Reply to Joy Turner Luke’s Review

wavelengths(expressed in millicrons) are added together. The wavelengthsof the third color obtained from their mixture isequal to the sum of the wavelengthsof the twoconstituent colors.This charming nonsense compels an untenable conclusion. It implies that mixing red lightsof twodifferent wavelengths-say 645 millimicronsand 650millimicrons-would yieldlight witha wavelengthof 1295millimicrons. As figure 35-1 indicates, this isbeyond the upper extreme of the visible light sector of the electromagnetic scale. To begin with, the use of the term 'millimicron' tells us that she is out of touch with the field. Millimicron has been an obsolete term for many years. The correct word is 'nanometer ', abbreviated as 'nrn'. The statement that 'in additive color mixture the wavelengths of the constituent lights are added together' means that the color seen will be brighter than either constituent and contain both 645-nm and 650-nm wavelengths, not that the numbers assigned to the wavelengths should be summed. The only correct sentence in the quotation is her statement that 1295 nanometers is beyond the visible spectrum. Having demolished additive color, she proceeds to subtractive color: "When colored pigments are mixed together, the theory doggedly continues , the wavelengths (in millimicrons ) of one is to be subtracted from the wavelengths (in millimicrons ) of the other." No one ever said any such thing. A pigment exhibits color by absorbing some of the light falling on it. Mixtures of two pigments are called subtractive because the wavelengths absorbed by each are missing, i.e. 'subtracted', from the resulting mixture color. The mixture color is darker and probably a different hue than an additive mixture of the same colors would be. The situation is, of course, more complicated than this general statement. Pigment or dye mixtures in thin films, such as colored filters, are called simple subtractive mixtures because only the absorption characteristics of the constituent colors have to be considered. The appearance of a simple subtractive mixture is found by multiplying the wavelengths emitted by the light source by the wavelengths reflected by the colored specimen, and then multiplying the resulting products by the response of the standard observer, which means by the sensitivity of the 230 Current Literature average human eye. Each of these steps must be done wavelength by wavelength. An opaque mixture of paints is called a complex subtractive mixture because both the absorption and the scattering of light within the thicker paint film must be taken into consideration in order to predict the mixture's appearance. This is done through use of the Kubelka-Munk equations. Sloane read a lot of books but understood few of them. REPLY TO JOY TURNER LUKE'S REVIEW I wrote The Visual Nature ofColor because I grew weary of the claim, defended in some cases with astonished vehemence, that painters should be seen and not heard. I stand behind my considered belief that color, and color theory, warrant further study, and that many of the supposedly perfect explanations are not as perfect as defenders insist. Pointing to unanswered questions in any field except color theory creates no consternation. This field is unique in the number of hackles raised if anyone dares to say that not all the questions have been answered, and not all the answers are perfect. I would have expected that those interested in colorimetry, on a professional or casual basis, would have had the greatest amount ofintellectual curiosity about color. Yet those who argue that the theories about color are perfect already often come from the colorimetry camp or are its followers. Also, colorimetry, as a technology, is not of central relevance. New ideas about color are far more likely to come from the physical sciences, and will eventually filter down. The Munsell system dates from 1905, and may have been better in its original form, before it was buried in jargon and senseless elaborations. If nothing significantly new has come along in color theory for 86 years, that is not necessarily as happy a situation as Luke assumes. I appreciate the kindness of the editors of Leonardo in having my book reviewed . The tone of the review was unusual. Those of us who read book reviews want to know what the book is about and...