Cobalt blue

“ For three parts of white glass (without lead) one part of washed diaphoretic antimony is to be taken; the substances are well ground together, and fused in the common way.
Blue Enamel.—This fine colour is almost always obtained from the oxide of cobalt or some of its combinations, and it produces it with such intensity that only a very little can be used, lest the shade should pass into black. The cobalt blue is so rich and lively that it predominates in some measure over every other colour, and masks many so that they can hardly be perceived; it is also most easily obtained. ”

“ A light and pleasing blue, with a greenish-grey cast by day, it possesses little depth or richness, and is far excelled in beauty by a good aluminous cobalt. A certain chalkiness, moreover, somewhat detracts from its transparency, and militates against its use in water. It is in oil, and as a night colour, that cœruleum becomes of service, as our present system of lighting picture galleries by gas affects the purity of blues generally. ”

“ It is completely unaltered by the atmosphere. The most powerful chemical reagents have but a slight action upon it, and their action is less the higher the temperature used in the manufacture. Cobalt blue is made by precipitating mixed solutions of a cobalt salt and alum, washing, drying, and igniting the precipitate. A product of pure blue colour is only obtained when alum absolutely free from iron is used. If but very small quantities of iron are present, the red ferric oxide has a very considerable influence on the shade of the product. ”

“ Cobalt Blue
Is used precisely as the emerald green. A thin and even wash is most essential in the first place, to be gradually tinted up with the same tint. A good deal of patience and manipulation is necessary to smooth 39 this most difficult colour into obedience. Young beginners will find it most irksome to handle, but it forms an agreeable variety amidst the other blues. It looks well for skies in tiny landscapes, and may be used for water, if copying the older missals, in which it will be seen that water is always blue. White ornamentations are used over it, to hide any defects. ”

“ A metal found in various combinations, from which various colouring matters are obtained of great use in the arts. Cobalt blue, a beautiful blue pigment, is obtained by mixing a salt of pure cobalt with a solution of pure alum, precipitating the liquid by an alkaline carbonate, washing the precipitate with care, drying and igniting it strongly. A fine green, known as Rinmann’s green, is similarly prepared. The chloride, the nitrate, and the sulphate of cobalt form sympathetic inks, which only become visible when the moisture is absorbed by the application of heat. ”

“ Transparent cobalt blue, a glaze color always, requires a ground of Prussian blue and white. Body cobalt is used as a solid color, and for a panel color on traps, breaks, and vehicles of that order it produces admirable and fetching effects. The glaze colors are best used in a flowing medium of elastic rubbing varnish, especially when body surfaces are being coated, and the brushes adapted to applying such colors are the 1 1/2-inch and the 2-inch badger flowing brush or a soft, half-elastic bristle brush suited to the size of the panels being coated. ”

“ The arseniate has always a violet tinge, more visible by gas-light than by day; while, on account of the arsenic, the blue is more apt to be greened by impure air, by reason of the formation of yellow sulphide of arsenic. The purity of the colour, however, does not altogether depend on the compound of cobalt used; in a great measure—as with other pigments—it rests on the purity of the materials. To obtain a perfect blue, neither inclining to purple nor green, the cobalt and alumina should be freed from iron, and the former, as much as possible, [193] from nickel also. ”

“ A mixture of any two bright primaries will produce a bright secondary, and any admixture of the third primary will make the secondary color produced much duller or blacker. We consider that would be the purest blue which gave the brightest green with yellow, at the same time that it gave the brightest purple with a red, and it was decided that cobalt blue was the pure primary, which was blue with regard to the yellow chosen. It is obvious that if the blue were a greenish blue, although it might give a very bright green with yellow, it would give but a dull purple with the red. ”

“ Of all the materials employed as pigments in the decoration of porcelain, the most important and the most widespread in use is cobalt-blue. It is said that this colour was first introduced into China from the west of Asia as early as the tenth century, but it does not appear to have been used for painting before the thirteenth century. In this connection mention may be made of a miniature vase at South Kensington of the cream-coloured Ting ware already alluded to, which is painted with indistinct markings in cobalt-blue. ”

“ From phosphate of cobalt a beautiful blue pigment is produced, called Thenard’s blue. It is said to have all the characters of ultramarine. Oxide of cobalt has the property of colouring glass blue; hence a glass formed of this oxide under the name of smalt is the blue colouring matter used for ornamenting porcelain and earthenware, for staining glass, for painting on enamel, &c. ”

“ As on the earliest productions of all the old china works, the decorations on the Plymouth examples are invariably blue; the blue at first being of a heavy, dull, blackish shade, but gradually improving, until, on some specimens which I have seen, it had attained a clear brilliance. Cookworthy, being a good chemist, paid considerable attention to the producing of a good blue, and was the first who succeeded in this country in manufacturing cobalt blue direct from the ore. Before this time the colour was prepared by grinding foreign imported zaffres with slab and muller ”

“ We have produced them by wet and dry methods, varying in brilliancy and beauty, but characterised generally by want of body, and frequently by a smalt-like grittiness. Chemically, good and stable colours, they are not received with favour on the palette, and certainly may be very well replaced by mixtures of cobalt blue and madder red. When a permanent compound is obtainable equal in colour to an original pigment, and superior in its physical attributes, no objection can fairly be taken to its artistic preference. ”

“ I cannot, however, deny that I have often lamented this loss when I saw the excellent blue in the painted windows at Gouda, Goslar, and other places; though its beauty is much heightened by the transparency of the glass, and the strong light that falls upon it from without.
I shall now proceed to the invention of the colour prepared from cobalt. About the end of the fifteenth century, cobalt appears to have been dug up in great quantity in the mines on the borders of Saxony and Bohemia, discovered not long before that period. ”

“ In the last case it usually is in needle-like crystals growing through calcite crystals, as at St. Louis, Mo., Keokuk, Iowa, and Antwerp, N. Y.
The Cobalt Group
As a metal, cobalt is hard, brittle, and of a grayish color, tinged with red. It was not recognized as a separate element until 1735, and even today is one of the minor metals. Cobalt, chromium and a little tungsten make the alloy stellite, which has come into large use in making high-speed tools. The oxide of cobalt (CoO) is “smalt,” used to give the blue color to porcelain, pottery, glass, tiles, etc. ”

“ Would not the arsenic, which is so often combined with cobalt, have given occasion to many reports respecting the dangerous properties of these minerals? And would not arsenic and bismuth have been sooner known, had preparations of cobalt been made at so early a period? It is a circumstance of great weight also, that in the places where the ancients had mines, and where antiquities painted or tinged blue, and resembling in colour that produced by cobalt, have been dug up, cobalt has not been discovered, or has been discovered only in modern times. ”

“ Cæruleum is a pale blue pigment consisting of a compound of the oxides of cobalt and tin. It is made by converting tin by the action of nitric acid into white stannic oxide, adding a solution of cobalt nitrate and evaporating to dryness in a porcelain dish whilst stirring; whilst still warm the powder is strongly ignited. In cæruleum the chemical combination is less firm than in the compounds of cobalt oxide with zinc oxide or alumina, strong hydrochloric and dilute sulphuric acids decompose it, continued treatment with nitric acid extracts all the cobalt. ”

“ New Blue is a pale variety of French Ultramarine.
Prussian Blue is ferrocyanide of iron. Antwerp Blue is a weaker variety of the same colour containing alumina. These colours are not altogether reliable, as they are subject to change.
Cobalt Violet is a purple colour made from cobalt, and is quite permanent.
Purple Madder is usually prepared from the madder root, and is permanent under ordinary conditions. Sometimes, however, it is prepared from Crimson Lake, in which case it is fugitive. ”

“ The best known sympathetic inks consist of solutions of cobalt salts, the writing done with which changes on heating from a nearly invisible pink to blue. This peculiarity of cobalt to form two series of salts containing different amounts of water was discovered in 1715 by Waiz.
Other compounds that may be used as sympathetic writing fluids include tannin, which forms ordinary ink on the addition of iron sulphate; cobalt nitrate which becomes blue on adding oxalic acid, and gold chloride which gives a purple colour with tin chloride. ”

“ More expensive than the madder colours, and without their purity, delicacy, depth, or transparency, cobalt reds have often been offered as pigments, and as often declined. A colour may be good in itself, but if there is something better and at the same time cheaper, its introduction into commerce is out of the question.
99. Copper Reds.
A somewhat finely coloured red oxide is produced by exposing to a white heat for twenty minutes, a mixture of certain proportions of blue vitriol, mono-carbonate of soda, and copper [165] filings. ”

“ Practically the entire Canadian output, most of which is smelted at plants in southern Ontario, is exported to England and the United States.
The cobalt can be plainly seen in the ore when the rock is exposed to the weather. It is of a steel-gray colour tinged with rose-pink, and where it occurs in the form of a powder it looks exactly like rouge. When heated it turns a beautiful blue. Arsenic and other elements are often found mixed with the cobalt-silver ore, and the region has deposits of nickel, copper, and lead. ”

“ Compound oxides. When the blue oxide of cobalt is precipitated from a solution, by an alkali or lime water, and oxymuriate of lime is gradually dropped in, the precipitate changes colour rapidly; it passes from blue to green and olive, thence to a dark bottle green, and finally becomes black; oxygen gas is given out copiously when an excess [Pg 70] of oxymuriate of lime is used. I find the additional oxygen requisite to convert the blue to the black oxide is what Proust states it, namely, 1⁄3 of that necessary to form the blue ”

“ A small quantity of the oxide of gold tints glass pink, but the colour becomes extremely rich and ruby-like, when a larger quantity of the oxide is employed. Oxide of cobalt in very small quantities yields, with silicic acid, an intensely blue silicate. This substance, carefully prepared in a special manner and ground to a fine powder, forms the well known water-colour pigment called smalt. Oxide of silver stains glass from a delicate lemon tint to a deep orange, in proportion to the quantity of the oxide employed. ”

“ When the powdered alumina compounds are strongly ignited in the oxidizing flame, then moistened with nitrate of cobalt, and re-ignited in the oxidizing flame, an infusible mass is left, which appears, when cooled, of an intense blue color. The presence of colored metallic oxides, in considerable quantity, will alter or suppress this reaction. The silicates of the alkalies produce, in a very strong heat, or continued heat, with nitrate of cobalt, a pale blue color. The blue color produced by alumina is only distinctly visible by daylight ”

“ A pigment obtained, usually by roasting cobalt glance with sand or quartz, as a dark earthy powder. It consists of crude cobalt oxide, or of an impure cobalt arseniate. It is used in porcelain painting, and in enameling pottery, to produce a blue color, and is often confounded with smalt, from which, however, it is distinct, as it contains no potash. The name is often loosely applied to mixtures of zaffer proper with silica, or oxides of iron, manganese, etc. ”

“ With age, however, it acquires a greenish tendency, and in artificial light it inclines to a violet tint. It is proof against acids and alkalies, and mixes particularly well with water. In combination with other pigments it is unaltered and has no effect on them. Its tones are different from those of ultramarine. It slowly decomposes when heated in strong sulphuric acid, yielding a violet solution and a white precipitate, which latter dissolves and affords a blue liquid on dilution with water. It consists principally of about 80 per cent. alumina, and 15 per cent. oxide of cobalt. ”

“ Until very recently the fine bluish tinge given to many writing papers was derived from the admixture of that expensive mineral blue, the oxide of cobalt, generally termed smalts, and which has still the advantage over the ultramarine of imparting a colour which will endure for a much longer period. One pound of ultramarine, however, going further than four of smalts at the same price, the former necessarily meets with more [97] extended application, and where the using is rightly understood, and the materials employed instead of being fine rags, comparative rubbish, excessively bleached ”