Polychrome

“ The parrot made quite a long speech, flying high above the arch where Polychrome stood and then back to Cap'n Bill's shoulder. Said he,
"We Pollys know our business, and we're all right! We'll take good care of Cap'n Bill and Trot and Button-Bright. You watch 'em from the Rainbow, and I'll watch day and night, And we'll call a sky policeman if trouble comes in sight!"
Suddenly, the bow lifted and carried the dancing maidens into the sky. The colors faded, the arch slowly dissolved and the heavens were clear. Trot turned to the Pinkies. "Let's have a holiday today," she said. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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 dark green pigment prepared from oxide of chromium; mixed with Prussian blue and chrome yellow it is called Green Cinnabar.
Chrome Ochre. Oxide of chromium of a fine yellowish green.
Chrome Red. A chromate of lead; a durable pigment used in oil painting. (See Red Lead.)
Chrome Yellow. A chromate of lead, which makes a bad pigment for oil painting. It is very poisonous and not durable; when mixed with white lead it turns to a dirty grey. As a water-colour pigment it is less objectionable. ”

“ 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. ”

“ The pigments are white, yellow ochre, chrome yellow light, chrome yellow medium, and chrome yellow dark, burnt and raw sienna, turkey and raw umber, ultramarine and ivory black. The greens are preferably mixed by adding ultramarine to one of the chromes. Shades are formed by the addition of the siennas, umbers, or black. Black and white, mixed to a gray, are useful in reducing the chroma of a hue. The stains should be mixed with hot water and a small amount of glue for a binder. White occasionally comes prepared with glue in its composition. ”

“ 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. ”

“ The use of polarized light upon paint is valuable on account of its action upon crystalline substances. The re-enforcing pigments, such as Asbestine, China Clay, Gypsum, Silex, Barytes, etc., are crystalline and consequently act upon the polarized light. ”

“ It will be remembered that the chroma of the sphere ceased with 5 at the equator. The color tree prolongs 24 this through 6, 7, 8, and 9. The branch ends carry colored balls, representing the most powerful red, yellow, green, blue, and purple pigments which we now possess, and could be lengthened, should stronger chromas be discovered.12
(35) Such models set up a permanent image of color relations. Every point is self-described by its place in the united scales of hue, value, and chroma. These scales fix each new perception of color in the child’s mind by its situation in the color solid. ”

“ 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 ”

“ Chrome yellows are chromates of lead, produced by mixing dilute solutions of acetate or nitrate of lead and bichromate of potash. This makes a medium tint known as middle chrome. The addition of sulphate of lead makes this paler, when it is known as lemon chrome, whereas the addition of caustic lime makes an orange chrome of a darker color. The chromes mix well with oil and with white lead either in oil or water. They stand the sun well, but like other lead salts, become dark in bad air. ”

“ 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. ”

“ The glands contain coloring matter, and the changes of color in the frog's skin are due to the distribution of these pigment-cells, and the power they have of shrinking or contracting under nerve irritation. The pigment varies in individuals and in different parts of the body. Brown, black, yellow, green, and red are the colors most frequently observed. The color-cells are technically known as chromatophores. If the web of a frog's foot be placed on the stage of a microscope and examined with an achromatic lens, the chromatophores can readily be made out. ”

“ The negative taken is absolutely dense except where the lines of the drawing have affected it, and these are absolutely clear, admitting the unrestricted passage of light through them. A piece of planished copper or zinc is prepared or made sensitive to light by a preparation of albumen or gelatin and bichromate of potash spread upon its surface. The negative is laid upon the sensitized metal and placed in the light in the way an ordinary photograph is printed. The light passes through the transparent lines of the negative and hardens the bichromated film beneath them. ”

“ 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 ”

“ There are many who almost confine their attention to polarized light and its beautiful effects. Such would not deem these efforts to aid the student in cutting sections complete without some notice of those which are taken from various crystals, in order to display that curious and beautiful phenomenon, the rings with a cross. The arrangement of these is somewhat changed by the crystal which affords the section; but nitrate of potash gives two sets of rings with a cross, the long line of which passes through both, the short line dividing it in the middle. ”

“ 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. ”

“ 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. ”

“ Upon the mode of manufacture depend not only the beauty of the colour but its stability. If properly and carefully prepared, it is of a vivid lemon tint, deep or pale, very clear, very pure and permanent. It also washes well, and is entirely free from the slightest tinge of orange. This may be pronounced the only chromate which possesses durability, not being liable to change by damp or foul air, by the action of light or the steel palette-knife, or by mixture with white lead and other pigments, either in water or oil, in both of which it works pleasantly. ”

“ Chromotrope, Chrome Brown, Chromogen, Alizarin Yellow, &c., the dyeing in an acid bath is followed by a treatment with a boiling solution of bichromate of potash, alum, or chromium fluoride, whereby the colouring matter on the fibre is changed into insoluble oxidation products or colour-lakes. This operation of developing or fixing the colour is effected either in the same bath at the end of the dyeing operation, or in a separate bath. See also Artificial Mordant Colours. ”

“ The erio chrome colours (black, brown, red, &c.) are applied in wool dyeing like diamond black.
Chromotrope, of which there are several brands, is an Acid Colour which is applied to wool in an acid bath in the usual manner. The red or purple colours thus obtained are saddened in the same bath with bichromate of potash and changed into black, the colouring matter being oxidized and simultaneously combined with chromium. ”

“ The mode of application of the two classes of colours is, of course, in each case quite essentially different, for in the case of the monogenetic class the idea is mainly either to dye at once and directly upon, the unprepared fibre, or having subjected the fabric to a previous preparation with a metallic or other solution, to fix directly the one colour on that fabric, on which, without such preparation, it would be loose. In the case of the polygenetic class, the idea is necessarily twofold. The dyeing materials are not colours, only colour generators. ”

“ 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. ”