Part the First — The Laws of Contrast of Colour by M. E. Chevreul

Part the First

Section the First Of the Law of Simultaneous Contrast of Colours, and of Its Demonstration by Means of Experiment

Chapter I

Manner of observing the Phenomena of the Simultaneous Contrast of Colours.—Definition of Simultaneous Contrast.

The twofold phenomena of contrast of colour and contrast of tone may be readily shown by the following.

Experimental Demonstration of Contrast of Tone.

Upon looking at the four half-sheets for a few seconds, it will be seen that A contiguous to B will be lighter than Aʹ, while B will seem darker than Bʹ.

Upon looking at the cardboard, it will be seen that the strips, instead of presenting flat tints, will each appear of a tone diminishing in intensity from the edge a a to the edge b b. In the stripe 1, the contrast is produced simply by the contiguity of the edge b b with the edge a a of the stripe 2; in the stripe 10, it is simply by the contiguity of the edge a a with the edge b b of the stripe 9. But in each of the intermediate stripes 2, 3, 4, 5, 6, 7, 8, 9, the contrast is produced by a double cause; partly by the contiguity of the edge a a with the edge b b of the stripe which precedes it, partly by the contiguity of the edge b b with the edge a a of the darker tint which follows it. The first cause tends to raise the tone of the half of the intermediate stripe; while the second cause tends to lower the tone of the other half of the same stripe.

In consequence of this contrast, the stripes seen from a proper distance, resemble channels rather than flat surfaces. For, in the stripes 2 and 3 for instance, the grey is weakened from the edge a a to the edge b b, presenting to the eye the same effect as if the light fell upon a channelled surface; there is however this difference, that in the real channelling the enlightened part would throw a reflection upon the dark portion.

12. Contrast of tone occurs with colours so called as well as with grey; thus to repeat the experiment (9), fig. 1, with the halves o o of a sheet of paper of a light tint of a certain colour, and the two halves p p of a sheet of paper of a darker tint of the same colour, it will be seen that o contiguous to p will be lighter than oʹ, and p darker than pʹ. In short, it may be demonstrated as has been done (10) that the modification of colours in juxtaposition becomes weaker in proportion to their distance from the line of contact; and in order to observe this effect in bodies which are not contiguous, it is only necessary to experiment as described in (10).

The colours experimented upon must be as nearly as possible of equal intensity.

13. Experimental Demonstration of Contrast of Colour.—If we arrange as before, the two halves of an unglazed coloured sheet of paper, and two halves of another sheet of a different colour, but as nearly as possible of equal intensity, or rather of tone (8), upon looking at the four half-sheets o oʹ, p pʹ for a few seconds, we shall see that o differs from oʹ and p from pʹ; consequently the two half-sheets, o p, seem to undergo a reciprocal modification of tint, which is rendered apparent by comparing their colours with those of oʹ and pʹ.

14. No 1.	Red	inclines to	Violet.
14. No 1.	Orange	″	Yellow.
2.	Red	″	Violet.
2.	Yellow	″	Green.
3.	Red	″	Yellow.
3.	Blue	″	Green.
4.	Red	″	Yellow.
4.	Indigo	″	Blue.
5.	Red	″	Yellow.
5.	Violet	″	Indigo.
6.	Orange	″	Red.
6.	Yellow	″	Bright Green.
7.	Orange	″	Bright Red.
7.	Green	″	Blue.
8.	Orange	″	Yellow.
8.	Indigo	″	Blue.
9.	Orange	″	Yellow.
9.	Violet	″	Indigo.
10.	Yellow	″	Bright Orange.
10.	Green	″	Blue.
11.	Yellow	″	Orange.
11.	Blue	″	Indigo.
12.	Green	″	Yellow.
12.	Blue	″	Indigo.
13.	Green	″	Yellow.
13.	Indigo	″	Violet.
14.	Green	″	Yellow.
14.	Violet	″	Red.
15.	Blue	″	Green.
15.	Indigo	″	Deep Violet.
16.	Blue	″	Green.
16.	Violet	″	Red.
17.	Indigo	″	Blue.
17.	Violet	″	Red.

Chapter II

The Law of the Simultaneous Contrast of Colours,
and the Formula which represents it.

16. After I had assured myself that the preceding phenomena were constant for my sight when it was not fatigued, and that many persons, accustomed to judge of colours, saw them as I did, I sought to reduce them to an expression sufficiently general to render it possible to predicate the effect which would be produced upon the organ of vision by the juxtaposition of two given colours. All the phenomena that I have observed seem to depend upon a very simple law, which in its most general sense may be enunciated in these terms: When two contiguous colours are seen at the same time, they appear as dissimilar as possible, both with regard to their optical composition and their depth of tone. Therefore there may be at once simultaneous contrast of colour, properly so called, and simultaneous contrast of tone.

17. Now two colours in juxtaposition, o and p, will differ from each other in the greatest possible degree when the complementary of o is added to p, and the complementary of p is added to o; indeed by the juxtaposition of o and p, the rays of the colour p, which o reflects when it is seen alone, and which are active in that case, cease to be so when o and p are in juxtaposition. Now under these circumstances, each of the two colours, losing what it has analogous to the other, must be so much more different from it.

Let us represent—

The colour of the stripe	O	by the colour	a plus white B,
””	P	″	aʹ plus white Bʹ,
the complementary colour of a by C,
””	aʹ	″	cʹ,

the colours of the two stripes seen separately are—

Colour of O = a + B; colour of P = aʹ + Bʹ;

by juxtaposition they become—

Colour of	O =	a + B + cʹ,
	P =	aʹ + Bʹ + c.

We will now show that this expression amounts to taking away the rays of aʹ from the colour a of O (15), and to taking away the rays of the colour a from aʹ of P.

For let us suppose—

B reduced into two portions, white = b + white = (aʹ + cʹ),

Bʹ reduced into two portions, white = bʹ + white = (a + c).

The colours of the two stripes seen separately are—

The Colour of	O =	a + b + aʹ + cʹ,	and the colour of
	P =	aʹ + bʹ + a + c.

By juxtaposition they become—

The colour of	O =	a + b + cʹ,	and the colour of
	P =	aʹ + bʹ + c.

An expression which is evidently the same as the former, except for the values of B and Bʹ.

19. I have said that simultaneous contrast may at the same time affect the optical composition of colours, and the depth of their tone; consequently, when colours are not of the same depth, that which is deep appears deeper, and that which is light appears lighter; that is to say, the former appears to lose white light, while the latter seems to reflect more of it. Thus there may be, in looking at two contiguous colours, simultaneous contrast of colours and simultaneous contrast of tone.

Chapter III

The Law of Simultaneous Contrast of Colours demonstrated by the Juxtaposition of a certain Number of Coloured Bodies.

20. Let us now apply the above formula to the seventeen observations of Chapter I., and we shall see that the modifications of contiguous colours are precisely those which would result from the addition to each of them of the complementary of the contiguous colour (18). The rank these colours occupy in Chapter I. may be readily noted, as I have attached to each the number applied to it in that chapter. And for the complementary of each colour see (6). (See Plate II.)

Orange and Green, 7.
21.	Orange,	the complementary of	Blue,	being added to	Green,	makes it	Bluer	or less	Yellow.
	Green	””	Red	″	Orange	″	Redder	″	Yellow.
Orange and Indigo, 8.
22.	Orange,	the complementary of	Blue,	being added to	Indigo,	makes it	Bluer	or less	Red.
	Green	””	Red	″	Orange	″	Redder	″	Yellow.
Orange and Violet, 9.
23.	Orange,	the complementary of	Blue,	being added to	Violet,	makes it	Blue	or less	Red.
	Violet	””	Orange-yellow	″	Orange,	″	Yellower	″	Red.
Green and Indigo, 13.
24.	Green,	the complementary of	Red,	being added to	Indigo,	makes it	Redder	or more	Violet.
	Indigo	””	Orange-yellow	″	Green	″	Yellow.
Green and Violet, 14.
25.	Green,	the complementary of	Red,	being added to	Violet,	makes it	Redder
	Violet	””	Green-yellow	″	Green	″	Yellower.
Orange and Red, 1.
26.	Orange,	the complementary of	Blue,	being added to	Red,	makes it	Violet	or	Crimson.
	Red	””	Green	″	Orange	″	Yellower.
Violet and Red, 5.
27.	Violet,	the complementary of	Green-yellow,	being added to	Red,	makes it	Orange-yellow.
	Red	””	Green	″	Violet	″	Indigo.
Indigo and Red, 4.
28.	Indigo,	the complementary of	Orange-yellow,	being added to	Red,	makes it	Orange.
	Red	””	Green	″	Indigo	″	Blue.
Orange and Yellow, 6.
29.	Orange,	the complementary of	Blue,	being added to	Yellow,	makes it	Greener.
	Yellow	””	Indigo	″	Orange	″	Redder.
Green and Yellow, 10.
30.	Green,	the complementary of	Red,	being added to	Yellow,	makes it	Orange.
	Yellow	””	Indigo-violet	″	Green	″	Blue.
Green and Blue, 12.
31.	Green,	the complementary of	Red,	being added to	Blue,	makes it	Indigo.
	Blue	””	Orange	″	Green	″	Yellower.
Violet and Blue, 16.
32.	Violet,	the complementary of	Greenish-yellow,	being added to	Blue,	makes it	Greenish.
	Blue	””	Orange	″	Violet	″	Redder.
Indigo and Blue, 15.
33.	Indigo,	the complementary of	Orange-yellow,	being added to	Blue,	makes it	Green.
	Blue	””	Orange	″	Indigo	″	Violet.
Red and Yellow, 2.
34.	Red,	the complementary of	Green,	being added to	Yellow,	makes it	Green.
	Yellow	””	Indigo-violet	″	Red	″	Violet.
Red and Blue, 3.
35.	Red,	the complementary of	Green,	being added to	Blue,	makes it	Green.
	Blue	””	Orange	″	Red	″	Orange.
Yellow and Blue, 11.
36.	Orange-yellow,	the complementary of	Indigo-violet,	being added to	Blue,	makes it	Indigo.
	Blue	””	Orange	″	Yellow	″	Orange.
Indigo and Violet, 17.
37.	Indigo,	the complementary of	Orange-yellow,	being added to	Violet,	makes it	Red.
	Violet	””	Greenish-yellow	″	Indigo	″	Bluer.

38. It is evident that, all other things being equal, the modifications of contiguous colours will be so much the more marked, as the complementary colour C or Cʹ, which is added to each of them, differs more from them; for the complementary Cʹ which is added to the colour O, is identical with it, as the complementary C is identical with the colour P to which it is added; and the modifications of O and P will simply augment the intensity of their colours. But are there yet any two bodies known which present to the observer two pure colours perfectly complementary to each other? Certainly not; all those which are coloured by reflection reflect (7), besides white light, a great number of rays of various colours. We cannot instance a red body and a green body, or an orange and a blue, or an orange-yellow and an indigo, or a greenish-yellow and a violet, which reflect pure or mixed colours, absolutely complementary to each other. So that the juxtaposition of these colours produces only a simple augmentation of their intensity. Hence, although it is less easy to verify the law of contrast with respect to red and green, or orange and blue, &c., than with respect to those which are the object of the seventeen experiments just described (15), yet, upon applying it to the former, it will be seen that their colours acquire a most remarkable brilliancy, strength, and purity. This result, perfectly conformable to the law, may be easily understood: for example, an orange-coloured object reflects blue rays, as a blue object reflects orange rays (7). Hence, when a blue stripe is put in contact with an orange stripe, although it is admitted that the first appears to the eye to receive blue from the orange of the second, as this appears to receive orange from the blue of the blue stripe; or what is the same thing, that the blue stripe appears to destroy the effect of the blue rays of the second stripe, as these appear to destroy the effect of the orange rays of the blue stripe—it is evident that the two colours so contrasted must purify each other, and become more intense. But the blue may incline to green or violet, and the orange to yellow or red; that is to say, the modification may not only affect the intensity of the colour, but also its physical composition. However, if this latter effect take place, it is always much more feeble than the first. Besides, if you look several times at the same coloured stripes, you will see that the blue which at first had appeared to you greenish will afterwards appear inclining to violet; and that the orange, which had appeared at first yellowish, will incline to red; so that the phenomena of modification, as it affects the physical composition of colour, will not have the constancy of those which are the subject of the preceding seventeen observations (15). I now proceed to state the observations I have made on colours which are most nearly complementary to each other.

Red and Green.

39. Red,1 the complementary of Green, placed by the side of Green, increases its intensity.

Green, the complementary of Red, placed by the side
of Red, increases its intensity.

Such is the theoretical result, the experimental result entirely agrees with it. When we place a green, inclining more to yellow than to blue, side by side with, 1st, a slightly orange-red, 2nd, a slightly crimson-red, and 3rd, an intermediate red, and repeat our observations several times on each of these assemblages of colour, we shall observe different results; that is to say, in one case the red will appear more orange and the green yellower, and in another the red will appear more violet and the green bluer. We shall find also that the change may be attributed as much to a difference in the intensity of the light upon the colours as to fatigue of the eye.

When we place a green, inclining rather to blue than to yellow, side by side with, 1st, a slightly orange-red, 2nd, a slightly crimson-red, and 3rd, an intermediate red, the results are the same as with the first green, but with this difference,—that in the assemblage of bluish-green and of slightly crimson-red, observed several times, the green and the red appear almost constantly yellower than they are separately. A result very easily understood.

Orange and Blue.

40. Blue, the complementary of Orange, placed by the side of Orange, increases its intensity.

Orange, the complementary of Blue, placed by the
side of Blue, increases its intensity.

Upon repeating these observations with a deep blue and an orange which is not too red, the two colours appear commonly to become redder.

Orange-Yellow and Indigo.

41. Orange-yellow, the complementary of Indigo, placed by the side of Indigo, increases its intensity.

Indigo, the complementary of Orange-yellow, placed
by the side of Orange-yellow, increases its intensity.

Greenish-Yellow and Violet.

42. Greenish-yellow, the complementary of Violet, placed by the side of Violet, increases its intensity.

Violet, the complementary of Greenish-yellow, placed by the side of Greenish-yellow, increases its intensity.

The result of observation is almost always in conformity with this law.

43. According to the law of the simultaneous contrast of colours, and the insensible gradation of modification, beginning at the contiguous edges of the colours in juxtaposition (11), we may show, by means of coloured circular spaces, the modifications which the principal colours induce in those which are contiguous to them.

Place wafers, circular pieces of paper, or any other convenient material about an inch and a half in diameter, coloured red, green, orange, blue, greenish-yellow, violet, indigo, and orange-yellow, each separately upon a sheet of white paper; then tint the white paper around the circle with its complementary colour, gradually softening it off from the coloured circle, when it will be found that

The Red circle tends to colour the surrounding space
	with its complementary	Green.
Green	””	Red.
Orange	””	Blue.
Blue	””	Orange.
Greenish-yellow	””	Violet.
Violet	””	Greenish-yellow.
Indigo	””	Orange-yellow.
Orange-yellow	””	Indigo.

These figures are designed to exhibit the effects of contrast to those persons who, not having studied physical laws, are, notwithstanding, desirous of understanding these effects.

Chapter IV

On the Juxtaposition of Coloured Surfaces with White.

44. When white bodies are viewed simultaneously with coloured bodies contiguous to them, they are sensibly modified. I confess that the modification is too feeble to be determined with absolute certainty while we are ignorant of the law of contrast; but, understanding that, and knowing the modifications that white undergoes in connexion with certain colours, we shall not fail to recognise this modification in special cases, provided the colours opposed to the white be not too deep.

Red and White.

45. Green, complementary to Red, being added to White, the Red appears more brilliant and deeper.

Orange and White.

46. Blue, complementary to Orange, being added to White, the Orange appears more brilliant and deeper.

Greenish-Yellow and White.

47. Violet, complementary to Greenish-yellow, being added to White, the Yellow appears more brilliant and deeper.

Green and White.

48. Red, complementary to Green, being added to White, the Green appears more brilliant and deeper.

Blue and White.

49. Orange, complementary to Blue, being added to White, the Blue appears more brilliant and deeper.

Indigo and White.

50. Yellowish-orange, complementary to Indigo, being added to White, the Indigo appears more brilliant and deeper.

Violet and White.

51. Yellowish-green, complementary to Violet, being added to White, the Violet appears more brilliant and deeper.

Black and White.

52. Black and white, which may be considered in some respects complementary to each other, become, conformably to the law of contrast of tone, more different than when seen separately. This results from the effect of the white light, which is reflected by the black (4), being more or less destroyed by the light of the white stripe. By an analogous action, the white heightens the tone of the colours to which it is contiguous.

Chapter V

On the Juxtaposition of Coloured Bodies with Black.

(See Plate 9, Page 54.)

53. A black surface being deeper than that which is contiguous to it, the contrast of tone tends to deepen it still more, while it tends to lower the tone of the contiguous colour; as on the other hand white, placed in juxtaposition with it, would heighten it. So much for contrast of tone.

54. Black surfaces reflect a small quantity of white light (4), and this falling upon the retina simultaneously with the coloured light of a contiguous body, it is evident that the black surface must appear tinted with the complementary of the coloured light; but it will be a weak tint, since it is displayed upon a ground which has but a feeble power of reflecting light. So much for the contrast of colour.

55. The lowering of the tone of the colour contiguous to the black is constantly observed; but a very remarkable fact is the weakening of the black itself, when the contiguous colour is deep, and of a nature to give a luminous complementary, as orange, orange-yellow, greenish-yellow, &c.

Red and Black.

56. Green (the complementary of Red), when placed by the side of Black, makes it appear Reddish. The Red looks clearer, partaking less of Orange.

Orange and Black.

57. A Blue (the complementary of Orange), when placed by the side of Black, causes it to appear less brilliant, or somewhat rusty, while Orange by the side of Black appears more brilliant in colour.

Greenish-Yellow and Black.

58. Greenish-yellow (the complementary of Violet), when placed by the side of Black, gives it a Violet tint, whilst the Greenish-yellow becomes clearer and more Green; but there are some kinds of Yellow which are weakened by the side of Black.

Green and Black.

59. Red (the complementary of Green), when placed by the side of Black, causes the Black to appear more Violet or Reddish; whilst Green by the side of Black becomes slightly Yellower.

Blue and Black.

60. Orange (the complementary of Blue), when placed by the side of Black, causes it to appear brighter, while the Blue becomes clearer and somewhat Greener.

Indigo and Black.

61. Orange-yellow (the complementary of Indigo), placed by the side of Black, causes it to look much brighter. The Indigo also appears brighter.

Violet and Black.

62. Violet (the complementary of Greenish-yellow), when placed by the side of Black, lightens it up; whilst the Violet becomes more brilliant and clear, and somewhat Reddish.

Chapter VI

On the Juxtaposition of Coloured Bodies with Grey.

(See Plate 10, Page 58.)

63. As the brilliancy of the light reflected by white bodies is one of the principal causes which render the sight insensible to the modifications produced in white by the juxtaposition of coloured bodies; and, on the other hand, as the feeble light reflected from black bodies is unfavourable to our perception of the modifications which they sustain from the proximity of coloured bodies, especially when the complementary of the colour of these bodies is but slightly luminous, it may be conceived that grey bodies, judiciously selected with regard to their depth of tone, would, by contiguity to coloured bodies, exhibit the phenomena of contrast of colour in a more striking manner than either black or white bodies would.

Red and Grey.

64. Grey appears Greenish by receiving the influence of its complementary Red.

The Red appears purer, less Orange perhaps.

Orange and Grey.

65. Grey appears Bluer by receiving the influence of its complementary Orange.

The Orange appears purer, more brilliant, Yellower perhaps.

Yellow and Grey.

66. Grey appears to incline to Violet by receiving the influence of its complementary Yellow.

The Yellow appears more brilliant, and yet less Green.

Green and Grey.

67. Grey appears to incline to Red by receiving the influence of its complementary Green.

The Green appears more brilliant, Yellower perhaps.

Blue and Grey.

68. Grey appears to incline to Orange by receiving the influence of its complementary Blue.

The Blue appears more brilliant, Greener perhaps.

Indigo and Grey.

69. Grey appears to incline to Orange by receiving the influence of its complementary Blue.

The Blue appears more brilliant, Greener perhaps.

Violet and Grey.

70. Grey appears Yellowish by receiving the influence of its complementary Violet.

Violet appears fresher, less dull.

70a. The grey, which was the subject of the above experiments, was as free as possible from every colouring matter foreign to black; it belonged to the scale of normal black (see Part II., 164)—that is to say, it resulted from a mixture of the purest possible black and white materials. By juxtaposition with white, it appeared deeper, and the white appeared more pure; while by juxtaposition with black, it appeared lighter and more rusty, and the black appeared deeper.

70b. One result of the complementaries of colours in juxtaposition with grey being more perceptible than when these colours are juxtaposed with white or black, is, that if instead of a normal grey, we juxtapose a grey, tinted either with red, orange, yellow, &c., these tints will be greatly heightened by the complementaries added to them. For example, a bluish grey will receive a very perceptible increase of blue from its proximity to orange, and a yellowish-grey will take a perceptible green tint from the same proximity.

Note.—The chemical nature of coloured substances has no influence upon the phenomena of simultaneous contrast.

71. The chemical nature of coloured bodies in juxtaposition has no influence upon the modifications of their colours. Whatever may happen to be the chemical composition of the coloured bodies, provided they be identical to the sight, they yield the same results. I need only cite the following examples:—Indigo, Prussian blue, cobalt, ultramarine, as nearly alike as possible, gave the same sort of modification; orange prepared from red lead, annotto, or a mixture of woad and madder, caused the same modification of the colours to which they were adjacent.

Chapter VII

On the Juxtaposition of Coloured Bodies belonging
to the Colours of the same Group of Coloured Rays.

72. Whenever there is a great difference between two contiguous colours, the difference becomes still more appreciable by putting the same colour successively in juxtaposition with the various colours belonging to the same group. For example, orange and red.

Orange being placed beside scarlet-red, pure red and crimson-red, it will be seen that the red acquires a purple and the orange a yellow tint.

Violet being placed beside scarlet-red, pure red and crimson-red, gives analogous results: the violet always appears bluer, and the red yellower or less purple.

73. These observations explain why we obtain results in accordance with the formula, even when such coloured substances are used as are far from exhibiting pure colours, namely, stained papers or stuffs.

74. The juxtaposition of coloured stripes is a means of demonstrating the difficulty of determining the types of pure colours by common pigments; at least, if we do not take into consideration the law of simultaneous contrast. For instance—

1. Place red in contact with orange-red; the first will appear purple and the second yellower, as above; but if the first red be placed beside purplish-red, the latter will appear bluish, and the former more yellow or orange; so that the same red will be purple in one case and orange in the other

2. Place yellow beside orange-yellow, the former will appear greenish and the latter redder; but if you put the first yellow beside a greenish-yellow, the last will appear greener, and the yellow more orange; so that the same yellow will incline to green in one case, and to orange in the other.

3. Place blue beside greenish-blue, the former will incline to violet, and the second will appear yellower. Put the same blue beside a violet-blue, the former will incline to green, and the second will appear redder; so that the same blue will be violet in one case and greenish in the other.

75. Hence we see that the colours which painters term simple—red, yellow, and blue—pass insensibly by juxtaposition into the condition of compound colours, since the same red is purple or orange; the same yellow is orange or green; and the same blue is green or violet.

Chapter VIII

On the Application of the Law of Contrast to the Hypothesis that Red, Yellow, and Blue are the only Primary Colours; and that Orange, Green, Indigo, and Violet are Secondary or Composite Colours.

76. The experiments to which I have just applied the principle of the modification which colours undergo by juxtaposition, and the explanation consequent upon the manner in which white light has been considered, are also clearly explained in the language of painters and dyers, who admit of only three primary colours—red, yellow, and blue. As there are persons who, while they hold this opinion, desire, notwithstanding, to give a reason for the phenomena resulting from the juxtaposition of colours, I will explain them in accordance with this language; and, for greater clearness, I make five groups of juxtaposed colours, beginning with those which include the observations to which the preceding law is most easily applied. I shall presume that orange is composed of red and yellow, green of yellow and blue, indigo and violet of red and blue.

First Group.—Two Secondary Colours having a Simple Colour as a Common Element.

It is very easy to verify the law when we look at two colours which form part of the group: we see that by their reciprocal influence they lose more or less of the colour which is common to them. It is evident that they become more unlike each other in proportion to this loss.

1. Orange and Green.—These colours having the element yellow in common, lose it by juxtaposition. The orange appears redder, and the green bluer.

2. Orange and Indigo.—These colours having the element red in common, lose it by juxtaposition. The orange appears yellower, and the indigo greener.

3. Orange and Violet.—Like the preceding.

4. Green and Indigo.—These colours having the element blue in common, lose it by juxtaposition. The orange appears yellower, and the indigo bluer.

5. Green and Violet.—Like the preceding.

Second Group.—A Compound Colour, and a Simple Colour, which is found in the Compound.

1. Orange and Red.—The orange loses red, and appears yellower; the red becomes bluer, to differ as much as possible from the orange.

2. Violet and Red.—The violet loses red, and appears bluer; the red becomes yellower, to differ as much as possible from the violet.

3. Indigo and Red.—Like the preceding.

4. Orange and Yellow.—The orange loses yellow, and appears redder; the yellow becomes bluer, to differ as much as possible from the orange.

5. Green and Yellow.—The green loses yellow, and appears bluer; the yellow becomes redder, to differ more from the green.

6. Green and Blue.—The green loses blue, and appears yellower; the blue becomes redder, to differ as much as possible from the green.

7 Violet and Blue.—The violet loses blue, and appears redder; the blue must become yellower to differ as much as possible from the violet.

8. Indigo and Blue.—Like the two preceding.

Third Group.—Two Simple Colours. (See 6, 7.)

1. Red and Yellow.—Red in losing yellow appears bluer; and the yellow losing red appears bluer; or, in other words, the red inclines to purple, and the yellow to green.

2. Red and Blue.—The red in losing blue appears yellower; and the blue losing red appears yellower; or, in other words, the red inclines to orange, and the blue to green.

3. Yellow and Blue.—The yellow in losing blue appears redder; and the blue losing yellow appears more violet; or, in other words, the yellow inclines to orange, and the blue to violet.

Fourth Group.—Two Compound Colours consisting of the same Simple Colours.

Indigo and Violet.—As indigo differs from violet only in containing more blue in proportion to red, it follows that the difference will be greatest when the indigo loses red and inclines to greenish blue, while the violet, by gaining red, inclines toward that colour. It is clear that, if the violet lost red, or if the indigo acquired it, the two colours would approximate; but, as they differ from each other, the first effect ensues.

We may further explain the preceding phenomena by considering indigo relatively to violet, as blue; then it will lose its blue, which is common to both colours, and incline to green; while the violet, also losing its blue, will appear redder.

Fifth Group.—A Compound Colour, and a Simple Colour, which is not found in the Compound.

1. Orange and Blue. 2. Green and Orange. 3. Violet and Greenish Yellow.

Upon the hypothesis that orange, green, and violet are compound colours, and that red, blue, and yellow are simple, it follows that in opposing them in the order in which they are reciprocally complementary, and supposing also that the colours so juxtaposed are entirely free from any foreign colour, there appears no reason for the compound colour losing one of its elements rather than another, or for the simple colour being unlike one of the elementary colours rather than another. For instance, in the juxtaposition of green and red, we see no reason why green should pass into blue rather than into yellow, or why the red should incline to blue rather than to yellow.

Section II

ON THE DISTINCTION BETWEEN SIMULTANEOUS, SUCCESSIVE, AND MIXED CONTRAST OF COLOURS, AND ON THE CONNEXION BETWEEN THE EXPERIMENTS MADE BY THE AUTHOR, AND THOSE PREVIOUSLY MADE BY OTHER OBSERVERS. DISTINCTION BETWEEN SIMULTANEOUS, SUCCESSIVE, AND MIXED CONTRAST OF COLOURS.

77. Before speaking of the relation of my experiments to those made by others on the contrast of colours, we must distinguish three classes of contrast. The first includes those relating to the contrast which I term simultaneous; the second to that which I term successive; and the third to that which I term mixed.

78. Simultaneous contrast of colours includes that phenomena of modification which objects variously coloured seem to undergo in physical composition, and in the depth of tone of their respective colours, when seen at the same time.

79. Successive contrast of colours includes the phenomena observed when the eyes having looked for some time at one or more coloured objects, perceive, after having ceased to look at them, images of those objects, presenting the colour complementary to that of the actual object.

80. This distinction also facilitates the understanding of the phenomena which maybe called mixed contrast; for, the retina having seen a certain colour for some time, has an aptitude to see for a further time the complementary of that colour, as well as any new colour presented by an external object; the sensation perceived being the result of this new colour, and the complementary of the first.

For want of this distinction, one of the branches of optics most fertile in applications, has not been treated with the clearness and precision which are necessary to show its importance to those who have not experimented upon it.

81. The following is a simple mode of observing mixed contrast:—Having closed one eye, the right for example, look steadily with the left at a sheet of paper of a colour A; when this colour seems to become dull, look immediately at a sheet of paper of the colour B, the eye then has the impression produced by the mixture of this colour B with the complementary (C) of the colour A.

82. To be convinced of this mixed sensation, it is only necessary to shut the left eye, and to look at the colour B with the right eye; when the sensation perceived is not only that of the colour B, but it may appear modified in the contrary way to that of the mixed sensation C + B, or what is the same, it appears to be rather A + B.

83. Upon shutting the right eye, and looking again at the colour B with the left eye, and that many times in succession, different sensations are successively perceived, but more and more feebly, until at length the left eye returns to its normal state.

84. I advise any person who thinks that one of his eyes is more able to perceive colours than the other, to look at a sheet of paper alternately with the right and left eye; if the sensations of each are identical, he may conclude that he has deceived himself. And even if the sensations be different, the experiment should be repeated several times, successively, for the difference observed in a single experiment might be occasioned by one of the eyes having been previously modified or fatigued.

85. This practice appears to me especially useful to painters. I now give some examples of mixed contrast.

86. The left eye, having looked for some time at red, has an aptitude to see afterwards green, the complementary of red. If then it be attracted by yellow, it perceives a sensation resulting from the mixture of green and yellow. The left eye being shut, and the right eye, which has not been modified by the sight of red, being opened, it sees yellow, and it is possible that this yellow may appear more orange than it is really.

87.	If the left eye had first seen	and had afterwards seen	the latter would have seemed
	Yellow	Red	Violet.
88.	Red	Blue	Greenish.
89.	Blue	Red	Orange-red.
90.	Yellow	Blue	Blue-violet.
91.	Blue	Yellow	Orange-yellow.
92.	Red	Orange	Yellow.
93.	Orange	Red	Red-violet.
94.	Red	Violet	Deep blue.
95.	Violet	Red	Orange-red.
96.	Yellow	Orange	Red.
97.	Orange	Yellow	Greenish-yellow.
98.	Yellow	Green	Bluish-green.
99.	Green	Yellow	Orange-yellow.
100.	Blue	Green	Yellow-green.
101.	Green	Blue	Blue-violet.
102.	Blue	Violet	Reddish-violet.
103.	Violet	Blue	Greenish-blue.
104.	Orange	Green	Bluish-green.
105.	Green	Orange	Reddish-orange.
106.	Orange	Violet	Bluish-violet.
107.	Violet	Orange	Yellowish-orange.
108.	Green	Violet	Red-violet.
109.	Violet	Green	Yellow-green.
110.	Red	Green	Bluer.
111.	Green	Red	Tinted-violet.
112.	Yellow	Violet	A little bluer.
113.	Violet	Yellow	Greenish.
114.	Blue	Orange	Yellower.
115.	Orange	Blue	More violet.

116. I should observe that all these colours, at least to my eyes, did not undergo equally intense or equally continuous modifications. For instance, the modification produced by the successive view of yellow and violet, or of violet and yellow, is stronger and more durable than that produced by the successive view of blue and orange, and still more than that of orange and blue. The modification produced by the successive view of red and green, of green and red, is but slight, and not enduring.

I may also add that the depth of tone exercises some influence on the modification; for, if after looking at orange, we look at dark-blue, the latter will appear greenish rather than violet, a result contrary to that afforded by a light blue.

117. I have thought it the more necessary to mention under a special name the phenomenon which I call mixed contrast, as it explains certain facts remarked by dealers in coloured fabrics, as well as the inconvenience felt by painters, who, wishing to produce an exact imitation of their models, look at them so long as to be unable to perceive their tones and modifications. I will mention two facts which have been communicated to me by manufacturers, referring the reader to Part II. for the application of the study of mixed contrast to painting.

118. First Fact. When a purchaser has looked a long time at a yellow cloth, and he is then shown an orange, orange-red, or scarlet one, he finds it dull, and judges it to be a dark or crimson-red; because the retina affected by the yellow has a tendency to see violet; and hence all the yellow of the orange colour disappears, and the eye sees it as a red, or a red inclining to violet.

119. Second Fact. If there be presented to a purchaser, one after another, fourteen pieces of a red fabric, he judges the six or seven last pieces to be less beautiful than the first, although they may be all identical. What is the reason of this false judgment? It is, that the eyes which have seen six or eight red pieces in succession, are in the same condition as if they had looked steadily for the same length of time at a single red stuff,—having a tendency to see the complementary of red, that is green. This tendency necessarily enfeebles the brilliancy of the red of the last pieces. The dealer, therefore, that he may not be a sufferer from the fatigued eyes of his customer, after showing him a few red pieces, should present some green ones, to restore the eyes to their normal state. If the view of the green were sufficiently prolonged to pass the normal state, the eyes would acquire a tendency to see red, and then the pieces seen last would appear more beautiful than the rest.

Notes

8 If we look at the same time at two stripes of unequal tints of the same colour, or at two stripes of equal tints of different colours, in juxtaposition, that is to say, contiguous by one of their edges, the eye will perceive, if the stripes be not too wide, certain modifications; in the first case affecting the intensity of the two tints, in the second, the optical composition of the two colours so placed. Now as these modifications cause the colours to appear, when looked at together, more different than they really are, I have given to them the name of the simultaneous contrast of colours. The modification which affects the intensity of colour, I term contrast of tone; and the modification which affects the optical composition of the contiguous colours, I term contrast of colour.

9 Let the two halves of a sheet of unglazed paper, about twenty inches square, be coloured clear grey, by a mixture of chalk and black; fix them, in any way, upon a piece of unbleached linen, placed across a window, at the distance of twelve inches asunder. Take two halves of another piece of similar paper B Bʹ, but of a darker grey, and coloured with the same substances. Fix A next to B and place Bʹ twelve inches from B. (See Fig. 1.)

10 It is easy to demonstrate that the modification is not equally intense over the whole of the surfaces A Aʹ and B Bʹ, but that it becomes gradually feebler from the line of contact. This may be proved by placing a card, so cut, that O and P may each present three grey stripes, as shown in Fig. 2, Plate 1. The stripes 1 1 are more modified than the stripes 2 2, and these are more so than the stripes 3 3. However, in order that this modification may be effected, it is not absolutely necessary that O and P should touch; for if the stripes 1 1 be covered, the stripes 2 2, 3 3 will be modified.

11 The following experiment, which is simply the result of the two preceding (9 and 10), is well suited to demonstrate the extent of contrast of tone. Upon a sheet of cardboard divided into ten stripes, each about a quarter of an inch broad, lay a uniform tint of Indian ink. As soon as it is dry, lay a second tint on all the stripes except the first. As soon as the second is dry, lay a third on all the stripes except the first and second, and so on of all the rest, so as to have ten flat tints, gradually increasing in depth from the first to the last. (See Fig. 3.) If ten strips of paper of the same grey, but each of a different tone, be laid upon a cardboard, in the preceding gradation, it will serve the same purpose.

15 It thus appears from the experiments described in this chapter that two coloured surfaces in juxtaposition, viewed simultaneously, present to the eye two modifications—one relative to the depth of tone of their respective colours, and the other relative to the physical composition of those colours.

18 The following formulæ will illustrate this:—

← Back to The Laws of Contrast of Colour