Polychromy

“ The sun's own light shows under this method of spectroscopic analysis millions of tints, in fact I might say millions of red tints, and so forth, right through the spectral list of colours. But also many thousands of tints are wanting. Imagine a rainbow-coloured ribbon, the colours ranged along its length, so that the ribbon is black at both ends, and that from the black of one end the colour merges into very deep red, and thence by insensible gradations through orange, yellow, green, blue, indigo, and violet, into the black of the other end. ”

“ As said above, it is exposed under a positive cliché, plans, designs, etc., drawn on tracing paper or linen. The more transparent the material, the more rapid the chemical changes. During the insolation—and it is very short—the chromic compound is reduced, the parts corresponding to the ground, that is, the transparent parts of the cliché, are discolored, while those under the design remain unaltered; the image being, therefore, faintly visible, and being formed of the chromic mixture, it is developed by the fumes of aniline in a blue black tone. ”

“ The test for a chrome is tinting strength, taking care to make a comparison with the same grade of colours, that is, light, medium or orange chrome. Fineness is another important test. Placing a small quantity on glass and passing a palette knife over it and pressing firmly will detect grit if present. In the lighter chromes it is well to look for the greyness of tone which is objectionable. Chromes mix well with white lead and are strong in body.
Ochres. —Analysis is of no value in determining the value of an ochre. Sometimes chrome yellow is used to tone it up. ”

“ If we examine under the microscope a pure unproofed fur fibre, its characteristic structure is quite visible. Examination of an unproofed fibre dyed with logwood black shows again the same characteristic structure with the dye inside the fibre, colouring it a beautiful bluish-grey tint, the inner cellular markings being black. A proofed fur fibre, on the other hand, when examined under the microscope, is seen to be covered with a [Pg 65] kind of translucent glaze, which completely envelops it, and prevents the beautiful markings showing the scaly structure of the fibre from being seen. ”

“ In water it is white, but without lustre. In the primary atoms of both it is perpetual; in their products, not so. In earth it is variable; and seven colours are distinguished: viz. white, yellow, green, red, black, tawny (or orange) and variegated. The varieties of these seven colours are many, unenumerated. The six simple colours occur in the atoms of the earth; and the seven, including variegated, in its double atoms, and more complex forms. The colour of integrant parts is the cause of colour in the integral substance. ”

“ Let us see if we can now change our chrome yellow to chrome orange, just as we did in the glass vessel by boiling in lime-water. I place the yellow fabric in boiling lime-water, when it is coloured or dyed orange. In each little tubular cotton fibre the same change goes on as went on in the glass vessel, and as the tube or glass vessel looks orange, so does the fabric, because the cotton fibres or tubes are filled with the orange chromium compound. You see this is quite a different process of pigment colouring [Pg 84] from that of rubbing or working a colour mechanically on to the fibre. ”

“ But if, whilst the liquid is evaporating, it is kept in motion by stirring with a thin glass rod, the crystals form separately, each rhombic prism having its angles well defined, and giving beautiful colours with the polarized light. Again, pyro-gallic acid, when allowed to flow evenly over the slide in a saturated solution, covers the surface in long “needles,” which are richly coloured by polarized light; but if any small portion of dust or other matter should form a nucleus around which these “needles” may gather, the beauty is wonderfully increased. ”

“ Science describes chroma as the purity of one wave length separated from all others. Other wave lengths, INTERMINGLING, make its chroma less pure. A beam of daylight can combine all wave lengths in such balance as to give the sensation of whiteness, because no single wave is in excess.8
(24) The color sphere (see Fig. 1) is a convenient model to illustrate these three qualities,—hue, value, and chroma,—and unite them by measured scales.
(25) The north pole of the color sphere is white, and the south pole black. Value or luminosity of colors ranges between these two extremes. ”

“ So many crystals are transparent, and so clear and limpid, that it was evident to the earliest observers that they were at least as homogeneous throughout as glass, and yet that at the same time they must be endowed with an internal structure the nature of which is the cause of both the exterior geometric regularity of form, so different from the irregular shape of a lump of glass, and of the peculiar effect on the rays of light which are transmitted through them. ”

“ Thus the red rays are least refracted, and the violet the most, and the yellow, green and blue are intermediate between them, being placed in the order [Pg 22] of least refrangibility. Between these there is of course every shade of simple colour, one melting into the other. In order to form a pure and bright spectrum with prisms, in a room of limited dimensions, we have to use certain auxiliary apparatus which are not positively essential, though convenient. The real essentials to form a spectrum are a narrow slit, a glass prism, with perfectly plane faces, and a lens. ”

“ Owing to the limitations of pigment-material, however, it is impossible to reproduce the intensities of the Spectrum satisfactorily. An approximation is all that we can achieve in painting.
THE SPECTRUM SEQUENCE AND
THE CIRCUIT OF THE COLORS 135. Having produced the scale of twelve colors in the values of their greatest intensities, and as intense as possible, we get an approximation to the Spectrum with this difference, that the color Violet-Red (Purple) which we get in pigments and mixtures of pigments does not occur in the Spectrum and, so far as we know, does not belong in the Spectrum. ”

“ These crystals must be placed at the end of the reflectors, and when they transmit polarized light, their brilliant colours and forms will vary by turning the cell which contains them, or by giving a motion of rotation to the analyser. Thin films, or laminæ of selenite of different thicknesses, and generally of such a thickness as gives the bright rings of the second order of colours in Newton’s scale, may be placed in a narrow cell or object-box, and may have their outlines of various curvatures, so as to combine both form and colour in the Kaleidoscopic figure. ”

“ When all the colour-producing rays are reflected in due proportion, the colour of the object is white; when all are absorbed the colour is black. If blue rays only are absorbed the resulting colour is orange-red; and generally, whatever colour an object appears to us, it is because the complementary colours are absorbed by it. The reason why rays of only certain refrangibilities are reflected, and the rest of the incident light absorbed by each substance, is supposed to depend upon the molecular structure of the body. ”

“ In all these instances it is clear, from the experiments themselves, as well as from other experiments which form no part of our present subject, that the modifications which light undergoes are due to the internal structure of the crystals used. And it becomes a question of interest whether it be not possible, by some mechanical process, performed upon a non-cystalline substance, such as glass, so far to imitate a crystalline structure as to reproduce some of the optical results already shown. ”

“ Unless introduced and guaranteed by houses of acknowledged reputation, newly discovered pigments are to be used with caution. Good colours have ever been prized with so true an estimation of their value, that to produce such, after so many ages of research is no ordinary accomplishment. But too many resplendent pigments, fruits of the fecundity of modern chemistry, have been found deficient. The yellow and orange chromates of lead, for instance, withstanding as they do the action of the sunbeam, become by time, foul air, and the influence of other pigments, inferior to the ochres. ”

“ A fruitful source of disillusionment lies in the fact that the plates are sensitive to the light to a degree so different from our eyes. As the blue and violet rays chiefly act upon them, they cannot render the real effects of colouring. It is greatly to be desired that we should manage to perfect orthochromatic plates, sensitive to green, yellow and red rays of light. I myself have been unable to secure 673 674 675 good results with orthochromatic plates with the telephoto lens, as I have found them always too little sensitive to white light for instantaneous work. ”

“ His theory of colour stops short at the beginning—it is without its learning. The sentiments of colours are in their mixtures, their relative combinations, and appropriate applications, and we venture to suggest to other Polychromatists, besides Mr Owen Jones, that the grammar of colouring, if learned properly, will lead to a mystery which the blue, red, and yellow, of themselves the A, B, C of the art, are quite insufficient to teach. The study is by none more required than our painters in glass ”

“ From the negatives obtained positives are. made of carbon tissue (bichromated gelatin pigment paper) . The carbon tissue, perhaps better, pigment tissue, used with the red light negative is charged with an inalterable blue pigment, the blue being the complementary of the red used in the production of the negative. The pigment tissue for the red and yellow positives, that is, the tissue used with the green and violet-light negatives is charged with the complementary inalterable red and yellow pigments. ”

“ How is it that the combination of three colours suffices to form white, or to match any colours we wish, be they spectrum colours to which a little white is added, or the colours of pigments? The most plausible theory that can be advanced is that it is only necessary for the eye to be furnished with a three-colour-perceiving apparatus to give the impression of every colour, and yet this would be somewhat difficult to believe had we not had the experiments narrated in that chapter before us. ”

“ To determine the hue of a pigment from the analysis of the light it reflects is a problem in physiological optics, the solution of which varies with the character of the observer's eye. The three primary color-curves of the eye must be determined, and the total intensity of each wave-length of the spectrum of the pigment must be divided in the proportions indicated by the color-curves into three components—red, green, and violet. ”

“ If we receive a prismatic spectrum on some papers, we have evidence that the molecular or chemical disturbance bears some relation to the color of each ray, or, in other words, that colored light so modifies the action of ENERGIA that the impression it makes is in proportion to the color of the light it accompanies, and hence there results a molecular arrangement capable of reflecting colors differently. ”

“ If too much of one colour appears, it must be toned down till the grey is formed. This is a very simple piece of apparatus, and for experiments with pigments will be found to be very handy. When the right tint of each is secured in this manner, a further test may be made by making the pigmented surfaces into sectors, and rotating them together, when if the double-image prism gives correct results, the angular aperture of the sectors should be 180° each, to match a grey produced by a mixture by rotation of black and white. ”

“ Bodiless colors, which give a complete solution [65] with water will run into each other on being thrown on the size and will flow from the paper when it is lifted off. The insolubility of the color bodies therefore prevents them from running although they are disarranged on the size in drawing and although one color may be compressed or expanded by a second, yet they all remain separate without mixing, except, perhaps, that the shade of the first color becomes more intense, because its color particles are pushed together by the more violent expansion of the second color. ”

“ From this standpoint these cells are true chromatophores. In an eye exposed to the light the pigment-granules occupy distal positions in these cells; in one in the dark they come to lie in proximal positions. The place occupied by the pigment in a given eye is entirely determined by the presence or absence of light in that eye, for the two eyes have no sympathetic relations. Moreover if a persistent shadow is cast on part of one eye, the condition characteristic for the dark is assumed by that part even though the pigment in the rest of the eye is in the position characteristic for light. ”

“ Some of those changes are produced even by day if the colours of the scale are viewed through a green crystal, and others if they are viewed through yellow or azure crystals. Artificial light is without doubt differently constituted from that of the sun: it contains probably a scanty mixture of red rays with an abundance of the yellow, green, and azure. ”

“ The construction of the polype seems then to be confined to these glandular grains, to the viscous matter, and the invisible fibres which act upon the glareous substance.
The structure of the arms of the polypes is very analogous to that of their body. When they are examined by the microscope, either in a contracted or dilated state, their surface is shagreened; if the arm be much contracted, it appears more so than the body ”