Though often dismissed as misguided and ill-informed, in terms of its scientific understanding of the physics of light, Johann Wolfgang von Goethe’s work on color betrays an imaginative approach that knows no equal. His polemical rants against Newton (ones that he came to regret later in life) often obscured his contributions to the more perceptual aspects of color. In some ways, the adoption of the Standard Observer in color science today owes a debt to Goethe’s rich and varied experiments on the phenomenology of color perception. And though his explanations and theories can appear wanting, the sheer force of his imaginative investigations have had a lasting effect on the subject of color ever since.
One of the strangest and most fascinating of Goethe’s investigations involves what is known as the dark spectrum (also known as the inverted spectrum and the Goethe spectrum.) What at first sight might seem like an absurd and logical impossibility, the refraction of darkness has, it turns out, some interesting and curious things to say about our perception of color. The typical spectrum, as exemplified in the work of Isaac Newton, involves passing a beam of white light through a prism, and viewing the resultant array of colors that pass through the other side. Newton coined the term spectrum (from the Latin, meaning apparition) to describe this well-known phenomenon, and labeled the colors of the spectrum, red, orange, yellow, green, blue, indigo and violet. Goethe, on the other hand, felt that darkness was just as important as light, in the creation of color. In fact, he felt that all colors were an admixture of light and dark, an idea that went back to Aristotle. In his Theory of Colors (Zur Farbenlehre) of 1810, he proposed a series of experiments that he felt provided a more complete and comprehensive theory of color than Newton’s. One such experiment (fig.1) posited the idea of passing darkness, not light, through a prism, and noting the particular ‘spectrum’ that appeared on the other side. What Goethe found was a spectrum that was composed primarily of what we would today describe as cyan, magenta and yellow with intermediate colors of red and blue.
Fig. 1. J.W. Goethe, Theory of Colors. Plate IV fig.2 (1810) Trans. C Eastlake. Image source: Wikimedia Commons
This effect can easily be produced by projecting the image of a dark line on a white background through a prism (fig. 2), or by placing an object in front of the prism.
Fig. 2. A black circle image projected through a prism. Image source: author
From the standpoint of color science, darkness is the absence of light, and so cannot be refracted. To be fair, Goethe did not believe that the visible colors of his, or Newton’s spectrum for that matter, were the result of differential refraction. Instead he believed that color was an admixture of dark and light, as mentioned previously, and occurred only at the boundaries or edges of light and dark. He maintained that what we see in the middle of each of the two spectra, green (Newton’s) and magenta (Goethe’s), resulted from the mixing of their borders. Goethe believed that these two spectra proved the polarity and complementary nature of light and dark, a theme picked up many of his followers and adherents. No doubt they do display a striking symmetry: one light, one dark, one composed primarily of the additive primaries (RGB) the other of the subtractive primaries (CMY), and both seemingly produced in similar ways. But the effect exhibited in the dark spectrum, is produced by the light that surrounds the dark shape, as it refracts differentially. Because the darkness is a ‘gap’ in the light passing through the prism, each refracted wavelength will contain its own corresponding ‘gap’ and will displace differently, according to its wavelength. By additively combining the remaining wavelengths found at such gaps, the resultant colors will appear, as can be seen in the following diagram (fig. 3).
Fig.3. By refracting the basic components of white light (RGB) the dark shapes contained in each, displace (horizontally) in such a way that the remaining wavelengths additively mix (vertically) to produce the secondary colors that are perceived when passing “darkness” through a prism. Image Source: Dr. Louis Adams.
But though he might have been wrong about the physics of his experiments, his imaginative approach to color is not without merit. Goethe’s unorthodox approach encourages us to re-imagine color in ways that might lead us to question what is accepted knowledge, and thereby open the door to a line of questioning that is as relevant today, as it was in Goethe’s time. Though his science may be ‘wrong’, the example of the dark spectrum leads to something about color perception that has received very little attention; one that may challenge some of the more established ‘truths’ about human color perception. But for that, I am afraid I will have to leave you in the… dark, until the next installment!