Additive Color

White light is a mixture of all wavelengths of the visible spectrum. We can select three individual color lights from the visible spectrum that in combination or by themselves will produce the complete range of colors including white. These three specific colors of light are red, blue, and green.

Any two colored lights may be mixed on a white substrate to produce a third distinct color. Incident primary red and blue lights produce the color magenta (Figure 5.15). Similarly, superimposed beams of primary blue and green produce cyan (blue-green). Superimposed beams of primary blue, green, and red will produce white light. This production of white light is just the reverse of the production of a spectral array resulting from white light incident on a prism. In Figure 5.16 the region occupied by all three beams is white (W). The region oc-

Incident Incident

White Substrate

Fig. 5.15. The color magenta (purple) is produced by the addition of red and blue light incident on a white substrate.

White Substrate

Fig. 5.15. The color magenta (purple) is produced by the addition of red and blue light incident on a white substrate.

Fig. 5.16. The colors blue (B), cyan (C), green (G), yellow (Y), red (R), magenta (M), and white (W) are produced by the addition of beams of blue, green, and red light incident on a white substrate. This shows that white can be produced by the additive mixtures of these three pure colors, referred to as additive primaries.

Fig. 5.16. The colors blue (B), cyan (C), green (G), yellow (Y), red (R), magenta (M), and white (W) are produced by the addition of beams of blue, green, and red light incident on a white substrate. This shows that white can be produced by the additive mixtures of these three pure colors, referred to as additive primaries.

Green

Fig. 5.17. The color triangle with the primary additive colors (blue, green, and red) at the corners and the secondary additive colors (cyan, yellow, and magenta (purple)) at the edges.

Blue Magenta Red

Fig. 5.17. The color triangle with the primary additive colors (blue, green, and red) at the corners and the secondary additive colors (cyan, yellow, and magenta (purple)) at the edges.

cupied by overlapping beams of red and green is yellow (Y); of green and blue is cyan (C); and of red and blue is magenta (M). Another representation of these relations is given as a color triangle in Figure 5.17. Red, blue, and green are primary additive colors. The addition of these three colors produces white, represented by the open circle in the center of the triangle. Cyan, yellow, and magenta, also in a triangular relationship and represented by the dashed line, are secondary additive colors.

5.5 Subtractive Color

Fig. 5.18. Subtractive color is illustrated by white light incident on a translucent cyan layer (red absorbed), on a translucent yellow layer (blue absorbed); and then the remaining (nonab-sorbed) green light is reflected from the white substrate.

Just as additive color mixing refers to the process of adding colored lights, the sub-

tractive process refers to the removal of certain wavelengths of light as a result of absorption. This is the condition when we observe light reflected from objects. It is the mixing of subtractive primary colors that determines the observed colors in painting media.

Subtractive color mixing can be illustrated by illuminating with white light superimposed layers of translucent color on an opaque white substrate. In Figure 5.18 a layer of translucent cyan is superimposed over a layer of translucent yellow. As the incident white light passes through the cyan layer, red wavelengths are absorbed. Blue wavelengths are absorbed in the passage through the yellow layer. The light reflected from the white substrate is green. This is an example of how painters are able to mix colors through the use of translucent glazes.

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