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.
Many attempts have been made to unite the advantages of the two modes of painting - of water and oil - either by successive processes, or by the use of a vehicle of a compound or intermediate affinity to both of these fluids, and thence technically denominated a medium; a term otherwise properly applicable to every vehicle.
It has been an opinion of eminent judges in the art, that the Venetian painters - after a mode also ascribed to some of the great antient Greek artists - employed oils and varnishes only as preservatives and defences of their works, and not as vehicles of their colours, for which latter purpose they are supposed to have used water with proper additions; and there can be little doubt that the subsequent transition from fresco and distemper painting to oil painting was not sudden but progressive; and it is probable, if not certain, that the early painters in oil grounded and began their pictures in a size or water vehicle, in the manner of body-colour painting on Cartoons, or with a vehicle, analogous to our lac vehicle, in which borax was employed; and this opinion is supported by the fact that portions of their decayed pictures have been readily fluxed by fire into glass. Such a vehicle has long been used in India, and the Venetians had the whole commerce of the East, whence their painters might obtain their fine pigments and materials - Indian lakes, Chinese vermilion, ultramarine, Indian reds, called Venetian, lac, borax, naphtha, bitumens, balsams, etc. The Dutch and Flemish schools, to which similar practice has been attributed, had also in their time all the like advantages of the Venetian.
With regard to mediums, all the gelatinous substances before mentioned as additions to Mater vehicles may be combined with linseed and other oils, and such compounds may be employed as vehicles, and will keep their place as delivered by the pencil in painting. Indeed starch, as prepared by the laundress, has been lately recommended with high encomiums for this purpose. Nevertheless we regard these mixtures as both chemically and mechanically inferior to the combination of lac and borax, which is equally diflusible in water and in oil, and does not contract in drying, or render the painting penetrable by moisture as farinaceous and mucilaginous substances do, nor, in the end, dispose the work to crack. It has accordingly been proposed that artists should adopt the Indian process of painting, in which lac is rendered saponaceous and miscibte in water by the medium of borax; but against this process the foul colour and opacity of the vehicle have been heretofore justly objected. If, however, one part of borax be dissolved in twelve of boiling water, and the solution be added in equal, or other proportions, to white lac varnish, a perfectly transparent colourless liquid is formed, which diffuses freely in water, and may be used, with some difficulty, as a vehicle for painting instead of oil, and when dry, is not acted on or removable by water. Pictures wrought in such vehicle would dry readily, and, being varnished with the white lac varnish, would have a homogeneity of texture throughout, freshness of colouring, and permanence in every way equal to oil-painting; add to this, that as this lac vehicle is as freely miscible with oil as it is with water, it supplies a true medium, or connecting link between painting in water and oil, which probably may, in some ingenious hand, unite the advantages of both: yet, as the tenacity and adhesion of lac vehicles depend in working upon a higher temperature than is common to our climate, they will in general require artificial heat of the painting-room, except during the summer; and may hence be better suited to a climate like that of India. If the above lac vehicle be mixed with an equal portion of oil of turpentine, it will form a vehicle which dries gradually throughout without skinning, keeps its place and forms a fine impasto, which becomes ultimately hard as stone; at the same time it preserves its colour and those of the pigments employed, bringing and keeping them out with all their force and transparency.*
By the above means, mastic and other soft resins may be rendered miscible in water, and even oils and bees'-wax may be introduced therein. These have the disadvantage, however, of being opaque, although in drying they become transparent.
* More than fifteen years ago we communicated these preparations to the late Peter Rainier, Esq., who agreeably deluded a life of leisure in seeking the medium of the old painters and similar researches; and we have been lately favoured with some notes on the subject by a reverend friend of his, a practically eminent amateur, who states that, " Mr. It. made bora into a glass, then very finely levigated it and mixed it in equal proportions with the oil. I remarked to him that, if it were the true medium it might be used with water. We tried it, and could dip the brush, after the paint had been stirred with it, in water. 1 have had some borax prepared, and used it in every way, anil find it admirable in the texture it gives - the enrichment of the colours, and facility of use. In the mending of old pictures I consider it invaluable, for you may use very little oil with it; match colour with it and use water, and it will, I believe, become as hard as iron." Others have employed soap and alkalis for the like purpose, and considered the compound as the true Venetian process: but these are less eligible than the borax.
The mode of encaustic painting, invented by Miss Greenland (afterwards Mrs. Hooker), published in the Transactions of the .Society of Arts, etc. for 1792 and 1807, which was an improvement upon the method of Count Caylus, was performed with a vehicle of this kind, which may be prepared by dissolving four and a half ounces of gum Arabia in eight ounces of pure water in a glazed vessel, to which seven ounces of powdered mastic are to be added, and the whole then stirred over a moderate fire till combined in an opaque uniform paste; five ounces of white wax are then to be added, and stirred till melted and beginning to boil, when the vessel should be removed from the fire, and sixteen ounces more of pure cold water gradually stirred into the mixture, which then will form a cream-like composition, to be kept in a bottle for use.