Monochrome

“ And this over-sensitiveness and fastidious objection to strong contrast, this love for the externals of technique, raising brushwork to a higher pedestal than the idea, has much to do with the exclusiveness of modern painting and the keener appreciation for monochrome.
In monochrome representation the eye has to deal only with one mode of perception—that of form. The perception of colour depends upon the differentiation of the effect upon the optical nerve fibres, that of form on the numbers and relative position of the latter. ”

“ In the author’s colour nomenclature, a monochrome is qualitatively described by a single term, and a complex colour by a combination of two single terms. For a quantitative description, it is only necessary to add the measured [76] unit value to each term. When there is excess of brightness, or a saddening factor, these also must be quantitatively estimated.
The colours developed by means of these scales are governed by the same law of selective absorption which governs the development of natural colours, any of which can be matched and reproduced by means of their established ray proportions. ”

“ When it is desired to convert a monochrome image into a multi-coloured map, as many stones as there are colours to be used must be first ground and polished with oxalic acid till they have a high polish. ”

“ We now come to painting. Begin on porcelain by a plate, and on earthenware by a tile. If the pupil has had no practice either in water colors or in oils—if, in a word, has no idea as yet of setting a palette, undertake first a monochrome, that is to say, a painting done with one color only, heightened by one or two other tones.
112Monochromes are made in the following tints: Grisailles, green, blue-green, blue, violet of iron, carmine, purple capucine red, sepia, red brown, bitumen. ”

“ It must have been, for a true artist, delightful to triumph over the difficulty of achieving the effects of relief and of modelling with the aid of a single pigment only. To be the master of such an art, and to handle the monochrome in such a way as to run with perfect touch through a gamut of gradations in tone, would surely have been more gratifying than to win success by the splendour of full illumination. The artist did not, however, entirely abstain from the use of gold; he allowed it to shine on the crowns of kings and around the heads of his saints ”

“ At the end of April some monochromes had been sent for reproduction, but he was greatly disappointed with them, as may be seen by the diary:—
"May 31. Had a great deal of trouble this month about reproductions of drawings in autotype. Dissatisfied with the reproductions of the oil monochromes, which came coarse, with thousands of false specks of light. The surface of a drawing should be mate for autotype reproduction. This led me to make various experiments of various kinds, and the latest conclusion I have arrived at is something like drawing on wood ”

“ 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. ”

“ Visual estimates of color, without the help of any standard for comparison, are continually distorted by doubt, guess-work, and the fatigue of the eye. Hardly two persons can agree in the intelligible description of color. Not only do individuals differ, but the same eye will vary in its estimates from day to day. A frequent assumption that all strong pigments are equal in chroma, is 62 far from the truth, and involves beginners in many mishaps. Thus the strongest blue-green, chromium sesquioxide, is but half the chroma of its red complement, the sulphuret of mercury. ”

“ We choose carmine for the primary red as the color which gives the brightest purple with cobalt blue, at the same time that it gave the brightest orange with chrome yellow. Thus we have chrome (No. 1) , for yellow, cobalt for blue, and madder carmine for red. These are the primaries.
Colored objects appear colored owing to their action on light. This action consists in absorbing one or more of the different colored rays which fall upon it, and reflecting the rest; and it is these reflected rays that give the color to the object. Bodies which emit light are called luminous, as the sun. ”

“ For they become colour'd by reflecting the Light of their own Colours more copiously, and that of all other Colours more sparingly, and yet they do not reflect the Light of their own Colours so copiously as white Bodies do. If red Lead, for instance, and a white Paper, be placed in the red Light of the colour'd Spectrum made in a dark Chamber by the Refraction of a Prism, as is described in the third Experiment of the first Part of this Book; the Paper will appear more lucid than the red Lead, and therefore reflects the red-making Rays more copiously than red Lead doth. ”

“ 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. ”

“ When a corundum is tested on the refractometer in white light a wide spectrum deliminates the two portions of the field because of the smallness of the colour-dispersion (cf p. 25) . The dichroism of both ruby and sapphire is marked, the twin colours given by the former being red and purplish-red, and by the latter blue and yellowish-blue, the second colour in each instance corresponding to the extraordinary ray. Tests with the dichroscope easily separate ruby and sapphire from any other red or blue stone. This character has an important bearing on the proper mode of cutting the stones. ”

“ 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. ”

“ In one series of experiments the chromatic effect of 46·8 parts of black, 29·1 of yellow, and 24·1 of blue was found to be the same as that of 66·6 of101 red and 33·4 of green; each set of discs has a dirty yellow tinge.
Now, in this experiment, black is not a colour; practically no light reaches the eye from a dead black. We have, however, to fill up the circumference of the top in some way which will not affect the impression on the retina arising from the mixture of the blue and yellow; this we can do by using the black disc. ”

“ They are these: the image is formed of carbon or other known permanent pigment; the vehicle or menstruum in which the pigment is held is gelatine, rendered quite insoluble by combination with the oxide of chromium; the amount of gelatine present in the image, and uniting it with the paper on which it rests, is not greater than that on the surface of a sheet of well-sized writing-paper, so that there is as little danger of the vehicle cracking or decomposing, as there is of the pigment fading. Absolute imperishability cannot probably be predicated of any picture formed of pigments and paper ”

“ 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. ”

“ When the retardation of these oscillation frequencies is continued, as, for example, by the introduction of heavier atomic complexes for the simpler and lighter hydrogen atoms, the absorption curves due to oscillation will gradually be made to travel toward the red end of the spectrum and the color, naturally, will travel into the blue. A very well-known example of this is the increase in depth of the blue color possessed by certain dyes which accompanies an increase in the number of methyl groups introduced into the molecule. ”

“ 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. ”

“ When they impinge upon a metal refractory enough to bear their shock without fusion, they can raise it to a heat so white and luminous as to yield, when analyzed, all the colors of the spectrum. In this way the dark rays emitted by the incandescent carbons are converted into light rays of all colors. Still, so powerless are these invisible rays to excite vision that the eye has been placed at a focus competent to raise platinum-foil to bright redness without experiencing any visual impression. ”

“ We can do this by catching the coloured band in another prism, when the light now emerging will be found to be white. Every part of that spectrum consists of homogeneous light, i.e. light that cannot be further split up. The way in which the white light is so unravelled by the prism is this: As the light passes through the prism its different component coloured rays are variously deflected from their normal course, so that on emerging we have each of these coloured rays travelling in its own direction, vibrating in its own plane. ”

“ Now, although the light from the positive pole of the carbons is uniform in quality, it sometimes varies in quantity, as it is difficult to keep its image always in exactly the centre of the slit. If we can take one part of the light coming through the slit to form the spectrum, and another part to form the second patch of white light, then the brightness of the two will vary together. At first sight this might appear difficult to attain; but advantage is taken of the fact that from the first surface of the first prism P1 a certain amount of light is reflected. ”

“ A 60°-prism, for instance, cut from a cube of rock-salt, for the purpose of obtaining the refractive index of the mineral by the ordinary method of producing a spectrum and arranging it for minimum deviation of the refracted rays, affords but a single spectrum, or a single sharp image of the spectrometer slit when the latter is fed by pure monochromatic light instead of ordinary white light. This is true however the prism may have been cut, as regards its orientation with respect to the natural crystal faces. ”

“ We have an example of this always with us in the photograph, where red and blue, in relation to each other, certainly do not produce the same effects on the plate as they do on the eye; and as we have no accurate knowledge as to the effect of contiguous colours upon a normally monochromatic eye, we could hardly be certain of producing an accurate monochromatic imitation of a multi-coloured object, which would deceive that eye.
The case of a colour-blind human being is certainly not a normal case, so the shade value of the various colours to this eye could hardly be taken as a safe standard. ”

“ There are some other salts known to chemists which possess the property of dichroism, or double colour. The double cyanide of platinum and barium, for instance, appears violet when viewed in one direction, and yellow in another. Change of temperature is often sufficient to change the colour of bodies—white oxide of zinc, for example, becomes bright yellow when heated. Such instances might be supplied ad infinitum, but enough has been said to prove that colour, after all, is only an appearance, and not an essential property of bodies. ”

“ It must be remembered that the light in which the object is to be photographed must be the same as that in which the luminosity of the glasses or pigments is measured.
Action of the Spectrum on Chromic Salts.—The salts most usually employed in photography are the bichromates of the alkalis. The result of spectrum action is confined to its own most refrangible end, commencing in the ultra-violet and reaching as far as in the solar spectrum. Fig. 2 shows the relative action of the various parts of the spectrum on potassium bichromate. ”