8. Color Illusions – Visual Phenomena

Colors do not always seem to be what they are. The artist mixes a hue in pigment form until it looks right on his palette or trial paper, only to find that, when applied to his painting, the effect is different. It appears duller or brighter, or even of a different hue. Perhaps it stands out too plainly, or fades disappoint­ingly into the background. Let us in­vestigate some of the reasons for all this.

Eye Fatigue: Afterimages

We know that if we glance at a brilliant illuminant, such as the sun, it excites our eyes to a marked degree. Not only are they dazed, but they develop a form of fatigue which causes us to see images of the illu­minant, even if we close our eyes or look in the opposite direction. This excitation does not immediately pass away; the images endure for some time. We call them afterimages.

Afterimages are of different kinds, or, more properly speaking, each image passes through various stages of decay before finally disappearing. If we glance momentarily at a bright incandescent light and then turn from it, or close our eyes, we can see a definite image of the light bulb. At first it seems bright; this is called a "positive" afterimage. Gradually, it changes until it looks dark, yet is still plainly visible; this is known as a negative afterimage. By opening and closing the eyes one can often change such an image from positive to negative and back at will, as long as the retinal excitation remains sufficiently strong.

It is not so commonly recognized that afterimages can be excited by comparatively mild stimuli, yet this is true. Even areas of black or white or colored pigments can cause dis­tinct (though somewhat pale and short-lived) images; these are the kind which principally affect the work of the artist. As a rule, however, mild stimulation excites only negative images, so we shall confine our investigation to them.

Exercise 54: Black and White After­images — Gaze fixedly (from a point a foot or so away) at the center of a well-lighted white disk of paper an inch or two in size, placed against a black paper background, as sug­gested by A, Figure 16. The bigger the background the better. After a half-minute, remove the disk (without shifting the eye) and you will soon see in its place its negative after­image, darker in effect than the black background. This may take a half-second to form. For a few seconds it will gain in strength, then fade away.

When you have tried this a few times, place a black disk on a field of white, as indicated at B, and fix the eye upon it for a half-minute or so. Then remove the disk. A light spot of the same size and shape will soon appear, looking whiter than the white ground; it will grow more pronounced and then fade into nothing.

Experiment with white and black disks against backgrounds of neutral gray; the afterimages will still be definite. Place your white and black disks side by side against gray; fix­ate them; remove them; two after­images, one dark and one light, will be seen simultaneously.

Figure 16

Turning to color, our prime interest, results are even more amazing. For color experiments, you can use your paints, but it is usually more conven­ient to work with colored papers.

Packets of construction paper are usually available in assortments of vivid colors wherever school or art supplies are sold. As a matter of fact, you can just as easily cut out brightly colored areas from the illus­trations and advertisements in old magazines you may have on hand, for use in the following experiments.

Figure 17

Exercise 55: Colored Afterimages — Working in rather bright, clear light, place an intense red disk (any other convenient shape will do) against a large white background, as suggested at A, Figure 17; gaze at it for 20 to 30 seconds, then remove it from the paper. You will observe, if you do not shift your gaze, that the white paper where the disk has been seems tinted with an afterimage of pale green or blue-green, complementary to the red. If you prefer, instead of moving the disk, you can merely shift your gaze after the period of fixation. You will find you can steer a circular spot of green at will about the paper as long as it endures.

Figure 18

You will perhaps note, in gazing at the red disk, a greenish fringe ap­pearing around the edges. If you move your eyes farther from the paper, you can expand this green tone to cover a much larger area. If the eye is sufficiently fatigued, a considerable portion of the white background may seem greenish if held at an increased distance from the eye. You may be conscious of this green long enough to transfer it to other objects in the room. Every­thing on which your gaze centers will, for a moment, be slightly modified by this hue, whether you realize it or not.

Figure 19

Now turn up a portion of your red disk so a shadow is cast, as sug­gested at B, Figure 17, and gaze at the disc until the afterimage border just mentioned appears; as this bor­der spreads to cover the shadow it will tinge it with green.

We often see this phenomenon (with variations) in viewing natural objects, although we are not usually aware of it. If we look at a red vase, for instance, its shadow and back­ground may seem dyed with just a suggestion of complementary green, particularly if the eye is shifted a bit. This is something to keep in mind in painting still-life subjects.

Now look at the red disk once more, studying the hue of the red itself. It will soon look less vivid than at first, seeming to grow duller right before your eyes. You can demonstrate this better if you overlap the red disk with one of black, as at A, Figure 18, and gaze at the center for a half-minute. Then, when you remove the black disk, you will discover, where it overlapped the red disk, a red area which for a few seconds will seem more intense than the one above. See B, Figure 18.

Another demonstration of interest is suggested by Figure 19. Place a strip of red paper vertically against a white background, as at A. Fixate the center of this, and then shift it to the horizontal position B, contin­uing to look at the center of the red strip. An afterimage band of com­plementary green will be seen oc­cupying the original position of the strip and, where this image crosses the strip itself to form a square, the red will appear less vivid than on the rest of the strip. The elusive phan­tom green will seem actually mixed with the red, neutralizing it.

Now for another interesting point. We have just seen that if we gaze fixedly at a color, it seems to grow slightly dull as its afterimage forms and blends with it. Contrarily, if we fatigue the eye with a color — orange, for instance, and then suddenly turn to look at its complement, blue — this complement will appear all the brighter for a moment, for, to the blue itself, the after image blue is added. This is further proof that when the eye wanders over a paint­ing (or from one painting to another) the appearance of the colors de­pends somewhat on these afterimages which are constantly being produced by retinal fatigue (unless our glance is very hasty).

Cause of Afterimages

The cause of these phenomena is not difficult to understand. We recall from Chapter I that an object which appears white does so because it has the ability to reflect a considerable portion of all the light rays which it receives, so balanced as to give the effect of absence of color. When portions of the retina are momen­tarily fatigued through the excitation set up by a distinct color, as in these recent experiments, this balance is disturbed; the tired retinal areas are temporarily incapable of receiving the sensation of white. Being in a sense blinded to the rays of one particular color, they see only the sum total of the rays of the remaining colors of which white light is composed; these form the afterimage, which obviously must be complementary to the color itself.

If we focus on a red disk, for in­stance, portions of the retina become fatigued by the red, and so, to a slight extent, blind to it. Sympathet­ically, the retina is also temporarily blind, but to a less degree, to the closely associated orange and violet. Consequently, when we remove the red disk, portions of the eye are able to see only the other colors which make up the white light — green, blue and yellow — and these merge to form the greenish afterimage. In a few seconds, the eye recovers Its sensitiveness to red and its associ­ated colors, and the afterimage disappears.

Now perform experiments, such as you have carried out with red, using other colors. You will discover that it is possible to create a comple­mentary afterimage for any hue. This fact is sometimes utilized in preparing color wheels. Although afterimages are somewhat pale, they are strong enough to make hue match­ing possible in tints and each pigment tint can then be brought to the needed intensity.

Experiment also with backgrounds other than white — particularly with black and neutral gray. You will learn that distinct images can be formed regardless of background.

Exercise 56: Adjacent, Combined Im­ages—The retina can be fatigued by more than one color at a time. Ar­range disks of the primaries — red, yellow and blue — to form a triangle against a white background, as at A, Figure 20. Then fixate these, focusing the eye at a point at the center be­tween the three circles. You will soon find that each color becomes rimmed with a tint of its complementary hue. If you remove the disks without shifting your gaze, pale second­aries — green, violet and orange — will show in disk form as afterimages, as suggested at B.

Figure 20

Such compound afterimages af­fect our vision constantly. When one views a painting, for example, he often fixes his gaze on one color after another or several colors at a time, although scarcely conscious that he does so. Then, as his gaze shifts, he transfers afterimages here and there. Obviously, in a painting they are seldom seen against white.

Exercise 57: Overlapping Combined Images — Perform a series of tests of the sort indicated in Figure 21, where a red disk is placed to overlap yellow, blue, black and white surfaces. After the necessary period of fixation, remove the disk and compare the various portions of the afterimage. Such an experiment should be enough to prove that afterimages do affect almost all color appearances.

One thing which we learn from all such experiments is that comple-mentarism is natural; that colors such as we paint opposite each other on the color wheel, though wholly unlike in appearance, are still related, and so can be advantageously employed together under many conditions, some of which will be discussed subsequently.

Other Phenomena

These remarks on retinal fatigue and its resultant afterimages cover all that the average artist needs to know about this subject, for after­images, although affecting color ap­pearances and convincing us of the relationship between colors and their complements, are such fleeting and uncontrollable things that compara­tively Little practical application can be made of them. Therefore, although we shall touch on them from time to time, we turn now to other phenom­ena of more direct application.

M. E. Chevreul, for many years the superintendent of the dyeing depart­ment of the Gobelin tapestry manu­factories, included the results of his experiments with dyes in his book, The Principles of Harmony and Contrast of Colors. In the light of later knowledge, we know that he was wrong in some of his claims. His volume has, nevertheless, formed the background for much of the discussion of color in pigment form which has followed.

Figure 21

Working under the handicap of the weaver, who cannot easily make changes in his work, Chevreul dis­covered many strange things about color. He learned, for instance, that a thread of a given color might ap­pear faded, if used in one place, yet intense in another. He learned that colors which are harmonious in some relationships are discordant in others. He learned, in short, the general truth we stated in the beginning of this chapter — that colors do not always seem to be what they are. Further, he worked out various rules or principles designed to assist the colorist in the practical employment of color. He particularly pointed to certain facts regarding what he called "simultaneous contrast" in colors.

We are all familiar with optical il­lusions of line, as when parallel straight lines appear divergent or crooked, or lines which are short are made to look longer (see Figure 22). It is not so commonly realized, how­ever, that solid areas of white, gray or black trick us as do lines. In other words, we have illusions of tone.

Figure 22. Optical Illusions

A simple illusion which we draw from physics is known as irradiation. If a bright object is seen against a dark background, it tends to look bigger than it is. If the end of an iron bar is gradually heated, for example, it seems to increase in size (beyond its actual expansion) as its temperature is raised until, when white hot, it appears to be considerably larger than the rest of the bar.

In drawing we can obtain something of this illusion. If we compare A and B, Figure 16, under bright illu­mination, the white circle of A will probably seem slightly more expan­sive than the black circle of B. The two are actually equal.

This brings us to Chevreul's fundamental Law of Simultaneous Con­trast, which tells us, in substance, that if we arrange colors — this in­cludes white, gray and black — side by side or in such manner that one is seen against a larger area of an­other, they tend to modify one another. In other words, colors are modified in appearance by their proximity to other colors.

In A, for instance, the circle looks brighter because of the black against which it is placed, and the square darker because of the adjacent white. So great is the contrast, in fact, that the white circle actually looks whiter than the rest of the page.

While we have this point before us, let us turn to Figure 23. Here the tone surrounding the white area has been softened towards the outer edges to blend gradually into the page. This causes the eye to be drawn all the more sharply to the difference between the inner circle and its surrounding black; the white circle seems whiter than white — an illusion, of course.

Another interesting illusion is shown in Figure 24, where the gray looks darker against the white than against the black, although it is the same throughout. In monochromatic drawings such illusion often develop and require adjustment. We illustrate the same point again at A and B, Figure 25; the two gray squares are exactly alike in value, whatever the eye may say. At C we show a somewhat different application of the same principle, for here each of the juxtaposed tones, though actually flat, appears through induction (if rightly viewed) to be a bit graded. Each tone seems slightly lighter or darker toward the edge than it is, through simultaneous comparison with the adjacent tone.

Exercise 58: Simultaneous Contrast, Black and White — If you perform the experiments just discussed, you will find them more convincing than the illustrations shown here. It should be clear when you have finished that even simple tones of black, white and gray are not always what they appear to be.

Colors likewise can deceive the eye. If we should tint the white circle at A, Figure 16, with color — yellow, for instance — the tint would look brighter as seen against the black than if viewed by itself on white paper. This illustrates one of Chevreul's rules that all light colors seem most striking against black. And, refer­ring again to B, Figure 16, it is not hard to understand that all dark colors seem most striking against white, for this small black circle could easily be supplemented by any dark hue with little change in general effect.

Exercise 59: Simultaneous Contrast of Colors — Now carry out the exper­iment suggested by A and B, Fig­ure 25, using small colored squares instead of gray ones. If you substi­tute green for the gray, for instance, it will appear darker on white than on black. Further, if you substitute light and dark colors for the large white and black squares, you will find that dark colors upon light colors look darker than on dark colors, and, conversely, light colors upon dark colors look lighter than on light colors. Thus, so far as values are concerned, colors appear to be quite other than what we know them to be.

Figure 23. Simultaneous Contrast

Figure 24

Figure 25

It is not only values which depend on environment, however. Place a small square of neutral gray on a blue background, and the gray will seem to take on an orange cast. The same gray against orange will show a hint of blue. This will be very evi­dent if large squares of blue and orange are placed side by side, each centered with a small square of the same gray, and with tracing paper laid over the whole.

Figure 26

As a striking test, lay small green circles in the centers of two adjacent large squares, one light yellow and the other dark blue, as in Figure 26. The green against the yellow will seem darker in value than against the blue, and slightly blue-green in hue. The green against the blue will seem slightly yellowish. Not only will the two small green areas ap­parently differ, but the yellow, con­trasted with the green and blue, may appear a bit orange, and the blue, contrasted with the yellow and green, a bit purple. Tracing paper placed over the colors will emphasize the contrast.

This test demonstrates Chevreul's argument that colors are influenced in hue by adjacent colors, each tint­ing its neighbor with its own complement. Intensities, as well as values and hues, are affected by environ­ment, as we have already seen. If two complementary colors lie side by side, each seems more intense than by itself.

Experiments with colored paper will make clear these and other interesting facts about the effects of colors on each other when they are seen in close proximity. You will learn, for instance, that dark hues on a dark ground which is not complementary will appear weaker than on one which is; that light colors on a light ground which is not complementary will seem weaker than on a complemen­tary ground; that a bright color against a dull color of the same hue will further deaden the dull color; that when a bright color is used against a dull color, the contrast will be strong­est when the latter is complemen­tary; that light colors on light grounds (not complementary) can be greatly strengthened if bounded by narrow bands of black or complementary colors; and that dark colors on dark grounds (not complementary) can be strengthened if similarly bounded by white or light colors.

These pointers serve merely as an introduction to this interesting sub­ject. The reader who cares to in­vestigate such phenomena further can find much of value in Chevreul's own book.

Remember that the laws of simul­taneous contrast do not hold unless the contrasted colors are placed in close proximity.

A Summary of Chevreul's Laws

Here is a summary of the most important of Chevreul's laws of si­multaneous contrast.

1.  Colors are modified in appearance by their proximity to other colors.

2.  All light colors seem most strik­ing against black.

3.  All dark colors seem most strik­ing against white.

4.  Dark colors upon light colors look darker than on dark colors.

5.  Light colors upon dark colors look lighter than on light colors.

6.  Colors are influenced in hue by adjacent colors, each tinting its neigh­bor with its own complement.

7.  If two complementary colors lie side by side, each seems more intense than by itself.

8.  Dark hues on a dark ground which is not complementary will ap­pear weaker than on a complementary ground.

9.  Light colors on a light ground which is not complementary will
seem weaker than on a complementary ground.

10. A bright color against a dull color of the same hue will further
deaden the dull color.

11. When a bright color is used against a dull color, the contrast
will be strongest when the latter is complementary.

12. Light colors on light grounds (not complementary) can be greatly strengthened if bounded by narrow bands of black or complementary colors.

13. Dark colors on dark grounds (not complementary) can be strength­ened if similarly bounded by white or light colors.

Color Activity

When you perform experiments like those just suggested, you will see that colors vary greatly in their affec­tive and attentive powers. Some can best be described as active, lively, restless, insistent, positive, bold, ex­panding or advancing. Others seem passive, negative, subdued, timid, submissive, reserved, contracting or retreating. Some suggest warmth, others coolness; some impress us as heavy and inert, others as light and animated. You should cultivate the habit of sizing up different colors which you see about you, noting their characteristics and your reactions to them. This will help you, when it comes to painting, to choose those colors best fitted to your mood and purpose, a matter of great importance.

Warm and Cool Colors

Some of these various character­istics of colors seem particularly sig­nificant or are sufficiently tangible to be understood easily and put to practical use. That certain colors seem warm and others cool is a fact that can be often used to advantage. Hues of the red, orange and yellow group are the ones considered warm. They suggest flame, blood and sun­shine, and are especially appropriate when bright, stimulating effects are sought. Hues analogous to blue are thought of as cool. They bring to mind cool water and ice and the sky of winter, and are at their best (there are exceptions) for purposes requir­ing restraint and subordination.

Cool colors also suggest distance or expansion and are, therefore, oft­en called "retreating" colors; warm colors, contrarily, are classed as "advancing." If we wish to paint distance or make areas seem spa­cious, we give preference to cool colors; in the foreground, or where we wish attention concentrated, we use warmer tones. As warm colors generally are associated with light, so cool colors suggest shadow, an­other fact that we apply when painting.

Of the various advancing colors, red and orange are considered to have the greatest force. Advertisers use them as a means of gaining maximum attention. The artist em­ploys them when he wishes particu­larly to emphasize a portion of his subject. Yellow has less power. It carries well and has compelling force against dark or complementary back­grounds, or if bordered or accented with darker areas, but is relatively weak if contrasted with light tints or white.

Retreating colors, although carry­ing well as dark spots, often show weakness of hue if viewed from a distance. Greens and violets stand at the half-way point between heat and cold. They contain both warm and cool colors and vary proportionally in their abilities to advance or recede. Yellow-greens and violets leaning strongly toward red tend to advance and have considerable pow­er to attract; blue-greens and blue-violets tend to recede and have little compelling force.

The carrying or attractive power of colors depends, as our experiments have indicated, not alone on hue, but also on value and intensity. A gray-red, for example, although it may attract as a dark spot, will have little force compared with the same hue unneutralized. This will be plainly evident if paper slips of these colors are placed across the room.

We have already seen that the ac­tivity of colors depends to no small extent on background. Distance, too, plays an important part in color strength. If one looks down a long city street with brick buildings on either hand, he will generally observe that the reds of the brickwork appear duller and less distinct the farther away they are, particularly if the at­mosphere is a bit hazy, a blue or purplish hue gradually taking the place, in the extreme distance, of the red. In other words, warm tones usually appear cooler in proportion to their distance from the eye. This is true of all colors to some extent.

Cool colors do not always seem to retreat, by the way; certain vivid hues, viewed near-by, appear particularly vigorous and emphatic, especially if against a complementary background. The author once noticed a bright blue automobile near at hand. Contrasted with brown and red buildings, it seemed extremely conspicuous, but as it drove away its color softened rapidly. Such popular, if unscientific, color descriptions as " hot tur­quoise, " " electric blue, " " shock green, " etc. are further evidence that in certain values and intensities even blues and greens might seem warm rather than cool, advancing rather than retreating.

Not only do colors show such ac­tivity as we have just mentioned, but they have the power also of stimu­lating a wide variety of emotional reactions — as many of us are aware. Red and orange are exciting; blue and green tend to have a calming effect. These are generalizations that most people accept without thinking. Then there are the tradition­al associations of certain colors with particular kinds of human qual­ities or emotions: passion is associ­ated with red; jealousy with green; purity with white or sometimes blue; evil with black or red. But the emotion­al interpretations of color are far from universal. Yellow, which is an accepted synonym for cowardice in the western world, for instance, is said to be a holy color in the Orient where it is worn by Buddhist monks.

Color also seems to have very personal meanings. We are all conscious, to some extent at least, of individual color preferences. Col­or consultants to industry, who have done a great deal of research on this subject, tell us that blue, which is usually listed as the most generally preferred hue, is often the choice of the individual who is rather quiet, reserved, retiring, and doesn't care to appear conspicuous. Red, on the other hand, and understandably, is more likely to be the choice of the outgoing personality who loves ex­citement and enjoys being the center of attention. Some authorities have gone much further in their attempt to see complicated psychological meanings in color preferences, but, thus far at least, their interpretations are largely speculative and of little concern to the artist, so we shall not discuss them in detail here.

What we have tried to offer here is enough to show what a complex thing color is, emphasizing the need for serious study and experimenta­tion on the part of the earnest student. Yet one can paint successfully (and many artists do) with little knowledge of the reasons behind such things as we have been discussing.

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