color notation
https://color.adobe.com/create
From the Munsell Book: (color theory)
from http://www.handprint.com/HP/WCL/color14.html (color mixing)
3 de noviembre de 2019
split primary palette
Color mixing strategies inevitably leads to the issue of special paint selections or palette designs intended to make color mixing simpler, more effective or downright foolproof. Perhaps the most popular among these is the split primary palette.
The Dogma. If the artist limits his paint selection to the traditional primary triad palette, then the saturation costs in secondary color mixtures (orange, purple and green) are so severe that even some artists committed to their primary color dogma look for a way to reduce them.
The common remedy has been to split each "primary" color into a pair of colors, each leaning toward one of the other two "primaries." So the single primary yellow paint is replaced by two paints: a warm (deep) yellow that "leans toward" (is tinted by) the red "primary," and a cool (light) yellow that leans toward blue. Similar replacements are made for the other two "primaries," which doubles the palette from three to six paints.
the split primary palette
the version proposed by Nita Leland
According to Nita Leland, a representative split primary palette would consist of:
• warm blue : ultramarine blue (PB29) (leans toward red)
• cool blue : phthalocyanine blue GS (PB15:3) (leans toward yellow)
The color theory logic for these substitutions goes like this: a yellow that leans toward blue is a yellow that actually contains blue, and a blue that leans towards yellow is a blue that contains yellow. So the blue and yellow reinforce each other when mixed to make green. But if either color leans toward red, then red is carried into the mixture through the yellow or blue paints. This isn't good, because mixing all three primaries creates gray or black, and this dulls the remaining green mixture.
This becomes a rule: when mixing two primary colors, choose the paints that lean toward each other to get the most vibrant mixture. The slogan is, "never put the mixing line across a 'primary' color" — that is, don't choose either two primaries leaning toward or tinted with the third primary, because mixtures containing all three primaries mix to gray. Split primary advocates call these mixtures "mud."
Of course, the painter can intentionally choose one or both of the primaries leaning toward the third primary, if he wants less intense or near neutral mixtures. But then color theory painters will call his paintings mud.
The Critique. Where did these muddled recommendations come from? Straight out of the Newtonian color confusions of the 18th century. Essentially the same color concepts appear in the color wheel text by Moses Harris, and are accepted without serious challenge in Michel-Eugène Chevreul's The Principles of Color Harmony and Contrast (1839). Chevreul describes color mixing beliefs that must have been widely accepted by artists of his time; one passage is worth quoting at length:
We know of no substance [pigment or dye] that represents a primary color — that is, that reflects only one kind of colored light, whether pure red, blue or yellow. ... As pure colored materials do not exist, how can one say that violet, green and orange are composed of two simple colors mixed in equal proportions? ... Instead we discover that most of the red, blue or yellow colored substances we know of, when mixed with each other, produce violets, greens and oranges of an inferior intensity and clarity to those pure violet, green or orange colored materials found in nature. They [the authors of color mixing systems] could explain this if they admitted that the colored materials mixed together reflect at least two kinds of colored light [that is, two of the three primary colors], and if they agreed with painters and dyers that a mixture of materials which separately reflect red, yellow and blue will produce some quantity of black, which dulls the intensity of the mixture. It is also certain that the violets, greens and oranges resulting from a mixture of colored materials are much more intense when the colors of these materials are more similar in hue. For example: when we mix blue and red to form violet, the result will be better if we take a red tinted with blue, and a blue tinted with red, rather than a red or blue leaning toward yellow; in the same way, a blue tinted with green, mixed with a yellow tinted with blue, will yield a purer green than if red were part of either color. [1839, ¶¶157-158; my translation]
There you have the color ideas behind the split primary palette. Unfortunately, most of them are factually wrong or logically unrelated.
Chevreul is criticizing the idea that "primary" colors can be represented in paints by observing that these primary paints can't mix all the hues of nature with sufficient intensity or chroma. From that he concludes that paint pigments do not reflect "only one kind of light". A yellow primary paint must reflect "yellow" light mixed with some "blue" or "red" light, which dulls the pure yellow color. As we can't avoid this color pollution, we minimize it by mixing colors tinted with each other — so the thinking goes.
However, paint colors do not simply represent spectral "colors" as Chevreul believed: a primary yellow paint does not just reflect a lot of "yellow" light. Nor is color "in the light" as colored light; there are no "magenta," "red violet" or "purple" wavelengths in the spectrum, so those colors cannot be "in" the light. The same surface colors can result from very different light mixtures: yellow results from a "red" and "green" mixture, and red violet from a "blue violet" and "red" mixture. These confusions were clarified later in the 19th century through the popularizing science books by Hermann von Helmholtz and Ogden Rood. Surprising, then, that the "paint color equals light color" fallacy is still widely believed by painters today — Michael Wilcox teaches it as the basis of his color mixing system.
In addition, you can never find a paint, a crystal — or a light — whose color is "pure enough" to match a primary color. This is because primary colors are always imaginary or imperfect: they can never be matched by visible lights or paints, and visible lights or paints can never mix all possible colors. The reason for this lies in the design of our eye — in the overlapping response curves of the L, M and S light receptors. The "impurity" of the light reflected by the paint certainly aggravates the problem, but is not the cause of it. The "color theorist" dogma that paint mixing problems arise because paints are "impure colors" is bogus.
Choosing two paints or inks that are more similar in hue does increase the intensity of their mixture, as Chevreul says. But these saturation costs again have nothing to do with the contamination of one primary color with another. They appear even when we mix monochromatic (single wavelength) lights that are completely free of tint by any other hue. In fact, mixing pure spectral lights was how Newton discovered saturation costs in the first place!
In brief, the split primary palette is based on 19th century color ideas that have nothing to do with the facts of color perception and color mixing as we understand them today.
The Demonstration. But the pragmatist may say: who cares? Just because the justification is murky doesn't mean that the split primary palette isn't an effective selection of paints.
Fair enough. So let's hold the split primary palette to its two key claims: (1) that red and blue (rather than magenta and cyan) are the most effective primary colors; and (2) that splitting these primary colors allows us to mix the most vibrant secondary colors (orange, purple and green). It's easy to show that both these claims are false.
A "pure" red or blue makes an ineffective primary color because these colors fail the basic requirement for a subtractive primary paint: it must strongly stimulate two receptor cones but not the third. A pure red and pure blue paint mix dark, grayed purples, for example, because they have almost no reflectance in common; for the same reason, the blue and yellow make very dull greens. So the split primary palette starts out with an inaccurate definition of the primary paints most useful for subtractive color mixtures.
We can evaluate the second, "vibrant color" justification for the split primary palette by comparing it to any other palette of six paints, for example the secondary palette, to see which paint selection is superior. There are two ways to do this.
A simple "back of the envelope" approach is to print out a copy of the pigment map presented on the CIECAM aCbC plane, identify on this map the location of the pigments used in all paints in the palette (use the complete palette to identify specific pigments), then connect these pigment markers to form the largest possible, straight sided enclosure (see examples below). The closed area is the gamut of the palette — the approximate range of hue and saturation that it is possible to mix with that selection of paints. The palette with the larger gamut will create a wider range of color mixtures.
comparing the gamut of two palettes
split primary palette (left) and secondary palette (right)
on CIECAM aCbC plane
on CIECAM aCbC plane
The split primary palette (at left) creates a narrow lozenge of color mixtures that is skewed toward the "warm" colors of the palette, and puts the heaviest saturation costs (dull mixtures) in the mixed greens and violets. In contrast, with the equally spaced secondary palette (at right), we get a substantially increased range in color mixtures. This is because a single intense pigment anchors each primary and secondary hue, which pushes back the limits of the color space as far as possible (particularly on the green side). Same number of paints, very different gamuts.
The alternative (and better) way to compare palettes is to use each one to mix the twelve colors of a tertiary color wheel. Display these mixtures either side by side or as matching paint wheels (below), and see what you get.
comparing paint wheels made with two palettes
split primary palette (left) and secondary palette (right)
This side by side comparison confirms the gamut differences identified with the palette schemes. The mixed red orange in the split primary palette (left) is so dull it is close to brown; the purple is dark and grayish, and the mixed greens are drab across the entire range. In contrast, the secondary palette (at right) is obviously much brighter in the greens, produces a more evenly saturated range of warm hues, and gets juicy purples as well. If you don't want "mud," then the split primary palette is not the one to choose!
Can we fix these problems by changing the selection of split primary paints? Yes we can, and the solutions people choose are revealing. The palette scheme for the Wilcox six principle [he means principal] colors shows that his split primaries have turned into the secondary color wheel, but with green omitted in order to provide two very similar yellows.
palette scheme for the Wilcox six principal colors
from "Blue and Yellow Don't Make Green" (2001)
Wilcox has widened the split between the red and blue primaries to the point where they are completely different hues (scarlet and magenta, or blue violet and green blue) — yet he still hangs onto his two similar "primary" yellows. This is a funny and revealing example of how a color dogma accepted without question (you must use primary colors!) can trample on color mixing common sense (hey, mixtures look so much brighter if you add a scarlet, blue violet and green paint!).
Not only have we found that the split primary palette fails to meet its claims, and its color theory justifications are inaccurate, I've proven by demonstration and explanation that the secondary palette is the superior mixing system. And because it lets the painter choose many different paints for the three contrasting pairs of complementary pigments, the secondary palette offers the largest gamut and value range, and the greatest alternative choices of transparency, staining, granulation, texture, and handling attributes in paints that are possible with a six paint palette. Try it for yourself and see.
unequal color spacing
The logic of the split primary palette contains the germ of an important idea: that you can explicitly control the saturation costs of your color mixtures by the grouping or spacing of the most saturated paints in your palette.
Increasing the color wheel or hue circle distance between two paints increases the saturation cost or dullness in their midpoint mixtures, and within the "primary" triad or split "primary" frameworks this effect is most pronounced in orange, purple and green colors. By manipulating the bright or dull mixing potential of these purples and greens, the artist can shape the fundamental color dynamics of his painting palette.
unequally spaced colors and the implied illuminant
The color wheel schematic (above) shows the two main variations painters are likely to use: when the illuminant — the color of light — shifts warmer (toward longer wavelengths, becoming yellowish or reddish) or greener (the color of intense noon sunlight).
The basic principle is that when the illuminant has a distinct color, it brightens similar hues and dulls complementary hues.
Warmer Color Shifts. In this case, typical of late afternoon light or artificial light from a candle or incandescent light, warm colors become more saturated and cool colors become darker and duller.
This suggests choosing warm color (red to yellow) paints that have higher saturation and cool color (blue) paints that are relatively darker and duller. Burnt sienna would be replaced by cadmium orange, and phthalocyanine blue by iron [prussian] blue or a red shade of phthalo blue.
Provided the light yellow is not too pale (greenish), all mixed yellows will be very saturated and light valued. If the "cool" red is shifted from a bright quinacridone magenta to quinacridone red, and the "warm" red into red orange, the saturation of mixed warm hues will be consistently at maximum saturation.
The greens mixed from yellow and blue will be moderately dull and somewhat dark. These muted greens yield dominance to the more intense reds and oranges, reducing the fundamental visual tension between red and green. Because all the greens must be mixed, they will be more varied and interesting.
The blue paints are typically grouped close together, so the mixed middle blues will be relatively bright, but quickly become muted as they are mixed with the "cool" yellow or red. This gives the range of blues a chromatic emphasis around the sky color, surrounded by a range of less intense green blue and blue violet mixtures for foliage and shadows. The mixed violets will be somewhat dull, and dull dark blues (the visual complements of yellow or red orange), not purples, should be used to tint shadows.
Greener Color Shifts. A "green" color shift is characteristic of colors under intense noon sunlight. Daylight does not appear green to our eyes because of the color balancing effect of chromatic adaptation, but the relative color emphasis that results can be modeled by different palette choices.
The main effect of this greening is to brighten greens and to dull purples (because purples are the complementary hue of the light). As there are few useful purple or green pigments, the most common method to produce this bias is to shift the yellow and blue paints toward each other — by choosing a lemon or greenish yellow as the "cool" yellow, and a greenish or turquoise blue for the "cool" blue — thereby increasing the saturation of green mixtures. The greenish blue should also be somewhat lighter valued, if possible: cobalt turquoise or cobalt teal blue (PG50) are very useful alternatives.
In contrast, the hue circle distance between the "cool" red and "warm" blue should be increased, and one of the colors should be dark valued, if feasible — for example, by choosing a phthalo blue red shade or a quinacridone carmine. These will produce dull dark purples that are usefil to tint shadows with the complementary hue of the illuminant color.
Other imbalanced distributions are possible, which might contrast a broad range of blues against dull earths, vibrant greens against dull reds, and so on in many combinations. But the palette shown in the figure, with most of the saturation costs in the violets and greens, is one of the most popular; dozens of palettes are variations on it.
Why not just choose a large number of paints that are very closely spaced all the way around the color wheel? You can, if you want. These colorist palettes are useful for a bright and lively style of painting that specifically does not give the impression of a certain kind of light. The point is that saturation costs can buy you expressive resources, particularly in landscapes and portraits. Forcing some color mixtures to be dull confers a light giving power to the pure colors they are mixed from, which can create a deep color harmony across the value structure of a painting.