Nov 7, 2011

Color Basics: Subtractive color

It is easy to be confused as to why we call the color system we use when painting a subtractive color system. After all, we are adding different colored paints to each other in order to get the desired color and it seems natural to want to think of it as an additive method of creating color. The trick to understanding why it is subtractive is to look at the characteristics of light. In doing this, we will understand we are relying on the subtractive qualities of the paint to get our desired color.

Today, we are going to look at how light is affected by the pigments in the paint to better understand the subtractive color system.

Let's begin,

Subtractive Color 

Subtractive Color

Someone familiar with the RYB color wheel is already familiar with an example of a subtractive color system.

In the RYB color system, we are using the pigments in the paint to subtract certain frequencies of light out of the source light so that the surface reflects the color we want.

Look at the diagram to the right. The center of the three overlapping colors is black. This is illustrating the fact that all the different color frequencies of the light are being absorbed by the pigments in that area.

Notice that the area surrounding the three colors is white. This is illustrating that the pigment of the paint does not absorb any of the light, reflecting all of the frequencies of the light back to the viewer. The surface is not subtracting any of the frequencies out of the light, keeping it white.

Finally, each color field is only reflecting the light frequency of that color.

A Closer Look: Our setup

To the right is the illustration we will use to demonstrate the concept of subtracting the frequencies of light to create a color.

The light bulb is emitting white light and the surface is painted with a red dot to illustrate how red paint will affect the light.

Spectrum of Light

Light is part of the larger range of electromagnetic radiation that is measured in wavelengths. It is the wavelengths or frequencies at certain ranges that allow us to see. This is visible light.

A light source containing the full range of frequencies of visible light allows for all the possible colors to be seen. This is because within this light there are all the different wavelengths of light and each color we see corresponds to one of those wavelengths or frequencies of light. This type of light is called a full spectrum light.

An easy understanding of full-spectrum light is to just imagine that the light is made of many different colored lights mixed all together.

In order to see a particular color from this light, we need to separate the frequency of light that corresponds to the color from the other wavelengths of the white light.

In this next illustration, I have separated the full spectrum light into different wavelengths represented by the three primary colors being emitted from the bulb. (Actually, there are more than three wavelengths, but for simplification, I will use just the three.)

Light Absorbed

When the light reaches the surface the white part will reflect back all the frequencies of light. The red area will absorb all of the frequencies except the wavelength that corresponds to the color red. This wavelength will be reflected from the surface. Allowing the viewer to see a red dot on a white surface.

All Colors

The same principle works for all the colors, primary, secondary, and tertiary. In this next example, using a green dot painted on the surface, we can see all the frequencies of light (illustrated by red, yellow and blue) are emitted from the full spectrum light.
Once the light hits the surface the pigment of the green paint absorbs the most all of the frequencies and only reflects the wavelengths in the green range. (between the yellow to blue frequencies)

For more information on how to mix color using the RYB subtractive color system visit the following links.

Color Wheel
Mixing using the primary colors
Muting Color