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.
"How many fondly waste the studious hour To seek in process what they want in power; Till, all in gums engross'd, macgilps, and oils, The painter sinks amid the chemist's toils."
Since colours and pigments are liable to material influence, and changes of effect, from the materials employed in painting for tempering, combining, distributing, and securing them on their grounds in the various modes of the art, the powers and properties of vehicles and varnishes are of hardly less importance than those of colours themselves; they are, therefore, an essential branch of our subject, and an inquiry of interminable interest among artists. Vehicles, which term is borrowed from pharmacy, are, indeed, among the chief materials and indispensable means of painting, and give names to its principal modes or genera, under the titles of painting in water, in oil, in varnish, etc.: we will consider them, therefore, in each of these respects.
Though originally few and simple, vehicles have been extremely diversified by composition and addition, suited to the various purposes and fancies of artists, so as to have become a subject of no mean extent and intricacy; to explicate which perfectly is as far from our hope as our intention, which is to treat of it in a general way, with such hints and remarks as have sprung from our own observation and experience, and may tend to improvement in practice.
Speculation, and enquiry into the practices of the old masters and various schools of painting concerning the secret mixtures they employed as vehicles, are at once uncertain and fruitless in these times, when the properties of the substances employed are so much better understood. The questions for the artist now are, what substances are the fittest to be employed? and what mixtures are best authorized by experience and chemical science for producing the effects he requires! and to this we shall direct our attention in reference to the various modes of practice.
It is observable that the colours of pigments bear out with effects differing according to the liquids with which they are combined, and the substances those liquids hold in solution, which in some instances obscure or depress, and in others enliven or exalt the colours; in the first case by the tinge and opacity of the fluid, and in the latter, by its colourless transparency, and sometimes also much more so by a refractive power; as in varnishes made of pure resinous substances, which have a very evident and peculiarly exalting effect upon colours, that continues when they are dry; because resins form a glossy transparent cement, while the media, formed by expressed oils, become horny, or semi-opaque. And this principle applies also to aqueous and spirituous vehicles in water-painting, according to the nature of the gums, or other substances they may hold in solution.