CHAPTER I.
THEORIES OF COLOUR.
1. Elements of Woven Pattern--2. Occurrence and Utility of Colour in Loom Productions--3. Treatment of Colour in Relation to Textiles--4. Methods of Using Colours in Textiles--5. Colour Phenomena--6. Analysis of Light--7. Utility of Prismatic Experiments--8. Schemes of Colouring--9. Primary Colours--10. Compound Colours--11. The Three Constants of Colour--12. Temperature of Colours.
1. _Elements of Woven Pattern._--Weave, compounds of form, and blending of colour are the three primary elements of textile design. They enter, either separately or in combination, into the many styles of loom effects. Weave relates specifically to the build or structure of the fabric, and is a necessary factor in any type of texture, whether plain, twilled, or ornamental in character. It is the scheme or plan of crossing the warp and weft yarns that forms or produces the fabric. Weave may give a compact texture subordinate in effect to other elements in the design; or, it may be the constructive and not the ornamental part of the pattern; yet in several woven specimens it possesses both these qualities. Fabrics of this description are not embellished with compounds of form or colour, and hence derive their design from the structural plan employed in the operation of weaving. Schemes of intertexture giving these results are devised in such a manner as to form, by interlacing warp and weft, an even fabric, decorated with a type of pattern consisting of minute effects in threads or yarns, and which may be subdued or decided in definition.
Fig. 1 is an elementary type of Weave design or Pattern. The weave used is Fig. 1A. The sections are produced thus:--
_A._ White warp crossed with white weft. _B._ Grey „ „ „ „ _C._ White „ „ black „ _D._ Grey „ „ „ „
[Illustration: FIG. 1.]
[Illustration: FIG. 1A.]
Four degrees of definition of the design are present. The textural effect is clearly visible in section _A_, but increasingly distinct in sections _B_, _C_, and _D_, due to the improved or more pronounced contrasts of the shades of warp and weft combined.
Briefly considered, Weave has the following functions in textile design:--
(1) In the construction or build of the fabric.
(2) In the development of textural design (Fig. 1).
(3) In the production of special and compound makes of fabrics.
(4) It is employed to accentuate or subdue in simple and decorative styles certain parts of the design--producing harmony of composition, whether due to blends of form, colour, or both.
Combinations of form have no relation whatever to the structural arrangement of the fabric. The sphere of form in woven design is not constructive or utilitarian, but in the amplest sense ornamental. It is surface decoration obtained by amalgamating, on definite principles, linear and curvilinear lines: ornament, consisting of geometrical or floral features, is applied to such loom products as dress, mantle, and vesting fabrics; silk textures, including neckties, handkerchiefs, robes, and decorative styles; damasks, quiltings, tapestries, etc.; carpets, hand-woven or tufted (produced on the vertical loom and now made in Donegal and some parts of Scotland as well as in the East); velvet, or cut pile (Axminster type); looped or uncut pile (Brussels type); and Kidderminster and other plain-surface productions.
Colour, the third characteristic in design, is differently related to textile effects from Weave and Form. The special function of colour is to impart brightness of tone and improve the qualities of the design. There are many varieties of pattern in fabrics for wear, which possess freshness owing to the style and method of colouring practised. In the woven decorative arts, colour may be the main constituent of the design, or employed to develop its integral parts.
2. _Occurrence and Utility of Colour in Loom Productions._--Colour is extensively used in woven design. It obtains, and is the prevailing element of the pattern, in all classes of fancy woollens, such as tweeds, flannels, and light textures, and thick figured rugs, wraps, and shawls. Whether the pattern be stripe, check, figure, or intermingled effect, it obtains its outline and detail from the method of colouring adopted. But colour is not confined to woollens; it is also an important factor in design produced in worsted, silk, cotton, jute, ramie, and other yarns. There is, in worsteds, a larger diversity of weave design than in woollen or carded-yarn textures; but, still, colour is very extensively employed to develop the effects due to weave and form, and also to impart a cheerful and lustrous appearance to the cloths. Patterns in dress fabrics, shirtings and blouses, made entirely of cotton, are frequently combinations of fancy shades; while, if the fabrics composed of silk and jute materials are considered, including--in silk--ties, handkerchiefs, and various kinds of matelasses; and--in jute--simple carpets, mats, and coarse rugs, it will be discovered that the colour element of the design largely predominates. This brief summary of the textures, in which fancy shades are used, shows that colouring, and the combinations of colours, in all branches of woven products embellished with design, are the elements which give tone and character to the styles. Though the fabrics produced may be soft to the touch, substantially made, uniform in structure, and skilfully finished, yet a lack of brightness and harmony of colouring so powerfully detracts from the merit of the pattern, that these qualities, in themselves, are not sufficient to give the fabric an attractive appearance--particulars which demonstrate the importance of choice and tasteful colouring in designs produced in the loom. Evidently colour is of twofold utility in the development of woven effects; for it may, firstly, be the sole constituent of the pattern; and, secondly, a supplementary element which affords precision and beauty to the composition of the design.
3. _Treatment of Colour in Relation to Textiles._--Though, to a considerable extent, the principles of colouring are similar in all types of decorative design--harmonious blending and contrasting combinations possessing like qualities in whatever materials they obtain--still there are several reasons why some of the recognized canons of the science of colour are inappropriate, if not inapplicable, when textiles are the media of development. Foremost of these reasons are the technical difficulties which arise in the employment of colour in woven pattern. There is not the same facility nor means for its application here, as in the treatment of ordinary surface decoration. The make of the fabric, and the principles of its structure, determine the system of distribution; while the general aspect of the entire body of colouring varies according to the nature of the materials employed. If the same colourings which appear harmonious, neatly toned, and cheerful in arrangement in a velvet pile carpet, were reproduced in a silk texture, many points of dissimilarity would be noticed in the general effect obtained, though the tint and hue of the shades combined, might be identically the same in the respective fabrics. Why is this? Are not the apparent modifications in the colourings--for such they appear when thus compared--due, first, to the difference in the nature of the materials composing the textures; second, to the dissimilitude of their structural character; and, third, to the distinct principles of weaving practised in their production? The pile of the carpet--dense and compact--gives breadth, force, and richness to the colours; whereas the fine and clear texture of the silk imparts a more precise effect to the shades, causing the whole blend to possess an aspect which, while harmonious, lacks that mellow quality of bloom so characteristic of the pile production. It is clear, therefore, that colour in textiles requires to be studied as a special art. Its functions and effects in woven fabrics are so various and distinct from what they are in ordinary decorative work, that it can only be effectively treated when the nature of textile materials, and the diverse structures of the fabrics, are considered. In a word, there are not only recognized principles of woven design which have no place in purely ornamental art, but also schemes and laws of colouring which simply apply to the development of pattern in textile fabrics. Any exposition, therefore, of the theory and practice of colouring, to be useful to the textile technologist, must be given in relation to the varied technicalities of the weaver’s craft.
4. _Methods of Using Colours in Textiles._--Colour is not always applied to woven textures on the same system. The method of utilization depends upon the composition of the design to be woven, and on the structure of the cloth it is intended to produce. There are fabrics in which the colour element is so decided that the effect obtained is somewhat similar to the results noticed in ordinary surface decoration. Take, for example, silk textures of a ribbon class, in which, by skilful workmanship and exact sketching, any floral form may be developed with a delicacy of toning and correctness of delineation that cannot be improved upon, even though the crayon or the brush should be employed. But this is not a common, because not a useful, species of designing and colouring. Carpets and tapestry fabrics illustrate other principles of employing fancy shades. The structure of some types of carpets very materially affects the character of the colourings. In Brussels and tapestry, for instance, the loop or pile of the carpet which forms its distinguishing feature, prevents that solidity and compactness of colouring noticeable in the silk ribbon or dress material. If the same design and blend of shades introduced into a Kidderminster or Scotch carpet were subsequently applied to a Brussels production, they would be entirely changed in appearance; for there is no common principle of intertexture in the respective carpets. In cotton, silk, woollen, and worsted textures, colour is found to have a different tone or cast in each fabric. Fancy colours in cottons, while decidedly smart and clear in effect, are comparatively non-lustrous, raw, and dull in toning.[1] Silk is distinguishable by brilliance of hue; woollen colourings have a unique depth and saturation of hue characteristic of the material employed in their manufacture; while worsted colourings are bright, definite, and smart in appearance.
These differences are due to the physical formation and properties of the several fibres and yarns. Thus, a filament of silk is almost transparent, and shines like a smooth glass rod when light falls upon it; that of wool is solid and opaque in the centre, but its exterior consists of a multitude of semi-transparent scales, which, when of large dimensions and uniformly arranged--as in the best qualities of Lincoln and Leicester wools--reflect light with a minimum amount of dispersion, and impart to the woven material a lustrous aspect. Cotton has no such partially transparent surface. Its downy structure absorbs light freely, while what is reflected is so broken up, that the colour resultant is impoverished in saturation and brightness. To clearly apprehend the degree to which the nature of the raw material is capable of changing the tone or character of colours, compare three plain woven textures of the same colour made of silk, wool, and cotton respectively. Lustre, brilliance, and richness are the features of the silk colouring. Though thus bright, it lacks that fulness and depth of hue which appertains to the wool production, the filaments of which closely compounded, and all tinted alike, possess a peculiar bloom and saturation of colouring not to be found either in the silk or cotton. The cotton texture is somewhat dull and flat in quality of hue, lacking the brightness of silk. Such is the importance of the relation of the material to the species of coloured effect produced in textiles, that it will require subsequent analysis.
The various methods of employing fancy shades in patterns obtained in the loom may be briefly summarized as follows:--
TABLE I.
METHODS OF APPLYING COLOUR TO TEXTILES.
I. In mixture cloths, for suitings, coatings, and costumes.
_a._ By combining or blending various colours of materials. _b._ By combining several classes of twist threads.
II. In plain, twilled, mat, and fancy weave designs, for trouserings, coatings, suitings, dresses, costumes, flannels, shirtings, and fine textures.
_a._ By applying colour to the warp, forming stripes. _b._ By applying colour to the weft, producing spotted patterns. _c._ By applying colour to both warp and weft, giving checks and other styles.
III. In figured designs for dresses, mantlings, vestings, shawls, rugs, mauds, carpets, and tapestries.
_a._ By using one or several series of extra warp yarns. _b._ By using one or several series of extra weft yarns. _c._ By using one or several series of extra yarns in both warp and weft.
Each of these systems is capable of further subdivision; but, as here given, they represent the principles of colouring the general classes of woven designs.
5. _Colour Phenomena._--Under ordinary conditions, light is essential to colour apprehension. Diversity of hue may be made evident to the mind by mechanical agitation of the optic nerves in a darkened room. Of course, such an experiment is only useful as showing the media by which colour sensations are rendered visible, or rather conveyed to the mind.
The colour of an object is determined by three things: the nature of light, the physical properties of the material on which light falls, and the power of the observer’s eye. These are obvious conditions. Change the light from brilliant daylight to gaslight, and a richly coloured fabric undergoes several modifications--the hues suffer in brightness and lose a measure of their co-relative value. Or, by using a mono-chromatic light (that from burning sodium is a compound of two yellow lights of similar quality in the spectrum[2]), coloured objects may be changed to a similar hue. That colour is affected by the nature of the material has been stated in reference to fibres of wool, cotton, and silk.
[Illustration: FIG. 2.]
Incapacity to correctly distinguish the hues, tones, and tints of colour is caused by some affection of the retina. Training and practice in the matching and blending of colours may enhance the acuteness of colour vision. The Gobelin tapestry-weaver will select, without hesitancy, from a bundle of bobbins of tints of material of the same hue or colour, the one he requires. Similarly, the carpet-weavers of Donegal--after a period of training--will unerringly manipulate a varied assortment of delicate colours.
“Light is due to waves--or other periodic disturbances, whose recurrence resembles that of waves--in the ether of space; and just as air-waves of a certain definite frequency of recurrence will induce in the ear the sensation of a sound of a particular pitch, so will the impact of ‘ether-waves’ of a certain particular frequency induce in the eye a sensation of light of a particular colour.”[3]
The extreme visible red in the spectrum is produced by 392 billions, and the extreme visible violet by 757 billions of waves per second. The table gives the wave frequency of the spectral colours:--
TABLE II.
WAVE FREQUENCY OF THE SPECTRAL COLOURS.
Red 492·4 billions per second. Orange red 484·1 „ „ Orange 503·3 „ „ Orange yellow 511·2 „ „ Yellow 517·5 „ „ Green 570 „ „ Blue 591·4 „ „ Cyan blue 606 „ „ Blue 635·2 „ „ Violet blue 685·8 „ „ Puce violet 740·5 „ „
As the frequency of the vibrations increases, or as they are diminished in length, the visible colours of the spectrum are produced. Just as the pitch of a musical instrument depends upon the celerity of the wave it produces, so the colour of an object is subjective to the length of the undulations transmitted. This analogy between the phenomena of sound and light has led some colourists to attempt a scheme of colours based upon similar laws to musical harmony.[4]
6. _Analysis of Light._--When a pencil of sunlight passes through a prism horizontally fixed, as in Fig. 2, it is decomposed, and produces on the screen the colour spectrum _A_, Plate I. In the intervals between each hue there is a gradation to which the colours are severally susceptive. Red passes, through a diversity of tinting, into orange, which graduates into yellow; and green, green blue, blue, indigo, and violet occur in succession, all softly toning into each other. The purity and intensity of each colour will be observed.
[Illustration: FIG. 3.]
A second and useful experiment may be made as follows:--Place a piece of black cardboard, about an inch wide and a few inches in length, on a white ground, and view it through the edge of a prism. If this experiment be correctly made, a result will be obtained corresponding to _B_, Plate I. The edge nearest the observer produces the violet, blue, and green side of the spectrum, while the opposite edge gives red, orange, yellow, and pale yellow--these two series of spectrum colours of distinct qualities being divided by a narrow band of black. Coldness is the distinguishing characteristic of the violet side, and warmness that of the red side; in the upper portion of the spectrum are found the intense, ostentatious hues, while in the lower portion are the colours of a subdued, soft quality. Yellow and green are beautifully toned. The former passes from a yellowish orange into a pure, bright tint, which is softly shaded off into white. Green, on the front edge of the black line, is similarly graduated in hue, but as the band of this colour is not so broad as the yellow strip, its shadings are not so extensive; still, it imperceptibly changes from deep into pale green, and diminishes in intensity until it disappears in white light. One feature of this experiment will at once be observed, namely, the brilliance and richness of coloured lights, when compared with corresponding colours obtained by pigments or dye substances. Bloom, depth, and purity of hue characterize the former; but however the latter are produced, they seem, in comparison, to be lacking in fulness, intensity, and brightness.[5]
[Illustration: Plate I A = SPECTRUM B = SPECTRUM RESULTANT FROM VIEWING A STRIP OF BLACK ON A WHITE SURFACE THROUGH A PRISM]
7. _Utility of Prismatic Experiments._--Experiments with the prism afford suggestive exercises in colour blending. Seeing that the results of these experiments are richer by far than those obtained by pigments, and always harmonious in tone, they are calculated to enhance appreciation for pure and lustrous colouring. For the purpose of successful manipulation of prismatic experiments, and of viewing in a suitable manner the effects that may, by this means, be produced, a piece of black velvet or cloth should be employed, and patterns cut out of white cardboard placed on it, and then the design thus arranged examined through the prism. The more ingenuity exercised in pattern origination, the more pleasing the combinations resultant. Fig. 3 illustrates the class of designs adapted for this work. Form and arrangement should be of the most elementary kind, and the whole pattern clear and pronounced, in order to allow of a complete development of the colours formed on the respective edges of the various figures. Intermingled, diminutive patterns give confused and indistinct effects. On the other hand, broad and large designs yield lustrous colourings, which the experimenter may feasibly dissect, and which teach principles in colour arrangement, harmony, and contrast, of utility in pattern production.
When the pattern in Fig. 3 is viewed through the refractory angle of a prism at a distance of about two feet, and about three times larger than here sketched, it forms an interesting assortment of colourings and tinted effects. Any description of this experiment, however concise and clear, can only afford a vague idea of the real appearance of the pattern when prismatically examined. Still, to assist the reader to make the experiment accurately himself, a detailed analysis is given. Treating of the different sections of the patterns, the edge of band A, nearest the observer, should be considered first, which commences with pure green, running through blue, purple, deep violet, and crimson. The crimson results from the violet rays of this edge blending with the intense red rays of the further edge of band _A_.
SMALL LINES _B_ AND _C_. The former begins with crimson, which successively changes into scarlet, orange, and yellow, a small strip of white separating these colours from those of band _C_, which consists of various tints of green and orange.
DIAMOND FIGURES OF BAND _A_. The front edges of these are tinted with scarlet, orange, and yellow, and the opposite edges with various shades of green.
CIRCLES OF BAND _D_. First, as to the edges nearest the observer. These are coloured with emerald-green and grass-green. It will be noticed that the green in this section of the pattern is distinct from that produced by the front edge of band _A_, being, as stated, more grass- than sea-green. Its peculiar tint results from the orange rays of the upper edge of band _C_ intermingling with the green rays of the circles. As the centres of the circles are approached, green is succeeded by blue, purple, and black. Second, as to the distant edges of the circles. At these points red, crimson, scarlet, and orange--the latter colour graduating imperceptibly into yellow--all occur. It is notable that the yellow hue is somewhat dingy, being adulterated with other colours. Compare it, for example, with the yellow resulting from the extreme edge of this diagram. Its dulness and impurity are due to certain colours intermingling with it. Thus, the space between the extreme edge of the circles and band _E_ is so limited, that the yellow rays of the circular objects combine with the green rays of the latter, and, as a consequence, the yellow suffers in purity and luminosity.
BANDS _E_, _F_,AND THE FRONT EDGE OF _G_. These, very closely resembling strips _B_, _C_, and _A_, require no description.
EXTREME EDGE OF BAND _C_. Here the red side of the spectrum is seen in its intensity and lustre; it begins with deep red, which gradually verges into orange, and the latter into yellow.
This simple experiment demonstrates the value of prismatic results. All colourists should study shade combinations through these media. Analysis of the colourings obtained in this manner increases the acuteness of the faculty of discrimination of the brilliance and depth of hue of individual colours. Though, in practice, the textile designer has to deal exclusively with pigments and dye substances, yet the intensity and beauty of the combinations resulting from the decomposition of light are so novel and suggestive, that all desirous of cultivating aptitude for harmonious colourings will be at pains to multiply experiments of this class, which afford a true conception of what constitutes harmony and contrast in colours.
That such compounds of spectrum colours have an application to textile design is evident from the specimens on Plate II., in which tints of the pure or prismatic colours are used in silk fabrics. The mode of distribution is irregular, but this is done for the purpose of subduing the strength of contrast which would be formed if the colours were used on the basis of the experiment described. Two fabrics are given as examples on Plate II. No. 1, a silk ribbon, is produced by weaving in a bold warp rep or cord weave, the colours being arranged in the warp to give the intermingled shaded effect. The weft is a thick, yellow cotton yarn, but, owing to the weave structure, does not show on either the face or underside of the texture. In the second example, No. 2, the colouring is due to printing the warp prior to weaving. It has a similar intermingled composition, but the colour contrasts are harsher in tone. Both examples show the utility of prismatic colours in their purity, or when slightly subdued by tinting.
[Illustration: FIG. 4.]
8. _Schemes of Colouring._--There are two important theories of colour--the Light Theory and the Pigment Theory. The former deals with the phenomena of colours, the attributes of light, and the laws, which control the modification of the intensity, hue, and tone of colours. These varied phenomena are theoretically of value, but as they have few practical applications, the pigment theory of colouring is necessarily adopted in the applied arts, and deals with colour as an active element in decorative design. Every possible shade and hue of colour may be obtained by mixing red, yellow, and blue in variable proportions, and, of course, by toning and tinting with white and black. Mixtures of lights and pigments, however, do not give analogous results. Lambert[6] is credited with being the first to discover and prove that the colours due to these two causes were rarely identical, and frequently widely dissimilar. His method of doing this consisted in using two coloured wafers, _A_ and _B_ (Fig. 4), which were placed on a black surface, and a piece of ordinary glass, _g_, fixed vertically. It was found that when blue and yellow were thus simultaneously seen, the rays reflected by them did not, when co-mingled, give green, but a whitish-coloured sensation. This fact was also subsequently elaborated by Helmholtz, who pushed his inquiries into the spectrum itself, and, by blending the lights, obtained valuable results. Blue-green, when mixed with red, instead of giving a brownish or greenish grey, as with pigments, was found, like ultramarine blue and yellow, to also constitute white light. With pigments, a mixture of chrome yellow and ultramarine blue, in variable quantities, forms different tints of green. Microscopic examination of this compound does not reveal the separate particles of yellow and blue pigments, but simply the greenish hue. The real and obvious distinction between spectrum and pigment combinations is that the former are additions, while the latter are subtractions. Knowing this, it will at once be evident that the colours obtained by these two methods cannot coincide.
The following are some of the results of combining coloured lights and pigments respectively:--
TABLE III.
COMPOUNDS OF COLOURED LIGHTS.
Red + green = yellow. Should the green be slightly bluish = white. 2 red + green = orange. Green + blue = sea-green. 2 green + blue = greenish sea-green. Blue + red = purple. 2 blue + red = violet. Red + green + blue = white. 2 red + green + blue = white + red, or pale red. 2 red + 2 green + blue = white + yellow, or pale yellow. Red + 2 green + 2 blue = white + sea-green, or pale sea-green. 2 red + green + 2 blue = white + purple, or pale purple.
TABLE IV.
COLOURS RESULTING FROM COMBINING PIGMENTS.
Primaries. Secondaries. Tertiaries. Red + yellow = orange. 2 R + Y + B, or O + P = russet. Yellow + blue = green. 2 Y + R + B, or O + G = citron or greenish olive. Blue + red = purple. 2 B + R + Y, or G + P = olive.
9. _Primary Colours._--Writers on the pigment theory are all agreed as to the selection of the simple colours; but scientists have, in treating of this subject, chosen several sets of hues as primaries. Young and Helmholtz take red, green, and violet; vermilion, emerald-green, and ultramarine blue are selected by Maxwell. When the subject of colour is considered with a view to its practical application to the arts, it is needful to base all combinations on the scheme elucidated by Chevreul, Hey, Field, and others--that red, blue, and yellow (Plate III., Nos. 1, 2, and 3) are primary colours, and all others the resultants of mixing them in variable quantities. For technical purposes, it is therefore only feasible to deal with colour as it changes, according to the pigments combined; hence red, yellow, and blue will be regarded as primaries, because, when mixed with each other and with black and white, every possible shade of colour may be obtained.
10. _Compound Colours._--These are of two classes--secondaries and tertiaries. The secondaries--green, orange, and purple (Plate III., Nos. 4, 5, and 6)--are composed of two primaries, while the tertiaries--russet, citron, and olive (Plate III., Nos. 7, 8, and 9)--are composed of two secondaries. Orange and purple produce russet or reddish brown; orange and green produce citron or greenish olive; and green and purple, olive. On reducing these shades to their simple elements, it is found that they are each composed of three primaries, with one predominating and giving tone to the colour. Russet, for instance, contains a double portion of red, for red is a constituent of both the orange and purple which enter into its composition; citron contains a double portion of yellow, and olive a double portion of blue.
The hue or tone of a compound colour is determined by the proportionate quantities of the primaries combined in its production. For example, to procure a bluish green, blue must be the predominating and yellow the subordinate colour; while, on the other hand, to obtain a yellowish green, yellow would be the predominating and blue the subordinate colour. Reddish or yellowish orange is got by increasing the red or yellow constituents of this colour; and bluish or reddish purple, by increasing the blue or red components of this secondary. This affords some idea of how colours are modified and multiplied. Taking the three secondaries and subjecting them to similar treatment, a diversity of shades will be found to result. Russet (Plate III., No. 7) is composed of two parts red, one part yellow, and one part blue. It will be obvious that by varying these proportions another series of hues will result. By increasing the red constituent, the warmth of the colour is intensified; by increasing the yellow, the reddish tone is neutralized; while an increase of the blue would add to its depth and saturation. Similar results are obtained by modifying the constituents of the other primaries. Thus citron--composed of two parts yellow, one part blue, and one part red--may be changed to a yellowish, bluish, or brownish citron, according to the quantity of yellow, blue, or red used. Olive, which consists of two parts blue, one part red, and one part yellow, varies from a deep olive-green, brownish olive, to a yellowish olive-green, as the blue, red, and yellow constituents are increased.
[Illustration: Plate II
SPECTRAL COLOURING OF FABRICS 1. Woven-design Specimen 2. Printed-yarn „ ]
The tertiary shades are the most useful colours employed in textile design. They are generally used for the ground of the fabric, while the secondaries and primaries are utilized in enhancing the brightness of the pattern.
11. _The Three Constants of Colour._--The three constants of colour are, _purity_, _luminosity_, and _hue_. If a piece of paper is painted vermilion and placed across the red end of the spectrum, it will be seen to be deficient in purity. Emerald-green and ultramarine blue papers, when compared with their respective sections of the spectrum, are found to be similarly defective. By mixing white light with the colours of the spectrum they may be so adulterated as to correspond with, or match, those obtained by the use of pigments. Artificial colours are never perfectly pure--they always contain some measure of foreign element, which can only be correctly determined by bringing them in contact with the colours of the spectrum. The second constant, _Luminosity_ or _Intensity_, depends on the degree of light a colour reflects. Yellow, orange, and red represent the most luminous, and green, blue, and violet the least luminous end of the spectrum. It will be evident that it is possible to have two or more colours of the same degree of purity, but of different degrees of brightness. Two scarlets might both contain the same proportionate quantities of colour and of white light, and yet be dissimilar, simply on account of one being more intense in hue than the other. To match the two colours, the more luminous one would require to be exposed to a dull light, or the less luminous to a bright light. The third constant, _Hue_, is that special property which is caused by a definite refrangibility of light, producing the colour proper. Green and red may be exactly of the same purity and brightness, but they are different in hue, each being produced by a distinct refrangibility of rays.
12. _Temperature of Colours._--The temperature of the spectrum colours is not uniform. It augments from violet to red. Herschel, by exposing thermometers to the several tints of the solar spectrum, determined the temperature of each colour, and proved that, proceeding from the most refracted or violet end of the spectrum to the least refracted or red end, there is a successive increase of heat. Besides luminous rays, the sun emits a mass of invisible but potent calorific rays. Herschel, pushing his thermometers beyond the visible red and violet rays, discovered the presence in the spectrum of ultra red rays of intense heat, and ultra violet rays of a less heat. The solar spectrum may therefore be described as consisting of three distinct sections: First, of the ultra and invisible red rays; second, of the luminous rays, red, orange, yellow, green, blue, and violet; and third, of the ultra and invisible violet rays. Though it is thus evident that each spectral colour has a different temperature, yet it cannot be assumed on this basis that a red fabric will possess a greater degree of heat than a blue fabric composed of the same materials; because all rays penetrating a coloured body are not luminous, and yet, whether luminous or non-luminous, they possess properties of heat. Were the rays absorbed by a coloured surface only luminous, then it would be possible, by estimating the measure of absorption, to determine the colour temperature. But the bulk of radiation from any luminous body consists of invisible calorific rays, regarding which colour teaches absolutely nothing. A fact that has to be taken into consideration is, that a body may be highly susceptible to one class of rays, but insusceptible to other classes. As it is generally known that black garments are more effective retainers of solar heat than white garments, it may be pointed out why this is the case. White clothes absorb the invisible rays, but reflect the luminous rays which constitute solar light. Black or dark clothes, on the other hand, not only retain the dark rays which penetrate them, but also the visible rays; and hence they are that degree warmer than white fabrics of the same structure and material, as the difference in the influx of temperature due to the absorption of luminous as well as invisible rays. Tyndall explains that if a white cloth were spread over the snow, it would even act as a shield to the latter instead of assisting it to thaw. Snow, which is ice in a powdered form, absorbs the dark rays with greater avidity than a white fabric; and, as both the particles of snow and the threads of the texture reflect the luminous rays poured upon them, the snow would melt sooner without the cloth than with it. Indeed it would be found that in a short time the cloth would occupy quite a prominence--the snow not covered by it thawing more rapidly than that over which it is spread. Should a black fabric of similar material be next placed on sunned snow, it would produce the very opposite results. Absorbing the luminous as well as the dark rays, it retains more of the sun’s heat than the snow, which rapidly melts under it; while the surrounding and uncovered snow remains comparatively unthawed and icy. Both the white texture and the snow are powerless as regards the luminous rays emitted by the sun; the myriads of fibres composing the former receive no warmth from them, nor can the ice-like atoms of the latter be melted by them. They, in a word, can only be changed by the dark rays. As to the black-surfaced texture, there are different conditions to be taken into account. It is both an absorbent of the invisible and of the luminous rays, consequently dark materials not only attract but retain more of the sun’s heat than light materials. More than this cannot be stated with certainty about the warmth-yielding qualities of woven textures of various colours.
FOOTNOTES:
[1] Mercerized cottons possess some of the qualities of silk colourings.
[2] “Colour”: _Chambers’ Encyclopædia_.
[3] Abney’s _Colour Measurement and Mixture_.
[4] Wilkinson’s _Harmonious Colouring_.
[5] Paterson’s _Science of Colour Mixing_.
[6] Atkinson’s _Ganot’s Physics_; Tyndall’s _Fragments of Science_.