Field's Chromatography Part 16

The chief discord of green is blue; and when they approximate or accompany each other, they require to be resolved by the opposition of warm colours. It is in this way that the warmth of distance and the horizon reconciles the azure of the sky with the greenness of a landscape. Its less powerful discord is yellow, which needs to be similarly resolved by a purple-red, or its principles. In tone, green is cool or warm, sedate or gay, either as it inclines to blue or to yellow; yet in its general effects it is cool, calm, temperate, and refres.h.i.+ng.

Having little power in reflecting light, it is a retiring colour, and readily subdued by distance: for the same reason, it excites the retina less than most colours, and is cool and grateful to the eye. As a colour individually, green is eminently beautiful and agreeable, but it is more particularly so when contrasted by its compensating colour, red, as it often is in nature, even in the green leaves and young shoots of plants and trees. "The autumn only is called the painter's season," remarks Constable, "from the great richness of the colours of the dead and decaying foliage, and the peculiar tone and beauty of the skies; but the spring has, perhaps, more than an equal claim to his notice and admiration, and from causes not wholly dissimilar,--the great variety of tints and colours of the living foliage, accompanied by their flowers and blossoms. The beautiful and tender hues of the young leaves and buds are rendered more lovely by being contrasted, as they now are, with the sober russet browns of the stems from which they shoot, and which still show the drear remains of the season that is past."

The number of pigments of any colour is in general proportioned to its importance; hence the variety of greens is very great, though the cla.s.ses of those in common use are not very numerous. Of the three secondaries, green is the colour most often met with, and, consequently, the most often compounded: for this last reason, perhaps, the palette is somewhat deficient in really good original greens--more deficient than there is any necessity for.

CHROME OXIDES.

By numerous methods both wet and dry, oxides of chromium are obtainable pale and deep, bright and subdued, warm and cool, opaque and transparent: sometimes hydrated, in which case they cannot be employed in enamelling; and sometimes anhydrous, when they are admissible therein. But whatever their properties may be, chemical, physical, or artistic, they are all strictly stable. Neither giving nor receiving injury by admixture, equally unaffected by foul gas and exposure to light, air, or damp, these oxides are perfectly unexceptionable in every respect. For the most part they are eligible in water and oil, drying well in the latter vehicle, and requiring in the former much gum. They have long been known as affording pure, natural, and durable tints; but, until within the last few years, have been rather fine than brilliant greens. Lately, however, processes have been devised, yielding them almost as bright, rich, and transparent, as the carmine of cochineal itself.

175. OXIDE OF CHROMIUM,

_Opaque Oxide of Chromium_, _Green Oxide of Chromium_, _Chrome Oxide_, _True Chrome Green_, _Native Green_, _&c._, is found native in an impure state as Chrome Ochre, but is always artificially prepared for artistic use. Obtained anhydrous by dry modes, this is the only chrome oxide available in enamelling, and is the one seen on superior porcelain. It is a cold, sober sage green, deep-toned, opaque, and, although dull, agreeable to the eye. Its tints with white are peculiarly delicate and pleasing, possessing a silvery luminous quality, and giving the effect of atmosphere. Being very dense and powerful, it must be employed with care to avoid heaviness, and is preferably diluted with a large quant.i.ty of white, or compounded with transparent yellow. In the hands of a master, this gray-green furnishes l.u.s.trous hues with brown pink, Italian pink, and Indian yellow; three beautiful but fugitive pigments, of which the two last may be replaced by aureolin. Of this Mr. Penley observes, "as adapted for the colouring of foliage and herbage, it is impossible to say too much in its praise. It imparts the vividness and freshness of nature to every colour with which it is combined;" and he brackets oxide of chromium with aureolin as a compound hue "extremely useful." In flat tints, the oxide sometimes does not wash well in water.

176. TRANSPARENT OXIDE OF CHROMIUM

being deficient in body, is only eligible in oil. A very pale greyish-white green in powder, it gives an agreeable yellowish green of some depth in oil, moderately bright, but not very pure or clear.

We are acquainted with another transparent chrome oxide of far greater beauty, brightness, purity, and clearness than the above. Of a bluish green hue, a difficulty in getting it to mix with oil renders it at present unavailable.

177. VERONESE GREEN,

or _French Veronese Green_, is a comparatively recent introduction, similar in colour and general properties to the following; beside which, however, it appears dull, muddy, and impure. It is often adulterated with a.r.s.enic to an enormous extent, which interferes with its transparency, mars its beauty, and renders it of course rankly poisonous.

178. VIRIDIAN

is a still later addition to the palette, and the only permanent green which can be described as gorgeous, being not unlike the richest velvet.

Pure and clear as the emerald, it may be called the Prussian Blue of Greens, of such richness, depth, and transparency is it. In hue of a bluish-green, its deepest shades verge on black, while its light tints are marked by transparent clearness unsurpa.s.sed. No compound of blue and yellow will afford a green at once so beautiful and stable, so gifted with the quality of light, and therefore so suited for aerial and liquid effects. Used with aureolin, it gives foliage greens sparkling with suns.h.i.+ne; and, fitly compounded, will be found invaluable for the gla.s.sy liquidity of seas, in painting which it becomes inc.u.mbent to employ pigments more or less transparent. "The general failing in the representation of the sea is, that instead of appearing liquid and thin, it is made to bear the semblance of opacity and solidity. In order to convey the idea of transparency, some object is often placed floating on the wave, so as to give reflection; and it is strange that we find our greatest men having recourse to this stratagem. To say it is not true in all cases, is saying too much; but this we do a.s.sert, that as a general principle it is quite false, and we prove it in this way: water has its motion, more or less, from the power of the wind; it is acted upon in the ma.s.s, and thus divided into separate waves, and these individually have their surface ruffled, which renders them incapable of receiving reflection. The exception to this will be, where the heaving of the sea is the result of some gone-by storm, when the wind is hushed, and the surface becomes bright and gla.s.sy. In this state, reflections are distinctly seen. Another exception will be in the hollow portion of the waves, as they curl over, and dash upon the sh.o.r.e."

As viridian, like the sea, is naturally "liquid and thin, bright and gla.s.sy," the extract we have quoted from Mr. Penley, points to this green as a pigment peculiarly adapted for marine painting; in which, it may be added, its perfect permanence and transparency will be appreciated in glazing. Its fitness for foliage has been remarked; but in draperies the colour will prove equally useful, and in illumination will be found unrivalled. In the last branch of art, indeed, viridian stands alone, not only through its soft rich brilliancy, but by the glowing contrast it presents with other colours: employed as a ground, it throws up the reds, &c., opposed to it, in a marvellous manner. Like the three preceding oxides of chromium, viridian neither injures nor is injured by other pigments; is unaffected by light, damp, or impure air; and is admissible in fresco. In enamelling it cannot be used; the colour, depending on the water of hydration, being destroyed by a strong heat.

COPPER GREENS

are commercially known as _Emerald Green_, _Malachite Green_, _Scheele's Green_, _Schweinfurt Green_, _Verdigris_, _Green Bice_, _Green Verditer_, _Brunswick Green_, _Vienna Green_, _Hungary Green_, _Green Lake_, _Mineral Green_, _Patent Green_, _Mountain Green_, _Marine Green_, _Saxon Green_, _French Green_, _African Green_, _Persian Green_, _Swedish Green_, _Olympian Green_, _Imperial Green_, _Mitis Green_, _Pickle Green_, &c.

The general characteristics of these greens are brightness of colour, well suited to the purposes of house-painting, but seldom adapted to the modesty of nature in fine art; considerable permanence, except when exposed to the action of damp and impure air, which ultimately blacken most of them; and good body. They have a tendency to darken by time, dry well as a rule in oil, and are all more or less poisonous, even those not containing a.r.s.enic.

179. EMERALD GREEN,

_Schweinfurt Green_, _Vienna Green_, _Imperial Green_, _Brunswick Green_, _Mitis Green_, &c., is a cupric aceto-a.r.s.enite, prepared on the large scale by mixing a.r.s.enious acid with acetate of copper and water.

It differs from Scheele's Green, or cupric a.r.s.enite, in being lighter, more vivid, and more opaque. Powerfully reflective of light, it is perhaps the most durable pigment of its cla.s.s, not sensibly affected by damp nor by that amount of impure air to which pictures are usually subject: indeed it may be ranked as permanent both in itself and when in tint with white. It works better in water than in oil, in which latter vehicle it dries with difficulty. Bearing the same relation to greens generally as Pure Scarlet bears to reds, its vivid hue is almost beyond the scale of other bright pigments, and immediately attracts the eye to any part of a painting in which it may be employed. Too violent in colour to be of much service, it has the effect, when properly placed, of toning down at once, by force of contrast, all the other greens in a picture. If discreetly used, it is occasionally of value in the drapery of a foreground figure, where a bright green may be demanded; or in a touch on a gaily painted boat or barge. When required, no mixture will serve as a subst.i.tute. Compounded with aureolin, it becomes softened and semi-transparent, yielding spring tints of extreme brilliancy and beauty.

180. SCHEELE'S GREEN,

or _Swedish Green_, resembles the preceding variety in being a compound of copper and a.r.s.enic, and therefore rankly poisonous; but differs from it in containing no acetic acid, in possessing less opacity, and in having a darker shade. It is a cupric a.r.s.enite, with the common attributes of emerald green, under which name it is sometimes sold. Of similar stability, it must not be employed with the true Naples yellow or antimoniate of lead, by which it is soon destroyed.

Upon the lavish use of this dangerous pigment in colouring toys, dresses, paper-hangings, artificial leaves, and even cheap confectionery, it is not our province to enlarge: the constant-recurring diseases and deaths, which, directly or indirectly, result from the employment of a.r.s.enical pigments, are such every-day facts that they are merely deplored and forgotten. With a.r.s.enic on our heads, our clothes, our papers, our sweets, our children's playthings, we are so accustomed to live--and die--in a world of poison, that familiarity with it has bred contempt. Into the fatal popularity, therefore, of a.r.s.enical colours for decorative purposes, we shall not further enter; but it behoves us to deprecate their presence, and the presence of all poisonous pigments, in colour-boxes for the young. It is one of the pleasures of childhood to suck anything attractive that comes in its way, openly if allowed, furtively otherwise: and as in early life we have a preference for brilliancy, so vivid a pigment as Scheele's green is an object of special attention. Artistically, it matters little whether a pigment is noxious or not, but we hold that poison should not be put into the hands of the young; and indeed are of opinion that a box of colours is about the worst present a child can receive.

181. MALACHITE GREEN,

or _Mountain Green_, is met with in c.u.mberland, and is also found in the mountains of Kernhausen, whence it is sometimes called _Hungary Green_.

It is prepared from malachite, a beautiful copper ore employed by jewellers, and is a hydrated dicarbonate of copper, combined with a white earth, and often striated with veins of mountain blue, to which it bears the same relation that green verditer bears to blue verditer. The colour, which may be extracted from the stone by the process followed for native ultramarine, varies from emerald-green to gra.s.s-green, and inclines to grey. It has been held in great esteem by some, and considered strictly stable, on the a.s.sumption, probably, that a pigment obtained from a stone like ultramarine, and by the same method, could not be otherwise than permanent. That it is so, with respect to light and air, there is no denying; but the green, when separated from the ore and purified for artistic use, is merely a carbonate of copper, and therefore subject to the influence of damp and impure air, in common with other non-a.r.s.enical copper colours. As a pigment, native malachite green has the same composition, or very nearly the same, as that which can be artificially produced, and answers to the same tests. Water-rubs of the two varieties which we exposed to an atmosphere of sulphuretted hydrogen became equally blackened by the gas. Practically, there is little or no difference between them: both preserve their colour if kept from damp and foul air, both are injured by those agents, and both are liable to darken in time, especially when secluded from light. The artificial, however, can be obtained of a much finer colour than the natural, which it may be made to resemble by admixture with mineral gray. On the whole, they can scarcely be recommended for the palette, and are certainly inferior in durability to Scheele's and Schweinfurt greens. In fresco painting they have been p.r.o.nounced admissible; but, apart from the question of damp, we should deem the conjunction of lime with carbonate of copper not favourable to permanence. By the action of alkalies, even the native green malachite may be converted into blue; and it becomes a question whether the dingy greenish-blue on some ancient monuments was not originally malachite green.

182. VERDIGRIS,

or _Viride aeris_, is of two kinds, common or impure, and crystallized or _Distilled Verdigris_, or, more properly, refined verdigris. The best is made at Montpellier in France, and is a sub-acetate of copper of a bright green colour inclining to blue. The least durable of the copper greens, it soon fades as a water-colour by the action of light, &c., and becomes first white and ultimately black by damp and foul gas. In oil, verdigris is permanent with respect to light and air, but moisture and an impure atmosphere change its colour, and cause it to effloresce or rise to the surface through the oil. It dries rapidly, and is exceptionally useful with other greens or very dark colours. In varnish it stands better; but cannot be considered safe or eligible, either alone or compounded. Vinegar dissolves it, forming a solution used for tinting maps, and formerly much employed for colouring pickles, &c.

The painters, who lived at the time when the arts were restored in Italy, used this pigment; and the bright greens seen in some old pictures are made by glazings of verdigris. It is often largely adulterated with chalk and sulphate of copper.

183. MIXED GREEN

Green, being a compound of blue and yellow, may be got by combining those colours in the several ways of working--by mixing, glazing, hatching, or otherwise blending them in the proportions of the various hues required. To obtain a _pure_ green, which consists of blue and yellow only, a blue should be chosen tinged with yellow rather than with red, and a yellow tinged with blue. If either a blue or a yellow were taken, tinged with red, this latter colour would go to produce some grey in the compound, which would tarnish the green. The fine nature-like greens, which have lasted so well in some of the pictures of the Italian schools, appear to have been compounded of ultramarine, or ultramarine ashes and yellow. Whatever pigments are employed on a painting in the warm yellow hues of the foreground, and blue colouring of the distance and sky, are advantageous for forming the greens in landscape, &c., because they harmonize better both in colouring and chemically, and impart h.o.m.ogeneity to the whole: a principle conducive to a fine tone and durability of effect, and applicable to all mixed tints. In compounding colours, it is desirable not only that they should agree chemically, but that they should have, as far as possible, the same degree of durability. In these respects, aureolin and ultramarine, gamboge and Prussian blue, Indian yellow and indigo, are all judicious mixtures, although not all to be recommended.

PERMANENT YELLOWS. | PERMANENT BLUES.

| Aureolin. | Cerulian Blue.

Cadmium Yellow, pale. | Cobalt Blue.

Cadmium Yellow, deep. | Genuine Ultramarine.

Lemon Yellow. | Brilliant Ultramarine.

Mars Yellow. | French Ultramarine.

Naples Yellow, modern. | New Blue.

Ochres. | Permanent Blue.

Orient Yellow. | Raw Sienna. |

The foregoing yellows and blues are in no wise inimical to each other, and yield the best mixed greens, chemically considered, the palette can afford. In an artistic sense, we confess, the result is not so satisfactory: the list of blues, it must be admitted, being somewhat scant. Among the latter there is no pigment with the wonderful depth, richness, and transparency of Prussian blue, and none consequently which will furnish with yellow a green of similar quality. That the artist, therefore, will dispense with Prussian blue, it would be too much to expect. There is, however, less necessity for it since the introduction of viridian, a green resembling that which is produced by admixture of Prussian blue and yellow, and which may be varied in hue by being compounded with aureolin or ultramarine. Our object in this work is to give precedence to the chemical rather than the artistic properties of pigments, to separate the strictly stable from the semi-stable, and the semi-stable from the fugitive. A colour or a mixture may be chemically bad but artistically good, and vice versa; but the chemist looks upon no pigment or compound with favour unless it be perfectly permanent, and ignores its mere beauty when void of durability. Hence, all artistic considerations are set aside in our lists of permanent pigments: if it be possible to use them alone, so much the better for the permanence of painting; if not, so much the worse will it be, according to the degree of fugacity of the colours employed.

184. BRONZE,

and the three succeeding varieties, are greens resembling each other in being semi-stable, and more or less transparent. Bronze is a species of Prussian green, of a dull blue-black hue. In its deep washes it appears a greenish-black with a coppery cast. It is used in ornamental work, and sometimes as a background tint for flower pieces.

185. CHROME GREENS,

commonly so called, are compounds of chromate of lead and Prussian blue, a mixture which is also known as _Brunswick Green_. Fine bright greens, they are suited to the ordinary purposes of mechanic painting, but are quite unfit for the artist's craft, chrome yellow reacting upon and ultimately destroying Prussian blue when mixed therewith. For the latter, cheap cobalts and ultramarines are preferably subst.i.tuted, although they do not yield greens of like power and intensity.

Under the names of English Green, Green Cinnabar, &c., 'new' green pigments have been from time to time introduced, which have turned out mixtures of Prussian blue and chromate of lead; not made, however, by compounding the two, but directly by processes similar to the following:--A mixed solution of the acetates of lead and iron is added to a mixed solution of the yellow prussiate and chromate of potash, the necessary acetate of iron being obtained by precipitating a solution of acetate of lead by sulphate of iron, and filtering the supernatant liquid. Or; to a solution of Prussian blue in oxalic acid, first chromate of potash is added, and then acetate of lead.

By the last process, superior and more permanent chrome greens may be produced, free from lead, by using chloride of barium or nitrate of bis.m.u.th in place of the acetate of lead. Chromate of baryta, or chromate of bis.m.u.th is then formed, neither of which acts on the Prussian blue.

It should be added that where the latter pigment is present, no green will serve for painting walls containing lime, as its action alters the tint of the Prussian blue.

186. HOOKER'S GREEN

is a compound of Prussian blue and gamboge, two pigments possessing a like degree of stability, and perfectly innocuous to each other. It is a mixture more durable and more transparent than chrome greens made with chromate of lead. There are two varieties in common use--No. 1, a light gra.s.s green, in which the yellow predominates; and No. 2, a deeper and more powerful green, with a larger amount of blue.

187. PRUSSIAN GREEN,

like the preceding, is composed of Prussian blue and gamboge; but contains a very great excess of the former, and is therefore a bluish-green of the utmost depth and transparency, verging on black in its deep washes. Yellow ochre may be employed instead of gamboge, but is not so eligible.

A true Prussian green, which has been recommended as a pigment, can be produced as a simple original colour, with a base wholly of iron. It is got by partially decomposing the yellow oxalate of protoxide of iron with red prussiate of potash. We have made this green and given it a fair trial, but our verdict is decidedly against it. In colour it is far from being equal to a good compound of Prussian blue and gamboge, and it a.s.sumes a dirty buff-yellow on exposure to light and air, the film of blue on the oxalate more or less disappearing.