Read Ebook: Field's Chromatography or Treatise on Colours and Pigments as Used by Artists by Field George Salter Thomas W Editor

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It is, therefore, the lasting under the usual conditions of painting, and the common circumstances to which works of art are exposed, that entitles a colour to the character of permanency; and it is the not-so-enduring which attaches to it rightly the opposite character of evanescence: while a pigment may obtain a false repute for either, by accidental preservation or destruction under unusually favourable or fatal circumstances.

Many have imagined that colours vitrified by intense heat are consequently durable when levigated for painting in oil or water. Had this been the case, the artist need not have looked farther for the furnishing of his palette than to a supply of well-burnt and levigated enamel pigments. But though such colours for the most part stand well when fluxed on glass, or in the glazing of enamel, they are nearly, without exception, subject to the most serious changes when ground to the degree of fineness necessary to their application as pigments, and become liable to all the chemical changes and affinities of the substances which compose them. These remarks even apply in a measure to native products, such as coloured earths and metallic ores.

Others have not unreasonably supposed that when pigments are locked up in varnishes and oils, they are safe from all possibility of change. The assumption would be more warranted if we had an impenetrable varnish--and even that would not resist the action of light, however well it might exclude the influence of air and moisture. But, in fact, varnishes and oils themselves yield to changes of temperature, to the action of a humid atmosphere, and to other influences: their protection of colour from change is therefore far from perfect.

Want of attention to the unceasing mutability of all chemical substances, as well as to their reciprocal actions, has occasioned those changes of colour to be ascribed to fugitiveness of the pigment, which belong to the affinities of other substances with which it has been improperly mixed and applied. It is thus that the best pigments have suffered in reputation under the injudicious processes of the painter; although, owing to a desultory practice, the effects and results have not been uniform. If a colour be not extremely permanent, dilution will render it in some measure more weak and fugitive; and this occurs in several ways--by a too free use of the vehicle; by complex mixture in the formation of tints; by distribution, in glazing or lackering, of colours upon the lights downward, or scumbling colours upon the shades upward; or by a mixed mode very common among the Venetian painters, in which opaque pigments are combined, as umber and lake.

The fugitive colours do less injury in the shadows than in the lights of a picture, because they are employed pure, and in greater body in shadows, and are therefore less liable to decay by the action of light, and by mixture. Through partially fading, moreover, they balance any tendency to darken, to which the dead colouring of earthy and metallic pigments is disposed.

The foregoing circumstances, added to the variableness of pigments by nature, preparation, and sophistication, have often rendered their effects equivocal, and their powers questionable. These considerations enforce the expediency of using colours as pure and free from unnecessary mixture as possible; for simplicity of composition and management is equally a maxim of good mechanism, good chemistry, and good colouring. Accordingly, in respect to the latter, Sir Joshua Reynolds remarks, "Two colours mixed together will not preserve the brightness of either of them single, nor will three be as bright as two: of this observation, simple as it is, an artist who wishes to colour bright will know the value."

There prevail, notwithstanding, two principles of practice on the palette, opposed to each other--the one, simple; the other, multiple. The first is that of having as few pigments as possible; and consists, when carried to the extreme, in employing the three primary colours only. The second is that of having a number of pigments; and consists, also when carried to the extreme, of employing as many, if possible, as there are hues and shades of colour.

The superiority of Rubens and the Flemings, and of Titian and the Venetian school, in colouring and effect, is due in a considerable degree to their sketching their designs in colours experimentally with a full palette. This practice, as derived from Reynolds, is common with the best masters of our own school, who, in executing their works, resort also to nature, with an improved knowledge of colours and colouring. Such attention to colouring and effect, from the first study and ground of a picture to the finishing, contributes a beauty to the painting no superinduced colouring can accomplish.

Many, too, cannot safely come into contact with iron, or ferruginous pigments; especially the yellows of arsenic, the lakes of cochineal, and the blues and greens of copper. With these an iron palette knife is best avoided, one of ivory or horn being used instead. The latter, indeed, is preferable in all cases, several pigments being slightly affected by iron, cadmium yellow among the number.

Time produces in many cases a mellow and harmonious change in pictures, but occasionally alterations altogether unfavourable. To ensure the former and prevent the latter, the attention of the artist in the course of his colouring should be to the employment of such pigments and colours as are prone to adapt themselves, in changing, to the intended key of his colouring, and the right effect of his picture. Thus, if he design a cool effect, ultramarine has a tendency through time to predominate and aid the natural key of blue. He will, therefore, compromise the permanence of this effect, if in such case he employ a declining or changeable blue, or if he introduce such reds and yellows as have a tendency to warmth or foxiness, by which the colouring of many pictures has been destroyed. In a glowing or warm key, the case is in some measure reversed--not wholly so, for it is observable that those pictures have best preserved their colouring and harmony in which the blue has been most lasting, by the pigment counteracting the change of colour in the vehicle, and that suffusion of dusky yellow which time is wont to bestow upon pictures even of the best complexion.

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. So the dazzling scarlet of iodine and mercury must yield the palm of excellence to the more sober vermilion, being a chameleon colour, subject to the most sudden and opposite changes. And the blues of cobalt, as always tending to greenness and obscurity, cannot rank beside ultramarine.

Perhaps one reason why freshly introduced pigments have not as fair a chance as they are entitled to, is due to the fashion which prevails of exclaiming against the fugacity of modern colours. If their detractors would confine themselves to certain colours, there could be no denial; but to assert, as is often done, that the cause of modern pictures not standing is owing to modern pigments generally, is unjust. It is not the materials which should be blamed, but those who use them. The fact is, that the artist's knowledge has not increased in proportion to the greater variety of colours at his command. In the early periods of art, when the palette was chiefly confined to native pigments, the painter could not very well go wrong. Now-a-days but too many, wanting the skill of the old masters, seek to make amends for it by brilliancy of colouring: with imperfect knowledge of their materials the result is obvious. The palette, we admit, wants weeding; not only of the bad new colours, but of the bad old colours. This, however, must be a work of time, and depend, not upon the colourman--for where there is a demand there will be a supply--but upon the artists themselves. To this end an increased acquaintance with the properties of pigments is required, whereby they may be able to choose the fast from the fugitive. It may be fairly assumed that the painter will be assisted in his task by the progress of chemical science, which will doubtless add from time to time to the list of stable pigments. We have heard it remarked that there are too many colours already--to which we reply, there are not too many good colours, and scarcely can be. The more crowded the palette is with reliable pigments, the more likely are the worthless to be pushed from their places. In our opinion, there is ample room for fresh colours, provided they be durable; and we have as little sympathy with the stereotyped cry of there being too many, as with the fashionable unbelief in modern pigments. Certainly, the artist who seeks for permanence among the whites, reds, or blues, will not be troubled with a superfluity. Certainly, too, colours are as good as ever they were, and better--better made, better ground, better prepared for use. But, fast and fugitive, pigments are more numerous, and for that reason need more careful selection.

ON THE GENERAL QUALITIES OF PIGMENTS.

It must be observed that no pigment possesses all the foregoing qualifications in perfection, some being naturally at variance or opposed; nor is there any, perhaps, that cannot boast excellence in one or more of them.

It is not always that ill drying is to be attributed to the pigments or vehicles, the states of the weather and atmosphere have great influence thereon. The direct rays of the sun are powerfully active in rendering oils and colours siccative, and were probably resorted to before dryers were--not always wisely--added to oils, particularly in the warm climate of Italy. The ground may also advance or retard drying, because some pigments united by mixing or glazing, become either more or less siccative by their conjunction. Many other accidental circumstances may likewise affect drying; and among these none is to be more guarded against by the artist than the presence of soap and alkali, too often left in the washing of his brushes, and which, besides other bad results, decompose and are decomposed by acetate of lead and most siccatives. In such cases desiccation is retarded, streaks and patches are formed on the painting, and the odium of ill drying falls upon some unlucky pigment. To free brushes from this disadvantage, they should be cleansed with linseed oil and turpentine. Dryers should be added to colours only at the time of using them, because they exercise their drying property while chemically combining with the oils employed, during which the latter become thick or fatten. Too much of the siccative will, as before noticed, often retard drying.

The various affinities of pigments occasion each to have its more or less appropriate dryer; and it would be a matter of useful experience if the habits of every colour in this respect were ascertained. It is probable that siccatives of less power generally than the compounds of lead and copper might come into use in particular cases, such as the oxides of manganese, to which umber and the Cappagh browns owe their drying quality.

ON COLOURS AND PIGMENTS INDIVIDUALLY.

ON COLOURS AND PIGMENTS INDIVIDUALLY.

Having briefly discussed the relations and attributes of colours and pigments generally, we come to their powers and properties individually--a subject pregnant with materials and of unlimited connexions, every substance in nature and art possessing colour, the first quality of pigments.

The attention of the artist to the individual powers of pigments, although it may be of less concern than the attention to general effect in colouring, is by no means less necessary in practice. For he who would excel in colouring must study it from several points of view, in respect to the whole and the parts of a picture, as regards mind and body, and concerning itself alone. To this end, is needed a knowledge of his pigments individually.

If nature has arrayed herself in all the colours of the rainbow, she has not been niggardly in offering man the materials wherewith to copy them. The mineral, animal, vegetable kingdom--each helps him to realize, however faintly, her many manifold beauties: to give some idea, however slight, of that glorious flood of colour, which light lets loose upon the world. Metal, ore, earth, stone; root, plant, flower, fruit; beast, fish, insect--in turn aid the arduous task. The painter's box is a very museum of curiosities, from every part of the universe. For it, the mines yield their treasures, as well as the depths of the sea: to it come Arab camel, and English ox, cuttle-fish and crawling coccus: in it the Indian indigo lies next the madder of France, and the gaudy vermilion of China brightens the mummy of Egypt. Varied, indeed, are the sources whence we derive our pigments; and if they still leave much to desire, improvement is clearly manifest. Slowly but surely, year by year, we are advancing. With the growth of science, the exhaustless stores of creation, will there at last be attained--step by step, though it be--that summit of the artist's hopes, a perfect palette?

ON THE NEUTRAL, WHITE.

The term "colour" is equivocal when applied to the neutrals, yet the artist is bound to consider them as colours; for a thing cannot but be that of which it is composed, and neutrals are composed of, or comprehend, all colours.

Locally, white is the most advancing of all colours in a picture, and produces the effect of throwing others back in different degrees, according to their specific retiring and advancing powers. These latter, however, are not absolute qualities of colours, but depend on the relations of light and shade, which are variously appropriate to all colours. Hence it is that a white object rightly adapted, appears to detach, distribute, and put in keeping; as well as to give relief, decision, distinctness, and distance to every thing around it: hence, too, the use and requirement of a white or light object, in each separate group of a composition. White itself is advanced or brought forward, unless indeed white surround a dark object, in which case they retire together. In mixture, white communicates these properties to its tints, and harmonizes in conjunction with, or in opposition to all colours; but lies nearest in series to yellow, and remotest from blue, of which, next to black, it is the most thorough contrast. It is correlative with black, which is the opposite extreme of neutrality.

Perfect white is opaque, and perfect black transparent; hence when added to black in minute proportion, white gives it solidity; and from a like small proportion of black combined with white, the latter acquires locality as a colour, and better preserves its hue in painting. Both white and black communicate these properties to other colours, in proportion to their lightness or depth; while they cool each other in mixture, and equally contrast each other when opposed. These extremes of the chromatic scale are each in its way most easily denied, as green, the mean of the scale, is the greatest defiler of all colours. Rubens regarded white as the nourishment of light, and the poison of shadow.

In a picture, white should not be merely glittering or brilliant, but tender as well as bright. The eye should seek it for rest, brilliant though it may be; and feel it as a space of strange heavenly paleness in the midst of the flushing of the colours. This effect can only be reached by general depth of middle tint, by the perfect absence of any white, save where it is needed, and by keeping the white itself subdued by grey, except at a few points of chief lustre.

White, as a pigment, is of more extensive use than any other colour in oil painting and fresco, owing to its local quality, its representing light, and its entering into composition with all colours in the formation of tints. The old masters have been supposed by some to possess whites superior to our own, but this may be questioned. The pureness of whites in some celebrated old pictures is rather to be attributed to a proper method of using, careful preservation of the work, and in many instances to the introduction of ultramarine or a permanent cold colour into the white--such as plumbago--helped also by judicious contrast.

Notwithstanding white pigments are tolerably numerous, a thoroughly unexceptionable white is still a desideratum--one combining the perfect opacity or body of white lead with the perfect permanency of zinc white. The nearest approach to it that has yet been made, is Chinese white, which possesses in a great measure the property of the former, and, being a preparation of zinc, has wholly that of the latter. Unfortunately Chinese white is a water-colour pigment only, not retaining its several advantages, stability excepted, when employed in oil.

Constant white is a sulphate of baryta, found native and known under the name of heavy-spar, or prepared artificially by adding sulphuric acid, or a soluble sulphate, to a solution of a barytic salt. In the first mode, if the white be not well purified from free acid, it is apt to act injuriously on some pigments. Sulphate of baryta is often used for the purpose of adulterating white lead, the native salt being ground to fine powder, and washed with dilute sulphuric acid, by which its colour is improved, and a little oxide of iron probably dissolved out. Whether native or artificial, the compound is quite unaffected by impure air, and is not poisonous.

LEAD WHITES

The heaviest and whitest of these are the best, and in point of colour and body, are superior to all other whites. When pure and properly applied in oil and varnish, they are comparatively safe and durable, drying well without addition; but excess of oil discolours them, and in water-painting they are changeable even to blackness. Upon all vegetable lakes, except those of madder, they have a destructive effect; and are injurious to gamboge, as well as to those almost obsolete pigments, red and orange leads, king's and patent yellow, massicot, and orpiment. With ultramarine, however, red and orange vermilions, yellow and orange chromes, yellow and orange and red cadmiums, aureolin, the ochres, viridian and other oxides of chromium, Indian red &c., they compound with little or no injury. Lead colours must not be employed in water-colour or crayon painting, distemper, or fresco. The whites of lead are carbonates of that metal, with two exceptions:--Flemish white or the sulphate, and Pattison's white or the oxychloride. In using all pigments of which lead is the basis, cleanliness is essential to health.

White lead, by which we must be understood to mean the carbonate, always contains when commercially prepared a certain proportion of hydrated oxide. The less of the latter there is present, the better does the white cover, and the less liable is it to turn brown. The products formed by precipitation have proved to be inferior in body: otherwise, pure mono-carbonate of lead-oxide, obtained by mixing solutions of carbonate of potash and a lead-salt, might be best adapted for a pigment. However, such a carbonate has been lately produced by Mr. Spence's process of passing carbonic acid gas into a caustic soda or potash solution of lead, and for this white an opacity is claimed equal to that of the ordinary compound.

Great as is the opacity of white lead, it is apt to lose that property in some measure in course of time, and become more or less transparent. If, over a series of dry oil-colour rubs of varied hues, there were brushed sufficient white lead paint to utterly obscure them, after some years those rubs would indistinctly appear, and by degrees become more and more visible, until at last their forms--if not their very colours--could be recognised. From this it would seem that white lead must slowly but surely part with some of its carbonic acid, and be at length converted into dicarbonate, a compound possessing less carbonic acid, and less coating power.

Impure air, or sulphuretted hydrogen, browns or blackens white lead, converting it partially or wholly into sulphide. It would appear from the recent investigations of Dr. D. S. Price, that white lead is less liable to be thus affected, when the pictures in which it is used are exposed to a strong light; also, that when such pictures have so suffered, a like exposure will restore them. We have ourselves noticed the rapidity with which an oil rub of white lead that has been damaged by foul gas, regains its former whiteness when submitted to air and sunshine. The action of drying oils has been likewise proved to be very powerful upon sulphide of lead, an exposure to light for a few days only being sufficient to change a surface of it, coated with a thin layer of boiled linseed oil, into a white one. Probably, these agents may have a similar effect upon other pigments injured by sulphuretted hydrogen, and many of the colours in paintings may be restored by treating them with boiled linseed oil, and submitting them to a strong light. That the result is due to oxidation, there can be no doubt. Indeed, the eminent French chemist, M. Th?nard, was consulted some years back upon the means of bringing to their original whiteness the black spots which had formed upon a valuable drawing, by the changing of the white lead, and employed for that purpose oxygenated water. He had ascertained its power of converting the black sulphide of lead into the white sulphate, and, by touching the spots with a brush dipped in the fluid, soon succeeded in restoring the drawing to its primitive state. Here, again, the use of the agent might doubtless be extended to other colours, to which foul air is inimical.

In oil painting white lead is essential in the ground, in dead colouring, in the formation of tints of all colours, and in scumbling, either alone or mixed with other pigments. It is also the best local white, when neutralized with ultramarine or black; and it is the true representative of light, when warmed with Naples yellow, or orange vermilion or cadmium, or with a mixture of the yellow and either of the orange pigments, according to the light.

Ordinary white lead is often mixed with considerable quantities of heavy spar, gypsum, or chalk. These injure it in body and brightness, dispose it to dry more slowly, keep its place less firmly, and discolour the oil with which it is applied, as well as prevent it dissolving completely in boiling dilute potash-ley, a test by which pure white lead may be known.

The adulteration of pigments, which we have in some instances found practised to a large extent abroad, is comparatively unfrequent in our own country, so far at least as regards the superior class of colours employed by artists. As a rule, such colours when manufactured in England may be fairly assumed to be genuine; and certainly the respectable colourmen of the present day are not in the habit of sophisticating them. We must bear testimony, indeed, to the zeal with which they purvey, regardless of necessary expense, the choicest and most perfect materials. This should be a matter of congratulation to the painter, who must of necessity rely on the faith and honesty of his colour-dealer; for if he were ever so good a chemist, it would be impossible for him to analyse each pigment before proceeding to use it. The fault must rest with himself, therefore, if, through a mistaken economy, he do not frequent the best houses and pay the best prices. Of a surety, the colours of the artist are not among those things in which quality can, or should, be sacrificed to cheapness.

Is an exceedingly white precipitate from any solution of lead by sulphuric acid, much resembling the blanc d'argent. It is inferior, however, both in body and permanence to the ordinary carbonate. Hence, white lead which has more or less been converted by sulphuretted hydrogen into sulphide, and again been converted into sulphate by oxidation, with a view to restoring its colour, becomes peculiarly liable to the influence of impure air.

The best of these do not essentially differ from each other, nor from the white leads of other manufactories. The latter variety, being prepared from flake white, is usually the greyer of the two.

Is a mixture of chloride and oxide of lead, formed by precipitating a solution of chloride of lead with soda, potash, lime, or baryta, in the caustic or hydrated state. It would appear that when the oxychloride is used as a paint, the oxide contained in it gives rise to an oleate of lead, and, in consequence of this saponaceous matter, is capable of spreading over an extended surface. The product has been described as possessing properties which are superior to those of white lead, inasmuch as it does not so readily blacken as the latter body. Dr. Ure, however, found that water removes the chloride of lead from the paint compounded of this article, and, consequently, that it is not so effectual as the carbonate. As an artist's pigment, a partially soluble compound of lead can decidedly not be eligible.

Is of the purest white colour, and differs only from blanc d'argent in the warm flesh tint of the external surface of the large square masses in which it is commonly prepared.

Besides the foregoing, there are other white leads, generally foreign, cheaper, and adulterated. Many of these are mixed with a small quantity of charcoal, indigo, or Prussian blue, so that the dead yellowish shade which they present may be enlivened to a brighter hue. Among them may be named--

A French variety, not necessarily, but not unfrequently, mixed with different chalky earths in various proportions; and the following Belgian kinds:

Containing three fourths of sulphate of baryta.

A mixture of two parts of heavy spar and one of the plumbous compound.

Differing from the rest in being unadulterated.

Composed of heavy spar and the carbonate in equal proportions.

ZINC WHITES.

The introduction, in 1834, of this peculiar preparation of oxide of zinc has proved an incalculable boon to water-colour painters, who formerly had no white which combined perfect permanency with good body in working. Its invention obviated the necessity for using white lead, a pigment which, though it may be employed with comparative safety in oil, is quite unfitted for water. Since the period of its production, Chinese white has been generally preferred by water-colour artists, as being the most eligible in their peculiar department. Previous to that period, the complaints of whites changing were of constant occurrence; but in no instance has any picture, in which this white has been used, suffered from its employment. To the colour of oxide of zinc, sulphuretted hydrogen is altogether harmless; sulphide of zinc being itself white. The variety under notice works and washes well, possesses no pasty or clogging properties, and is prepared beautifully white. Moreover, it has the desirable quality of dense body; so much so, that, as the painter works, his effects remain unaltered by the drying of the colour. It may likewise be safely mixed with all other pigments, the following blending very satisfactorily with the white for opaque lights--cadmium yellow, orange, and red; gamboge; aureolin; yellow ochre; vermilion; and light red. Without the artistic drawbacks of constant white or the chemical defects of white lead, and retaining the advantages of both, Chinese white cannot but be considered as a most important addition. It is a matter of regret that this pigment is not equally efficacious in oil.

Is either the anhydrous oxide, the hydrate oxide, or hydrated basic carbonate of zinc. It varies in opacity and colour according to the mode of manufacture, and the purity of the compound, but may always be relied upon as permanent. The whiteness of the best samples rivals that of white lead, and it is not tarnished like the latter by sulphurous vapours. In opacity it never equals white lead, and might perhaps serve advantageously as a glaze over that pigment, either alone or compounded with other colours; as well as act as a medium of interposition between white lead and those colours which are injured by it, such as gamboge, crimson lake, &c. When duly and skilfully prepared the colour and body of this pigment are sufficient to qualify it for a general use upon the palette in oil: in water it has been superseded by Chinese white.

Occasionally, starch, chalk, white clay, and carbonate of baryta, are employed as adulterants; none of which, however, are inimical to stability.

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