Is a pale ultramarine, with a cobalt hue; and, in spite of its name, less permanence than belongs to the richer and deeper sorts. What Antwerp blue is to Prussian blue, this is to French blue—that is, as regards colour. With respect to durability, however, permanent and Antwerp blues cannot be compared; the former being a weakened variety of a stable, and the latter a weakened variety of a semi-fugitive, pigment. Hence permanent blue justifies its name, although that name would be more suited to the brilliant, or French, ultramarine.
136. GENUINE ULTRAMARINE,
Native Ultramarine, Natural Ultramarine, Real Ultramarine, True Ultramarine, Ultramarine, Pure Ultramarine, Azure, Outremer, Lazuline, Lazulite Blue, and Lazurstein. This most costly, most permanent, and most celebrated of all pigments, is obtained by isolating the blue colouring matter of the lapis lazuli, a stone chiefly brought from China, Thibet, and the shores of Lake Baikal. About the antiquity of the stone, and its colour, much has been written, and many conflicting statements have been made; but there is little doubt that our lapis lazuli was the sapphire of the ancients; and that the first certain mention of ultramarine occurs in a passage of Arethas, who lived in the eleventh century, and who, in his exposition of a verse in the book of Revelation, says, the sapphire is that stone of which lazurium, as we are told, is made. It has been common to confound ultramarine with the cyanus and cœruleum of the ancients; but their cyanus, or Armenian blue, was a kind of mineral or mountain blue, tinged with copper; and their cœruleum, although it may sometimes have been real ultramarine, was properly and in general a copper ochre. That ultramarine was known to the ancients there seems every probability, for it is certain they were acquainted with the stone; and modern travellers describe the brilliant blue painting still remaining in the ruins of temples of Upper Egypt as having all the appearance of ultramarine. Whether it is so or not, however, could only be proved by analysis; for, be it recollected, although the colour had preserved its hue during so many centuries, it had been completely buried, and therefore most perfectly secluded from light and air. Mr. Layard, in his 'Nineveh,' referring to some painted plaster, remarks that "The colours, particularly the blues and reds, were as brilliant and vivid when the earth was removed from them as they could originally have been; but, on exposure to the air, they faded rapidly." In all likelihood, these were of organic, or semi-organic, origin, prepared in some such manner as that mentioned by Pliny, who speaks of an earth which, when boiled with plants, acquired their blue colour, and was in some measure inflammable. As a pigment, cobalt was unknown to the ancients; but to these vegetable and copper blues of theirs, a third blue may perhaps be added. Experiments made upon blue tiles, found in a Roman tesselated foot-pavement at Montbeillard, showed that the colour was due to iron. M. Gmelin has proved that a blue tint can be imparted to glass and enamel by means of iron; and it is probable that the ancients were first induced by the blue slag of their smelting-houses to study the colouring of glass with iron; that in this art they acquired a dexterity not possessed at present, and that they employed their iron-smalt as a pigment, as we do our smalt of cobalt. To sum up, there are grounds for believing that the ancients were acquainted with copper blues, vegetable blues, and iron blues; and that, consequently, the blue described by travellers as having all the appearance of ultramarine may, or may not, be that pigment.
Lapis lazuli, or lazulite, is usually disseminated in a rock, which contains, among other substances, a fine white lazulite. In the Musée Minéralogique of Paris are two splendid specimens of the stone, in which is seen the transition from the azure to the white. According to the quantity and quality of blue present, the lapis varies from an almost uniform tint of the deepest indigo-blue to grayish-white, dotted and streaked at intervals with pale blue. The exceeding beauty of good samples has caused the lazulite to be much sought after, both as a gem for adorning the person, and for inlaid works in ornamental decoration. In China the stone is highly esteemed, being worn by mandarins as badges of nobility conferred only by the Emperor; and in the apartments of a summer palace near St. Petersburg, the walls are covered with amber, interspersed with plates of this costly lapis. Besides the colouring principle of the lazulite, there are always more or less mica and iron pyrites, the latter a lustrous yellow bisulphide of iron, which has often been mistaken for pellets of gold. Having chosen portions of the stone most free from these impurities, it is simply requisite to reduce them to an impalpable powder to obtain a blue pigment; and probably this was the original mode of preparing it before the discovery of the modern process. This curious method, which is mechanical rather than chemical, depends for its success on the character and proportions of the materials employed, as well as on the nicety of working. When well carried out, it perfectly isolates the blue from all extraneous matter, yielding the colour at first deep and rich, then lighter and paler, and lastly of that gray tint which is known by the name of Ultramarine Ash. The refuse, containing little or no blue, furnishes the useful pigment, Mineral Gray.
The immense price of ultramarine—or, as it was at first called, azurrum ultramarinum, blue beyond-the-sea—was almost a prohibition to its use in former times. It is related that Charles I. presented to Mrs. Walpole, and possibly to Vandyke also, five hundred pounds worth of ultramarine, which lay in so small a compass as only to cover his hand. Even in these days, despite the introduction of artificial ultramarines, the native product continues costly, commanding in proportion to its intensity and brightness, from two to eight guineas an ounce. To say, however, that the merits of the blue at least equal its expense, is to give the genuine ultramarine no more than its due. It has, indeed, not earned its reputation upon slight pretensions, being, when of fine quality, and skilfully prepared, of the most exquisitely beautiful blue, ranging from the utmost depth of shadow to the highest brilliancy of light and colour,—transparent in all its shades, and pure in all its tints. A true medial blue, when perfect, partaking neither of purple on the one hand, nor of green on the other, it sustains no injury either by damp and impure air, or by the intensest action of light, and is so eminently durable, that it remains unchanged in the oldest paintings. Drying well, working well in oil and fresco, ultramarine may be safely compounded with pigments generally, excepting only an acid sulphate of baryta or constant white. The blue has so much of the property of light in it, and of the tint of air—is so purely a sky-colour, and hence so singularly adapted to the direct and reflex light of the sky, and to become the antagonist of sunshine—that it is indispensable to the painter. Moreover, it is so pure, so true, so unchangeable in its tints and glazings, as to be no less essential in imitating the marvellous colouring of nature in flesh and flowers. To this may be added that it enters so admirably into purples, blacks, greens, grays, and broken hues, that it has justly obtained the character of clearing or carrying light and air into all colours, both in mixture and glazing, as well as gained a sort of claim to universality throughout a picture.
Nevertheless, ultramarine is not always entitled to the whole of this commendation. Frequently it is coarse in texture, in which case it is apparently more deep and valuable; yet such blue cannot be used with effect, nor ground fine without injuring its colour. Again, it is apt to be separated in an impure state from the lapis lazuli, which is an exceedingly varying and compound mineral, abounding with earthy and metallic parts in different states of oxidation and composition: hence ultramarine sometimes contains iron as a red oxide, when it has a purple cast; and sometimes the same metal as a yellow oxide, when it is of a green tone; while often it retains a portion of black sulphuret of iron, which imparts a dark and dusky hue. Occasionally, it is true, artists have preferred ultramarine for each of these tones; still are they imperfections which may account for various effects and defects of this pigment in painting. Growing deeper by age has been attributed to ultramarine; but it is only such specimens as would acquire depth in the fire that could be subject to the change; and it has been reasonably supposed that in pictures wherein other colours have faded, it may have taken this appearance by contrast. Ultramarine, prepared from calcined lapis, is not liable to so deepen; but this advantage may be purchased at some sacrifice of the vivid, warm, and pure azure colour of the blue produced from unburnt stone. We have frequently found ultramarine to be darkened, dimmed, and somewhat purpled by ignition; and the same results ensue, in many instances, when the lazulite is calcined. In burning the stone, the sulphur of the pyrites is in a great measure expelled, and during its expulsion has probably a deteriorating influence on the beauty of the colour: our belief in this being so is strengthened by the fact that certain samples of ultramarine, ignited with sulphur, were not improved thereby. Similar effects are likewise caused by a careless or improper mode of treatment, for the finest lapis may yield dingy blues, containing particles of mica, metal, &c., and possessing a dull green, black, or purple hue. Of course the perfection of the pigment is dependant to a large extent upon the quality of the stone itself.
Though unexceptionable as an oil-colour, both in solid painting and glazing, it does not work so well as some other blues in water; nor is it, unless carefully prepared, so well adapted for mixed tints, on account of a gritty quality, of which no grinding will entirely divest it, and which causes it to separate from other pigments. When extremely fine in texture, however, or when a considerable portion of gum, which renders it transparent, can be employed to give connexion or adhesion while flowing, it becomes no less valuable in water than in oil; but when its vivid azure is to be preserved, as in illuminated manuscripts and missals, little gum must be used. The fine greens, purples, and grays of the old masters, are often unquestionably compounds of ultramarine; and formerly it was the only blue known in fresco. Pure ultramarine varies in shade from light to dark, and in hue from pale warm azure to the deepest cold blue.
Native ultramarine consists of silica, alumina, sulphur, and soda; its colouring matter seeming to be due to hyposulphite of soda and sulphide of sodium. In these respects, as well as in that of being decolourised by acids, the natural product resembles the artificial. As a precious material, the former has been subject to adulteration; and it has been dyed, damped, and oiled to enrich its appearance; attempts of fraud, however, which may be easily detected. In the preceding edition of this work the author adds—"and the genuine may be as easily distinguished from the spurious by dropping a few particles of the pigment into lemon-juice, or any other acid, which almost instantly destroys the colour of the true ultramarine totally, and without effervescence." With this statement, so far as it pretends to be a test for the two kinds, we are not inclined to agree. Genuine ultramarine is always decolourised by acids; but it depends on the mode and nicety of its preparation whether it is decolourised without effervescence: that this is the case the author himself admits in his article on artificial ultramarine. Moreover, the "violent effervescence" which he describes as ensuing on the latter being dropped into an acid, does not of necessity take place: in M. Guimet's finest variety, the brilliant ultramarine, acid produces little or no effervescence. Seeing, therefore, that both sorts are decolourised by acids, and that both may or may not effervesce therewith, the acid test must be considered fallacious. Experiments made with different samples of each, showed that native ultramarines offered greater resistance to acid than the artificial, taking longer to decolourise; and that the residues of the first were in general of a purer white than those of the last. It was also found that the brilliant ultramarine, above referred to, was less readily decolourised than other French or German kinds.