Top Left: Alizarin Crimson, Top Right: Cadmium Red, Bottom Left: Magenta, Bottom Right: Permanent Magenta
A number of artists on the Internet who demonstrate their color mixing abilities embrace a limited palette of cadmium red, cadmium yellow and ultramarine blue as their foundational set of colors and add burnt umber and white to top off their 5-color palette.
Other artists expand their palette to include 9 colors*. In this Syntax essay, we will focus on how only red pigments will function in a 9-color arrangement. Since a written color mixing demonstration makes no sense, I thought it best to dazzle you all with some scientific graphs. Long ago, I captured spectral signatures of a wide variety of colors. I examine them on occasion when a color mixing questions arises.
I noticed that when challenged with mixing a particular purple-red color, the use of cadmium red and ultramarine blue initiated an exhausting number of tweaks with other colors, but ultimately, I never achieved a satisfying match. While considering myself to be average in color mixing/matching ability, I was stumped by this purple-red color. I was trying to match a commercial paint sample color card obtained from a hardware store. Given this challenge, I knew that the universal color mixing pigment set that paint companies provide retailers to make their paints match their color cards or a color that a customer brings to them, they use a number of synthetic organic colors to boost and expand the range of hues that can be obtained. Inorganic pigments like cadmium red don’t stand much of a chance in competing with many vibrant synthetic organics that display an enormous depth of chroma. I knew I was working with a handicap when only using inorganic metallic-based pigments.
Having met my color mixing “brick wall,” I took out a tube of quinacridone magenta and within 3 or 4 minor adjustments, I matched the paint sample spot on. OK, so why did this happen and why was it so easy?
The answer lies in the bias that all colors have within them. These biases or underlying reflectance hues are difficult to see in mass tone, but once a pigment is mixed with white or is incorporated with a combination of other colors, the bias of a color such as quinacridone magenta becomes apparent.
We can also prove this using the spectral reflectance of a color. A spectrophotometer is used to measure the variety of wavelength that are reflected by a color. As humans, we see color in the electromagnetic range of 380 nanometers (violet) to around 750 nanometers (red.) Lower than 380 nm is ultraviolet and beyond 750 is infra-red or heat energy.
When looking at the 4 spectra images illustrated in this essay, note that the height of the line indicates how much reflectance of the color is being transmitted. To help see what part of the spectrum is being reflected, I have placed a color bar at the bottom of the x axis of the graph. If the line is higher on the graph, more color from that part of the visible spectrum is being reflected. Got it? Let’s see what is happening.
So, what makes Cadmium Red so ineffective in making a purple-red color with a high chroma? Let’s start by comparing it to an old trusty standard red color that some artists still use, Alizarin Crimson. Examining its spectra, Alizarin Crimson displays a small but significant amount of blue reflectance. More importantly, it had little to no green reflectance. That allows Alizarin Crimson to mix wonderful red, orange and purple mixtures because the lack of green reflectance (red’s complement) in the pigment does not mute the redness coming from alizarin mixtures. The lack of red’s complement make alizarin a strong and versatile color.
Now look at Cadmium Red. It has similar characteristics to Alizarin Crimson but it lacks the blue reflectance alizarin conveys. Lacking any green component in the reflectance, it is a powerful red we know and love. But lacking any blue reflectance, it has a difficult time making any knock your socks off, burn your retina, purple hues.
Now look at the Magenta and Permanent Magenta spectral. Bingo! Both colors have strong blue reflectance and little to no green reflectance. Magenta has a fairly strong yellow-orange reflectance so when mixed with blue to make purples, it will be somewhat more muted than permanent magenta can deliver. Permanent Magenta has little yellow or orange reflectance and a strong amount of blue reflectance so it can make outstanding purple and a broad range of red and orange mixtures.
So, science can be fun? Right? A reflectance spectral reading confirms what we know as artists when mixing colors. The spectra tell us that there is a right “tool” for the job. Attempting to make a high chroma purple using cadmium red and ultramarine blue defies the physics of the pigments involved. This does not mean we should abandon any pigments. I still love Cadmium Red for what it can do. I would never give up Ultramarine Blue for anything. I just won’t try to make a vibrant magenta rich purple-red using those two colors.
We will look at other hues and their spectra in future editions of the Syntax of Color. Stay tuned.
The Syntax of Color
*The 9-color palette can include the following or some variation on this group: White, Yellow Ochre, Burnt Umber, Cadmium Red, Quinacridone Magenta, Ultramarine Blue, Cobalt Teal and Phthalocyanine Green.