Any three paints that define a mixing triangle which encloses the center or
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colors, or mixing complements. These color combinations are both convenient (two paints are easier to work with than three) and
effective (two paints can often mix a darker neutral than three). Most artists memorize the important combinations as part of their color mixing lore.
I learned over my first few years of teaching myself to paint that much of the currently available information about mixing
complements in watercolor paints is inaccurate or incomplete. Sometimes the errors are trivial and sometimes they are large.
Because your mixing intuitions depend on your knowledge of mixing complements, I will go into this topic in depth. (Is there any other way?)
I approached this problem methodically, and an explanation of my test methods, with a complete listing of test results, are provided on this page. The image at right, which shows the mixing complementary tests for ultramarine blue (PB29), shows the gist. Each line
connects the measured color locations of ultramarine blue mixed with every warm pigment between cadmium yellow deep and cadmium scarlet. Any mixture that passes within the light gray circle has a minimum chroma of 5 or less, which is to most viewers indistinguishable from a "pure" gray; any mixture that passes within the dark gray circle has a chroma of 2 or less and really is a pure gray. (At least, watercolors marketed as white, gray or black have a chroma within that range.) Three lines fall within this circle:
raw umber, quinacridone gold, and benzimidazolone orange.
The chart below shows all the mixing complements between warm and cool
watercolor pigments (from ultramarine violet BS to chromium oxide green). (Again, this page presents the same information as a table. I've organized the table around the blue and green pigments, because there are fewer of them.)
near neutral mixing lines for ultramarine blue
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the watercolorist's mixing complements
pigments that make "pure gray" mixtures are joined by dark lines, "near gray" mixtures by light lines; see this
page for the same information in tabular form
Before you panic: this diagram is meant to make a single point. If the hue relationships
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the chart. This is obviously not the case!
The real problem here is the ugly mess called subtractive color mixing, which has some memorable peculiarities:
• Nearly all the mixing complements for blues and blue greens are limited to the warm colors from carmine to deep yellow. That is, most mixing complements lie around the warm/cool color contrast, which is really the "mother of complementaries." This is
emphasized by the way the mixing lines tend to slant toward the red orange center of the warm color range (around burnt sienna).
• With few exceptions (yellow ochre and other dull deep yellows), yellow has no role as a mixing complement. This is because yellow reflects both "red" and "green" light, and it is extremely difficult to get a reddish blue or blue violet color that can exactly cancel out both parts of the spectrum equally.
Is Stephen Quiller incorrect to say that ultramarine violet and lemon yellow make a pure gray mixture? Yes. The bluish shade of ultramarine violet (PV15) he recommends (made by M. Graham or Blockx) produces a cadaverous near gray with any yellow hue — lemon yellow through deep yellow. But these mixtures are actually a greenish gray, not a true gray. They appear gray, however, because we tend to choose a cool color as a "true"
gray. I used a spectrophotometer to measure my test mixtures; Quiller used his eyes.
• The warm hue mixing complements for most blue or green pigments cover a large hue span.
This means that paint mixing cannot
identify unique complementary colors for any blue or green. Take phthalo green BS (PG7) for example: you can get a dead on dark gray by mixing it with pyrrole scarlet (PR255) or with perylene maroon (PR179).
So is the "true" complementary color for phthalo green a bright scarlet or a dull
carmine? (Quiller pairs phthalo green BS with quinacridone rose PV19, which produces a
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• Some of the mixing complements
contradict color wheel logic. Compare, for example, the mixing complements of prussian blue (PB27) and phthalo turquoise (PB16).
The perfect mixing complement for prussian blue is venetian red (PR101), and the best complement for phthalo turquoise is perinone orange (PO43). But phthalo turquoise is much closer to green than prussian blue, and
perinone orange is also closer to green than venetian red: as the blue hue moves
counterclockwise around the color wheel, the complementary color moves clockwise! You just can't get that to make sense on a color wheel.
The truth is that you can't show mixing complements as a color wheel. No matter how you tug and pluck, you can't unravel the mess created by the substance uncertainty of real paints. The only way to cut through the knot is to work with the color relationships defined by additive color mixing, as I've done with my artist's color wheel, and learn the mixing complementary relationships by rote for the paints actually on your palette. Paints you don't use you don't have to know about.