Color Theory

THE enigma of color has attracted the interest and attention of many of the most gifted intellects of all time. Aristotle, Grimaldi, Newton, Goethe, Hegel, Schopenhauer, Young, Maxwell, Helmholtz, Hering, and SchrÐ"¶dinger all have been intrigued by color and have contributed to our knowledge of it.

Aristotle based his view of color on the observation that sunlight on passage through, or reflection from, an object is always reduced in intensity, or darkened. Since by this operation colors may be produced, he viewed color as a phenomenon arising out of the transition from brightness to darkness, which in a sense it is; or, stated less clearly as it usually is, Aristotle viewed color as a mixture, or blend, or commingling, or superposition, or juxtaposition of black and white. An essential part of this view, widely held up to Newton's time (1642 to 1727), is that all true and pure light, such as light from the sun, has no color, and color must be some sort of constituent or material permeating opaque and transparent objects and media, capable of altering or degrading the pure light incident upon them. Some doubts as to the correctness of Aristotle's view began to arise early in the seventeenth century because of the discovery of what

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we now name interference colors - colors of thin films, such as soap bubbles - which change markedly with angle of view. These films seem to have every kind of color in them at the same time and to contaminate the incident sunlight in different ways depending on thickness of the film and direction of passage of sunlight through it.

The discovery in 1665 by Newton that light from the sun could be bent to varying degrees by a prism so as to produce a spectrum of colors ranging from red (rays least bent), through orange, yellow, green, and blue, to violet (rays most bent) provided the basis for rejecting Aristotle's view that color comes from objects and permitted substitution for it of the view that color is a property of light. This view has been supported by the great advance in our understanding of the various physical phenomena (interference, scattering, and diffraction as well as refraction and absorption) by which color may appear. This view is, indeed, a view widely held today. It states that wavelength composition of a light beam serves to define its color, and it suggests that physics holds the key to the enigma of color.

We must pause here to make clear that this extreme view that color is a property of light, and of light alone, though it arose among Newton's followers arid was based on his discovery,

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was not shared by Newton himself. He states in a passage, lately much quoted, from his Opticks: "And whenever I seem to speak of radiation or rays, coloured or imbued with colour, I should like it always so expressed that it does not sound philosophical or special, but intelligible to the general public; since those ideas are accepted which people, watching experiments of this kind, can themselves comprehend. Indeed, rays, properly expressed, are not coloured. There is nothing else in them but a certain power or disposition which so conditions them that they produce in us the sensation of this or that_colour." Newton's view that color is a sensation is also widely held today, but, though Grimaldi, the great Italian pioneer in optics had already expressed a closely similar view in tile very year (1665) of Newton's discovery, Newton's followers quickly forgot it.

It must not be supposed, either, that Newton is responsible for the great oversimplification that wavelength of light determines color. Newton's view of light was that it consists of corpuscles or small particles flying through space away from every source of light. The wave theory was not substantiated until many years after Newton's death in 1727 by Thomas Young (1773 - 1829) who successfully maintained from his experiments on interference that "radiant light consists of undulations of the luininiferous ether." Independently of Young, tile French physicist,

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Fresnel (1788 - 1827) disproved Newton's corpuscular theory of light by experiments supporting the view that light is due to wave motion, and that these waves are perpendicular, or transverse, to the direction of propagation of the waves. The wave theory, once established, explained in a simple and brilliant way the colors produced by scattering, diffraction, interference (for example, in thin films), polarization, and refraction. It became easy to ignore Newton's view of color as a sensation, usually, but not always, originating out of raÐ'­diation, and to say simply that waves of length 400 to 450 nm (billionths of a meter) are violet; 450 to 480, blue; 480 to 560, green; 560 to 590, yellow; 590 to 620, orange; and 620 to800 mm, red.

To Johann Wolfgang von Goethe (1749 - 1832), student of the arts, theatrical director, and widely acclaimed author of the master works Iphigenia at Taurus, Egmont, and Faust, this simple theory of color was the result of mistaking an incidental result for an elemental principle. His study of color phenomena, which extended over many years, had led him to an explanation of color more akin to that of Aristotle than to the new physics that he did not understand. In a period of his life described by literary critic as "a long interval, marked by nothing of distinguished note" he wrote out a clear and sysÐ'­

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tematic description of all of his extended observations of color phenomena interspersed with the arguments supporting his explanation of them. Instead of attacking the physicists of his own day, who deserved it, for their neglect of the subjective aspect of color, he attacked their predecessor, Newton, who did not. All of physics, he implies, had got off to a misguided start because of its reliance on Newton. He says (Paragraph 726) : "A great mathematician was possessed with an entirely false notion on the physical origin of colours; yet, owing to his great authority as a geometer, the mistakes which he committed as an experimentalist long became sanctioned in the eyes of a world ever fettered in prejudices." Again (Paragraph 725): "The theory of colours. . . has suffered much, and its progress has been incalculably retarded by having been mixed up with optics generally, a science which cannot dispense with mathematics; whereas the theory of colours, in strictness, may be investigated quite independently of optics."

Of his own theory Goethe was supremely confident.