Field's Chromatography Part 11

119. _Tin Pink._

By igniting strongly for some hours a mixture of stannic oxide, chalk, chromate of potash, and a little silica and alumina, a dingy red ma.s.s is obtained, which acquires a beautiful rose-red colour on being washed with water containing hydrochloric acid. For the same reason that the pinks of cobalt are superfluous as artistic pigments, this tin product is commercially ineligible. Having, however, the advantage of being cheap, and being probably durable, it would be well adapted for the common purposes of painting, in place of the fugitive rose pink.

120. _Ultramarine Red?_

In Gmelin's Handbook of Chemistry it is remarked that "Hydrogen gas pa.s.sed over ignited ultramarine, colours it light red, from formation of liver of sulphur, hydrosulphuric acid gas and water being evolved at the same time." On most carefully making the experiment with a sample of native blue (the variety referred to) we did not succeed in effecting this change: no alteration to red or even to purple took place, the only result being that the colour was entirely spoilt, having a.s.sumed a leaden slate-gray hue. At our request, the trial was kindly repeated by well-known chemists, who took every precaution to ensure success.

Several specimens of ultramarine were acted upon, but in no case was a red or anything like a red obtained, the products ranging from a slate-gray to a drab-grey. Sufficient hydrosulphuric acid gas was evolved to blacken paper moistened with acetate of lead, a fact which proved that the blue had lost some of its sulphur. Seeing that not only no red was produced, but that no tendency to red was imparted, is it possible the change described by Gmelin occurred under exceptional circ.u.mstances? All conversant with chemical matters will admit that results are obtained occasionally which cannot be repeated, owing it may be to some slight difference in the materials employed, or some slight variation of the process. Perhaps a link, considered of no importance at the time and overlooked, has been lost, and thus the whole chain of proceeding becomes useless. It is, therefore, within the bounds of probability that the red ultramarine of the great German chemist was furnished either by a peculiar specimen of blue, or by a modified form of the method he gives. We have noticed the subject at some length because if a red ultramarine, brilliant and durable, could be obtained, the colour might prove of value. A permanent artificial compound corresponding to French blue would certainly be an acquisition.

121. _Uranium Red._

By treating the yellow sulphite of uranium with a prolonged current of sulphuretted hydrogen, and saturating gradually with ammonia, a red finally results. This colour is insoluble in water, and it has the objection of remaining partially suspended for an almost indefinite time, colouring the liquid light red. The product is brighter and more beautiful while moist; when dried and powdered, its tone--slightly approaching vermilion--is duller. The colour may be obtained of several degrees of brilliancy, but, apart from the question of expense, it would be inadmissible in oil, the red gradually altering by contact therewith.

The most persistent tint at length resembles burnt Sienna.

122. _Wongshy Red._

There was imported a few years ago from Batavia a new colouring principle, under the name of _wongshy_, and consisting of the seed-capsule of a species of gentian. The aqueous extract, freed from the pectin which it contains, yields with baryta- and lime-water yellow precipitates, from which acids separate the colouring matter of a vermilion hue. When thus prepared it is insoluble in water, and would so far be adapted for a pigment. The red has not, however, been employed as such, and we are unacquainted with its habitudes.

The concluding remarks appended to the chapter on yellow apply equally to red, and indeed to all other colours. It is not a.s.sumed that the list is exhausted: there are other reds, but they are, like some we have mentioned, ineligible as pigments, either by reason of their fugacity, their costliness, the difficulty of producing them on a scale, or the sources whence they are derived being commercially unavailable. While endeavouring throughout the work to render complete the collection of pigments actually in use, it is our object to give a selection only of numbered italicised colours; ample enough, however, to include those which have become obsolete or nearly so, and full enough to afford some insight into our resources. The nearer we approach perfection, the more eager we are to arrive at it: the path before us, therefore, cannot fail to be of interest.

Looking back, and noting those pigments commonly employed, we find that the reds like the yellows are divisible into three cla.s.ses--the good, bad, and indifferent; or the permanent, the semi-stable, and the fugitive.

Among permanent reds, rank cadmium red, madder reds, Mars red, the ochres, and vermilions.

In the second or semi-stable cla.s.s, must be placed cochineal lakes, Indian lake, and red chrome.

To the third division, or the fugitive, belong dragon's blood, pure scarlet, red lead, and the coal-tar reds.

With regard to the foregoing cla.s.sification, it must be borne in mind that the properties and effects of pigments are much influenced by advent.i.tious circ.u.mstances. Sometimes pigments are varied or altogether changed by the grounds on which they are employed, the vehicles in which they are used, the siccatives and colours with which they are mixed, and the varnishes by which they are covered. And as there is no exact and constant agreement in different specimens of like pigments, so there is no exact and constant result in their use. Artists vary as much as the pigments they employ: some resemble the old masters in the delicacy with which they treat their colours, the cleanliness with which they surround them, and the care with which they compound them: in the hands of such artists pigments have every chance. Some, however, are characterized by a careless manipulation, a dirty mode of working, an utter disregard for all rules of admixture: with such painters the best colours may be ruined. And here, indeed, it may be asked, whether these latter are not more properly termed painters than artists, chiefly belonging as they do to that slap-dash school which manufactures pictures simply to sell them. Duly subordinated, the commercial side of art has a value which it were affectation to ignore; but to paint merely for the present, heedless of the future, is to sink art to the level of a trade, not the most honest. For it is the purchaser who suffers from the want of thought bestowed on the materials, the sloppy manipulation, the careless compounding; sins of omission and commission that cause him, on finding his picture becoming chaos, to join the detractors of modern pigments.

In cla.s.sifying colours therefore, those also should be cla.s.sified who use them:--into artists, whose love for art would render it more lasting than themselves; and into painters, whose motto is _Vita brevis est, Ars quoque_.

CHAPTER X.

ON THE PRIMARY, BLUE.

The third and last of the primary or simple colours is _blue_, which bears the same relation to shade as yellow to light. Hence it is the most retiring and diffusive of all colours, except purple and black; and all colours have the power of throwing it back in painting, to a greater or less extent, in proportion to the intimacy of their relations to light--first white, then yellow, orange, red, &c.

Blue alone possesses entirely the quality technically called 'coldness'

in colouring, and it communicates this property variously to all other colours with which it happens to be compounded. Most powerful in a strong light, it seems to become neutral and pale in a declining light, owing to its ruling affinity with black or shade, and its power of absorbing light. Consequently, the eye of the artist is liable to be deceived when painting with blue in too low a light, or toward the close of day, to the endangering of the warmth and harmony of his picture.

Entering into combination with yellow in the composition of all _greens_, and with red in all _purples_, blue characterizes the tertiary _olive_, and is also the prime colour or archeus of the neutral _black_, &c., as well as of the semi-neutral _gray_, &c.: it therefore is changed in hue less than any other colour by mixture with black, as it is likewise by distance. Blue is present subordinately in all tertiary and broken colours, and being nearest in the scale to black, breaks and contrasts powerfully and agreeably with white, as in pale blues, skies, &c. Being less active than the other primaries in reflecting light, it is sooner lost as a local colour by a.s.similation with distance. There is an ancient doctrine that the azure of the sky is a compound of light and darkness, and some have argued hence that blue is not a primary colour, but a mixture of black and white; but pure or _neutral_ black and white compound in infinite shades, all of which are neutral also, or _grey_.

It is true that a mixture of black and white is of a _cool_ hue, because black is not a primary colour, but a compound of the three primary colours in which blue predominates, a predominance which is rendered more sensible when black is diluted with white. As to the colour of the sky, in which light and shade are combined, that is likewise neutral, and never blue except by contrast; thus, the more the light of the sun partakes of a golden or orange hue, and the more parched and burnt the earth is, the bluer appears the sky, as in Italy and all hot countries.

In England, where the sun is cooler, and a perpetual verdure reigns, infusing blue latently into the landscape, the sky is warmer and nearer to neutrality, partaking of a diversity of greys, which beautifully melodize with blue as their key, and harmonize with the light and landscape. Therefore the colour of the sky is always a contrast to the direct and reflected light of the scene: if this light were of a rose colour, the neutral of the sky would be converted into green, or if purple, the sky would become yellow. Similarly would it be in all cases, according to the laws of chromatic equivalence and contrast, as may be often seen in the openings of coloured clouds at the rising and setting of the sun.

In art, blue is apt to be discordant in juxtaposition with green, and less so with purple, both which are cool colours; consequently blue requires its contrast, _orange_, in equal proportion whether of surface or intensity, to compensate or resolve its dissonances and correct its coldness. In nature, however, blue is not discordant with either green or purple, nor are any two colours (as we have said before) ever found so. On the palette of nature each _colour_ is an example of _colouring_: no colour is too absolute or defined, no perfectly pure blue appears beside a perfectly pure green. A blue flower nestled in its green leaves does not offend the nicest eye, but the blue and green are not blue and green alone. There is, perhaps, but a single gleam of pure colour in each: the rest is composed of such varied hues and tints and shades, so broken and blended and beautifully harmonized, that no jarring discord is possible. Hue melts into hue, tint into tint, shade into shade; and thus does the simplest weed teach a lesson in colouring the proudest painter may stoop to learn.

We have spoken of blue, which is termed a cold colour, as retiring; and of yellow and red, which are called warm colours, as advancing. By this we must not be understood to mean that blue, as blue, expresses distance; or that yellow and red, as yellow and red, express nearness.

Colours are advancing or retiring in their _quality_--as depth, delicacy, &c., not in their hue. A blue object set side-by-side a yellow one will not look an inch farther off, but a red or orange cloud, in the upper sky, will always seem to be beyond a blue cloud close to us, as it is in reality. We grant that in certain objects, blue is a _sign_ of distance, but that is not because blue, as a mere colour, is retiring; but because the mist in the air is blue, and therefore any warm colour which has not strength of light enough to pierce the mist is lost or subdued in its blue. Blue in itself, however, is no more, on this account, retiring, than brown is retiring, because when stones are seen through brown water, the deeper they lie, the browner they appear.

Neither blue nor yellow nor red possesses, as such, the smallest power of expressing either nearness or distance; they merely express themselves under the peculiar circ.u.mstances which render them at the moment, or in that place, signs of nearness or distance. Thus, purple in a violet is a sign of nearness, because the closer it is looked at the more purple is seen; but purple in a mountain is a sign of distance, because a mountain close at hand is not purple, but green or grey. It may, indeed, be generally a.s.sumed that a tender or pale colour will more or less denote distance, and a powerful or dark colour nearness; but even this is not always so. Heathery hills will usually give a pale and tender purple near, and an intense or dark purple far away: the rose colour of sunset on snow is pale on the snow at one's feet, but deep and full on the snow in the distance; and the green of a Swiss lake is pale in the clear waves on the beach, but intense as an emerald in the sunstreak, six miles from sh.o.r.e. And in any case, when the foreground is in strong light, with much water about it or white surface, casting intense reflections, all its colours may be perfectly delicate, pale, and faint; while the distance, when it is in shadow, may relieve the whole foreground with deepest shades of purple, blue green, or ultramarine blue.

There is one law, however, about distance, which has some claims to be considered constant, namely, that dulness and heaviness of colour are more or less indicative of nearness. All distant colour is pure colour: it may not be bright, but it is clear and lovely, not opaque nor soiled; for the air and light coming between us and any earthy or imperfect colour, purify or harmonize it; hence a bad colourist is peculiarly incapable of expressing distance. It is not of course meant that bad colours are to be used in the foreground by way of making it come forward; but only that a failure in colour there will not put it out of its place. A failure in colour in the distance will at once do away with its remoteness; a dull-coloured foreground will still be a foreground, though coloured badly; but an ill-painted distance will not be merely a dull distance, it will be no distance at all.

This seeming digression is not out of place, as it will enable the artist better to understand that it is in their quality, not in their hue, that colours are advancing or retiring; and that he must rely on the depth, delicacy, &c., of his pigments, and not simply on their colours, to produce effects of distance.

Of all colours, except black, blue contrasts white most powerfully. In all harmonious combinations of colours, whether of mixture or neighbourhood, blue is the natural, prime, or predominating power.

Accordingly, blue is universally agreeable to the eye in due relation to the composition, and may more frequently be repeated therein, pure or unbroken, than either of the other primaries; whence the employment of ultramarine by some masters throughout the colouring of a picture.

Blue pigments, like blue flowers, are more rare than those of the other primary colours. In permanent blues the palette is very deficient, the list being exhausted when the native and artificial ultramarines and the cobalts have been mentioned. That there is room for new blues, durable and distinct, cannot therefore be denied. A good addition has been made of late years in the German _Coelin_, known here as Cerulian Blue and Coeruleum. What is chiefly wanted, however, is a colour combining the wonderful depth, richness, and transparency of Prussian blue with the strict stability of ultramarine. A permanent Prussian blue would be the most valued gift the palette could receive.

COBALT BLUES

comprise _Cerulian Blue_ or _Coeruleum_, _Cobalt Blue_, _Smalt_, _Royal Blue_, _Dumont's Blue_, _Saxon Blue_, _Thenard's Blue_, _Leithner's Blue_, _Hungary Blue_, _Dutch Ultramarine_, _Zaffre or Enamel Blue_, _Vienna Blue_, _Paris Blue_, _Azure_, &c., and are obtained by the action of heat on mixtures of earthy or metallic bases with cobalt. They are divisible into three cla.s.ses--the stannic cerulian blue, the aluminous cobalt blues, and the siliceous smalts. Of these, the first possesses the least depth; the second hold a middle position; while the third are marked by exceeding richness. Although not to be ranked with ultramarine, the stannic and aluminous blues may be described as durable, or at least as durable rather than semi-stable.

There are, as we have before observed, different degrees of permanence, and the blues in question are not readily affected. With regard to smalts, they are, as artist's pigments, inferior in stability to other blues of cobalt.

123. CERULIAN BLUE,

or _Coeruleum_. Under the name Coelin there has of late years been imported from Germany the cobalt blue with a tin base to which reference has just been made. This comparatively new pigment--which likewise contains or is mixed with gypsum, silica, and sometimes magnesia--has the distinctive property of appearing a pure blue by artificial light, tending neither to green on the one hand nor to purple on the other.

This advantage, added to its permanence, has conferred a popularity upon coeruleum which its mere colour would scarcely have gained for it. 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 coeruleum becomes of service, as our present system of lighting picture galleries by gas affects the purity of blues generally. If those galleries were illuminated by means of the electric light, we have it on the authority of Chevreul that all colours and shades would show as well as by day: the same purpose would be answered by the magnesium light. Some artificial lights are the ruin of colours; in the soda flame (alcohol and salt) for instance, yellow chromate of lead appears white, while red ochre and aniline blue appear black.

Like other blues of cobalt, coeruleum a.s.sumes a greenish obscurity in time, but like them it resists for a lengthened period both the action of light and impure air, although chemically it is more open to the influence of the latter, owing to its tin base. In admixture it may safely be employed, as well as in fresco or enamel. For stage skies, &c., in high-art scenery, the blue is admirably adapted. Now that there are so many scene-painters who are artists--and so many artists who are scene-painters--in bringing Nature to the foot-lights the effect of gas on colours is of importance.

124. COBALT BLUE,

to which the various appellations have been given of _Thenard's Blue_, _Vienna Blue_, _Paris Blue_, _Azure_, _Cobalt-Ultramarine_, &c., is the name now exclusively confined to that preparation of cobalt which has a base of alumina. It may, therefore, be not improperly called a blue lake, the colour of which is brought up by fire, in the manner of enamel blues. The discovery of this important pigment was made in 1802 by M.

Thenard, who obtained it by calcining a well-combined mixture of alumina and crystals of cobalt. There may be employed with the aluminous base, either the a.r.s.eniate, the borate, or the phosphate of cobalt; but the latter in preference, as it produces the purest colour. The a.r.s.eniate has always a violet tinge, more visible by gas-light than by day; while, on account of the a.r.s.enic, the blue is more apt to be greened by impure air, by reason of the formation of yellow sulphide of a.r.s.enic. 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, from nickel also. With the absence of these and proper skill, a true and brilliant blue may be produced, almost rivalling the finest ultramarine. Apart, too, from its increased beauty, a cobalt blue containing no iron or nickel is of greater permanence than the ordinary products, being less liable to that greenness and obscurity which time confers.

Though not possessing the body, transparency, and depth of ultramarine, nor its natural and modest hue, commercial cobalt blue works better in water than that pigment in general does; and is hence an acquisition to those who have not the management of the latter. Resisting the action of strong light and acids, its beauty declines by time, while impure air greens and ultimately blackens it. Nevertheless, these changes are not readily effected, especially in well made samples full of colour, and sometimes the green tone is mechanically imparted. What wheat is to a loaf, colour is to a pigment--it has to be ground and made up for use; in the one vehicle to be mixed with gums, in the other with oils. It often happens that colours have an antipathy to the latter, and refuse to compound kindly therewith. Occasionally this repugnance manifests itself in a few days, occasionally not for months. We know of a green which flatly declines to have anything to do with oils, sinking and separating therefrom in the course of a week, and leaving the clear oil on the top. Repeatedly have colours to be coaxed to behave themselves as pigments, coaxed not to 'run,' to work well, to dry well, &c.; and in the humouring of their likes and dislikes the skill and patience of the artist-colourman are sometimes severely taxed. Given a colour, it might puzzle most chemists to convert it into a pigment; luckily Commerce lends her aid. Lasting success, it is true, does not always follow, and oils will rise to the surface now and then, giving green hues to blues, orange hues to reds, and buff hues to yellows. Hence changes of colour have been imputed before now to chemical alteration, when in reality the results have been physical, caused by the subsidence of the pigments, and the floating of the vehicles employed.

Cobalt blue dries well in oil, does not injure or suffer injury from pigments in general, and may be used with a proper flux in enamel, as well as in fresco. It affords clear bright tints in skies and distances, but is apt to cause opacity if brought too near the foreground, and to a.s.sume a violet tinge by artificial light. With madder brown it yields a range of fine pearly neutrals; and with light red, in any proportion, gives beautiful cloud tints. In combination with aureolin and sepia, or rose madder, cobalt furnishes most agreeable and delicate tints for distant trees, when under the influence of a soft light, or hazy state of the atmosphere. In water-colour painting, cobalt is tolerably firm on paper, and consequently answers better for some purposes than French blue. In middle distances, if the cobalt possess a tendency to chalkiness, the addition of a little indigo is a good corrective, especially where the blue tone is required to be sombre and dark: it should, however, be observed that the change is but temporary, indigo being a fugitive pigment. In marine painting in water-colours, cobalt is most useful for the remotest parts of seas and headlands. When dry, it can be changed by going over it with a slight wash of vermilion or light red, whereby a prismatic character is realized. Any strength of tone can be obtained by repeating the washes, and should the colour be too powerful, it may be reduced by pouncing it with a soft wet sponge; or if too cold and blue, by a thin wash of burnt Sienna, merely the water stained.

The blues of cobalt, on whatever base they may be prepared, are distinguished from native and artificial ultramarines by not being decolorised by acids.

125. SMALT,

Invented about the year 1540, in Saxony, is a vitreous compound of cobalt and silica, in fact a blue gla.s.s. Since the fifteenth century, cobalt has been used in different parts of Europe to tinge gla.s.s; and so intense is the colouring power of its oxide, that pure white gla.s.s is rendered sensibly blue by the addition of one thousandth part, while one twenty-thousandth part communicates a perceptible azure tint. In common with cobalt blue, the name _Azure_ has sometimes been given to it.

Varying exceedingly in quality and colour, the rougher kinds have been employed by the laundress, and in the making of porcelain, pottery, stained gla.s.s, encaustic tiles, &c.; as well as to cover the yellow tinge of paper. For this last purpose, however, smalt is not perfectly adapted, the colour being difficult to lay on uniformly, and the paper when written on blunting the nibs of pens. Hence it has been superseded to a great extent by artificial ultramarine, the presence of which may be detected by the yellow spot which a drop of acid leaves on the paper.

A coa.r.s.e gritty texture is peculiar to smalt, whether it be the _Powder Blue_ of the washtub and _Blue Sand_ of the pottery, or the _Dumont's_ and _Royal Blue_ of the artist and high-cla.s.s manufacturer. But the strict stability which is a feature in smalt when used for painting on gla.s.s and enamel does not follow it to the studio: both in water and oil its beauty soon decays, as is often the case with other vitrified pigments; nor is it in other respects eligible, being, notwithstanding its richness and depth, very inferior to the cobalts preceding. It may seem a paradox that the same colour should be at once so durable and so fugitive, but we may briefly explain it by saying _when vitreous pigments are reduced to that extreme state of division which the palette requires, they lose the properties they possess in a less finely divided state_. The best smalt in lumps appears black, yields a blue powder on grinding, becomes paler on further grinding, and may be almost decolourised by continued and excessive grinding. Smalt, it has been stated, is merely a blue gla.s.s; and when a piece of blue gla.s.s, or a blue crystal of sulphate of copper, is reduced to the fineness of flour, the blue is lost. In vitrified and crystallised compounds, colour depends on cohesion: sufficiently separate the particles, and the colour more or less disappears. Not only, moreover, does grinding effect an optical change in vitreous pigments, but it imposes further alteration.

That colour which was safe when locked up in a ma.s.s, crushed to minute atoms is no longer so: imbedded in gla.s.s or enamel it will endure for ages, but ground to impalpable powder becomes as liable to influence as though it had never been subjected to heat at all. To sum up, vitreous pigments are durable in a coa.r.s.e or compact form, but are not more stable than others when reduced to extreme division. As far as regards artists' colours, therefore, vitrification does _not_ impart permanence.

The grittiness to which we have referred is one of the defects of smalt, which cannot, consistently with preserving its colour be entirely freed from that drawback--an objection which pertains to vitreous pigments in general. Hence it does not wash well, and in mural decoration is sometimes applied to work by strewing the dry powdered colour upon a flat ground of white or blue oil paint immediately after the latter is laid on, whilst it yet remains wet. Of little body, it is a vivid and gorgeous blue; bright, deep, and transparent, bordering on the violet hue. It is chiefly employed in illumination and flower painting. The inferior kinds of smalt are occasionally adulterated with chalk.

126. CYANINE.