Welcome to

by Linda Carson

big black pig studio
98 King St. N., Waterloo Ontario Canada
www.bigblackpig.com

Colour Theory: The Gory Technical Details

The idea that yellow, blue and red are primary colours is a useful simplification of how colour works. It'll do, for most practical purposes. When a quiz—or a quiz show—asks "What are the three primary colours?" the answer they're looking for is "Yellow, blue and red." If you're satisfied with that, hit the back button right now and avoid messing up a good thing...

...because sometimes the Real Answer is "yellow, cyan and magenta." As if that's not bad enough, other times the Real Answer is "red, green and blue."

What is Colour, Really?

Light is an electromagnetic wave. If we can see an object, that's because it is giving off or reflecting light. The sun gives off light. I reflect light.

When sunlight shines on me, I can reflect it, absorb it, or transmit it. You see me because some sunlight reflects off me. I stay warm because I absorb some sunlight. I see the sun because of the sunlight transmitted through my corneas to my retinas.

"Light" is the limited range of electromagnetic wavelengths that are visible to the human eye. (Electromagnetic waves we don't see include x-rays, infrared, ultraviolet, and radio.) "Colour" is our kinda nifty ability to distinguish one wavelength of light from another, just by looking at it. If the light we see reflecting off an object is a mixture of all the visible wavelengths of light, the object looks white. It's more common, however, for an object to reflect only some of the wavelengths of light, while absorbing the rest. The combination of wavelengths of light reflected by an object show us its apparent colour. An apple looks red because it reflects red light (and absorbs the other visible wavelengths).

Mixing Colours of Light Emitted: Additive Mixing

When colours (wavelengths) of light are mixed, we call it "additive mixing." This is what happens when two coloured spotlights shine on the same patch of stage floor. The three primary colours of light are red, green and blue.

Red light and green light, mixed, create yellow light. Green light and blue light, mixed, create cyan light. Red light and blue light, mixed, create magenta light. Mixing all the colours—or wavelengths—of light makes white light. That's an everyday event; we're bathed in white light all day.

Mixing Colours of Light Reflected: Subtractive Mixing

When two coloured materials are mixed, we're actually reducing the number of wavelengths of light reflected by the mixture. For example, red stuff absorbs all the wavelengths except red. Blue stuff absorbs everything but blue. Mixing blue stuff and red stuff together creates a material that absorbs almost everything. That's why mixing colours of paint (as opposed to light mixing) is called "subtractive." It reduces the amount of light and the wavelengths reflected.

Most materials reflect an assortment of wavelengths of light, giving them a colour that's a mixture.

Now here's where it gets disturbing. Innocent schoolchildren and art students have been taught for years about Red/Yellow/Blue, but the optically pure primary colours are actually cyan, magenta and yellow. The physicists are pretty certain about this even though it disagrees with art classes all over the world. Cyan/Magenta/Yellow... We were close. Yellow's right. Cyan is certainly one sort of blue. But magenta? Well, yes, magenta. It's a lurid, pinky sort of colour, which makes it a red, after a fashion.

My first evidence that the physicists might be right is that magenta is the colour printers have been using for decades to create full-colour images, one of the "process colours" used in the CMYK system (which stands for Cyan, Magenta, Yellow and blacK).

If this is true, red is actually a secondary colour and you can make it by mixing pure magenta and pure yellow 50/50. Orange is a tertiary colour between red and yellow.

My second evidence came from buying true primary magenta and yellow, then mixing them together. I got red! So I guess the physicists aren't nuts after all.

There are some things about this new understanding of colour that are reassuring. First, this tidies up the relationship between additive and subtractive colour mixing. They are inverses of one another. Check out the diagrams. Second, I finally realized why I've had so much trouble mixing nice purples over the years. Since red is really a secondary colour with a lot of yellow in it, all my purples were muddied by mixing in the complementary colour.

Mixing Colour in the Real World

Why didn't painters notice that red isn't a true primary colour? It's not a conspiracy of silence. It's the reality of pigments. The colour in paint doesn't begin with wavelengths of light, it begins with ground-up particles of stuff—whatever coloured stuff we can find or make that doesn't fade or alter with time, light exposure, or contact with other materials. Painters live in the real world, and in the real world, we work with pigment, and paint.

For painters to determine hands-on that a colour is primary, they need to practice working with that colour. If you don't have magenta—a lightfast, stable magenta pigment—then you can't use it. And without magenta, red is a primary colour, for all practical purposes. If you don't have magenta then you certainly need a red paint to produce any reddish colours. That makes red a "primary."

Permanent magenta colours became available in my neighbourhood only in the late 1990s. In retrospect, I understand why watercolourists loved their rose madder and Holbein Opera so much, even though the colours didn't last. They made good primary magentas.

If you were going to be trapped on a desert island and could only take five tubes of paint, you should take black, white, yellow, cyan (blue) and magenta (red). The practical reality is that painters usually keep two or more reds around. A cool red such as alizarin crimson or quinacridone will make clear purples. A warm red such as cadmium or napthol will make clear oranges. Similarly, it's handy to have warm and cool yellows and blues available.

P.S. And this painter is buying and testing permanent magentas to find clear true primary colours to add to her own palette.

Back to the main lesson?

Loosely translated, that means:
"Please don't copy this material or redistribute it in some other form, for any reason. This is my livelihood."