This section is from the book "Chromatography; Or, A Treatise On Colours And Pigments, And Of Their Powers In Painting", by George Field. Also available from Amazon: Chromatography, or A Treatise on Colours and Pigments, and of Their Powers in Painting.
"Parthenius thinks in Reynolds' steps he treads, And every day a different palette spreads; Now bright in vegetable bloom he glows, His white - the lily, and his red - the rose; But soon aghast, amid his transient hues, The ghost of his departed picture views: Now burning minerals, fossils, bricks, and bones, He seeks more durable in dusky tones, And triumphs in such permanence of dye, That all seems fix'd, which time would wish to fly." Shee.
In the preceding discussion colours are distinguished into inherent and transient, the latter of which, as their name implies, are essentially fugacious; our present argument is, therefore, limited to the permanence and mutability of the inherent colours of pigments, as those which are principally important to the artist.
All durability of colour is relative, because all material substances are changeable and in perpetual action and reaction; there is, therefore, no pigment so permanent as that nothing will change its colour, nor any colour so fugitive as not to last under some favouring circumstances; while time of short or long continuance has generally the immediate effect thereon of fire more or less intense, according to the laws of combustion and chemical agency. It is, indeed, some sort of criterion of the durability and changes of colour in pigments, that time and fire produce similar effects thereon: thus if fire deepen any colour, so will time; if it cool or warm it, so will time; if it vary it to other hues, so will time; and if it consume or destroy a colour altogether, so also will time ultimately; but the power of time varies extremely with regard to the period in which it produces those effects which are instantly accomplished by fire: fire is also a violent test, and subject to many exceptions.
That there is no absolute but only relative durability of colour may be proved from the most celebrated pigments; - thus the colour of ultramarine, which, under the ordinary circumstances of a picture, will endure a hundred centuries, and pass through naked fire uninjured, is presently destroyed by the juice of a lemon or other acid. So again the carmine of cochineal, which is very fugitive and changeable, will, when secluded from light, air, and oxygen, continue half a century or more; while the fire or time which deepens the first colour will dissipate the latter altogether. Again, there have been works of art in which the white of lead has retained its freshness for ages in a pure atmosphere, and yet it has then been changed to blackness after a few days', or even hours' exposure to a foul air. These and other affections of colours will he instanced throughout when we come to the consideration of individual pigments; not for the purpose of destroying the artist's confidence in his materials, but as a caution and guide to the availing himself of their powers properly.
It is therefore the lasting under the ordinary conditions of painting, and the common circumstances to which works of art are exposed, which entitle a colour or pigment to the character of permanence; and it is the not-so-enduring which subjects it properly to the opposite character of fugacity; while it may obtain a false repute for either, by accidental preservation or destruction under unusually favourable or fatal circumstances, all of which has been frequently witnessed.
It has been supposed by some that colours vitrified by intense heat are durable when levigated for painting in oil or water. Had this been true, the artist need not have looked farther for the furnishing of his palette than to a supply of well-burnt and levigated enamel colours; - but though these colours for the most part stand well when fluxed on glass, or in the glazing of enamel, porcelain, and pottery, they are almost without exception subject to the most serious changes when ground to the degree of fineness necessary to render them applicable to oil or water painting, and become liable to all the chemical changes and affinities of the substances which compose them. These remarks apply also to those who ascribe permanence to native pigments only, such as the coloured earths and metallic ores.
Others, with some reason, have imagined that when pigments are locked up in varnishes and oils, they are safe from all possibility of change; and there would be much more truth in this position if we had an impenetrable varnish, - and even then it would not hold with respect to the action of light, however well it might exclude the influences of air and moisture: but, in truth, varnishes and oils themselves yield to changes of temperature, to the action of a humid atmosphere, and to other chemical influences: their protection of colour from change is therefore far from perfect; and the above opinion of them is only in some degree true, but ought not to render the artist inattentive to the durability of his colours in themselves. Reynolds, unfortunately, entertained this opinion of the preserving power of varnishes; and, although the practice of his own palette was exceedingly empirical, he was an utter condemner of such practice in others.*
On the other hand, want of attention to the unceasing mutability of all chemical substances, and 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 they have been improperly mixed and applied. It is thus that the best pigments have sometimes suffered in reputation under the injudicious processes of the painter, and that these effects and results have not been uniform in consequence of a desultory practice. If a pigment be not extremely permanent, diluting it 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, and by distribution, in glazing or lackering, of colours upon the lights downward, or scumbling colours upon the shades upward; or, according to a mixed mode, in which transparent and opaque pigments are combined, as umbre and lake - much employed by the Venetian painters.
* Northcote's " Memoirs of Sir J. R." - Supplement p. 80.