns in finished tapestries appeared paler or less saturated than others – Chevreul’s theory of simultaneous contrast allowed him to demonstrate precisely why the issue seemed most acute when black yarns were placed adjacent to, or surrounded by, yarns of blue or violet hue. What was happening was that complementary shades were, in effect, tinting the eye’s perception of the depth of blacks that sat adjacent to blue or violet. When black yarns appeared next to violet yarns, they took on a yellowish appearance and when juxtaposed with blue, they appeared slightly orange-tinted. 

The implications of Chevreul’s discoveries were wide-ranging. He published his findings as an influential treatise, On the Law of Simultaneous Contrast of Colours (1839) and this and  subsequent publications, The Principles of Harmony and Contrast of Colours (1854) Chromatic Circles (1855) and Outline of a Way to Define and Name Colours (1861) – were rapidly translated into several languages and produced in multiple editions. Chevreul (who had no time for evocative colour names) went on to revolutionise the nomenclature of colour – categorising the more than 14000 different colours of the French wool dyeing trade into 72 kinds of shades, each of which had ten degrees of purity (referring to the amount of grey or black) and 21 degrees of intensity (ranging from from pale to super-saturated). He then pared down his numerical 72-shade system into a simplified Chromatic Circle and dreamed of producing a handy pocket-sized ceramic version to aid textile designers in their processes of colour matching (sadly, the manufacturers at the Vatican whom he approached to produce his pocket wheel felt its 72 graded shades were far beyond their capabilities). 

As interest in Chevreul’s theories spread, and as colour-curious international visitors flocked to his atelier, Chevreul would offer physical demonstrations of the wonders of his chromatic circle, by arranging tapestry skeins upon the floor in a gigantic woolly wheel whose glorious, graded hues inspired all who saw it. 

Chevreul was, first and foremost, a chemist, and it was in relation to the industrial processes of reproducing colour that his ideas of simultaneous contrast initially had most impact. For example, he was once called upon to appear as an expert witness in a lawsuit between a wallpaper manufacturer and his disgruntled client. The client had ordered wallpaper with a grey pattern on a green background but had objected to the printed pattern colour, on the grounds that it appeared to be of pinkish hue. The manufacturer argued that the grey was the precise shade that the client had originally ordered, while the client insisted that the shade appearing in the wallpaper was not grey at all, but pink. With the use of some removable white backgrounds, Chevreul demonstrated that both of them were, in fact correct: the manufacturer had indeed printed the exact grey shade the client had commissioned, but against an adjacent green, it could also appear to be pink! In his later publications, Chevreul showed manufacturers of coloured printed and dyed materials how they might address such problems by adjusting the relationship between background and pattern colours to neutralise these complementary visual effects. 

Chevreul operated in an industry dominated by organic dyestuffs, which was soon to be revolutionised by the chemical discovery of mauve, magenta and numerous other aniline shades that, to some extent, left chromatic classifications based on natural dyes behind. Yet his theory of simultaneous contrast went on to have a huge influence upon aesthetic discourse and artistic practice more generally as new generations of modern artists tried to think differently about colour harmony, contrast, and the effects of shades and hues. 

“There are colours that make each other shine, that make a couple, that complete each other,” wrote Vincent van Gogh to his sister Willemien in 1888 after reading Charles Blanc’s Grammar of Painting, a text which had drawn heavily on Chevreul’s ideas of colour complementarity and simultaneous contrast.

. . . with simultaneous contrast in mind, Van Gogh produced canvases of extraordinary vibrancy, like his famous pair of crabs. 

 . . .  Sonia Delaunay began to develop her own notion of Simultané, in which complementary colours, in bold juxtaposition, created the harmonies, rhythms and vibrations of a very distinctive modernist symphony.

. . . and in his Interaction of Colour Joseph Albers went on to sing the praises of Chevreul’s idea of simultaneous contrast, which, he wrote was “not just a curious optical phenomenon” but “the very heart of painting.” 

Michel Chevreul lived a life that was both extraordinarily long and extraordinarily industrious. Born in 1786, and living until 1889, he was, without doubt, one of the most creative and productive scientists of nineteenth-century France. In the 1820s, his research on animal fats led to the identification of what we now know as cholesterol; he was the first scientist to reveal that people with diabetes excreted glucose in their urine and his stearic-acid patent provided the formula upon which the modern candlemaking industry was based. Priding himself upon his avoidance of alcohol, his love of sleep, and his great good humour, Chevreul was also an indefatigable, inspiring teacher, who at the age of 97, still remained in his role as director of the dye works at the Gobelins tapestry manufactory. The world might commemorate Chevreul among the 72 scientists whose names are inscribed on the Eiffel tower, but knitters will remember him as the innovative yarn dyer, who changed the world of colour forever.

Thanks to Tom for simultaneous contrast illustrations

Further reading

Regina Lee Blaszczk, The Color Revolution (2012)

Laura Anne Kalba, Color in the Age of Impressionism: Commerce, Technology, Art (2017)