Field's Chromatography

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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.


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