The most natural or fit distribution of vehicles is into those of water, oils, and their mediums or compounds; under which heads we proceed to regard them, and the various substances employed as additions, according to the variety of practice.

As the action of aqueous liquids, and their solvents upon colours, is stronger and more immediate than that of oils and varnishes, it is of great importance to the water-colour painter that he should attend to the pureness of his water. He ought to use no other than distilled water; or, wanting this, he should use rain-water fittered, which is next in purity to distilled water. In all hard and impure waters, colours are disposed to separate and curdle, so that it is often impossible a clear flowing wash, or gradation of colour, should be obtained with them. Solution of gums, ox-gall, etc. correct, without entirely overcoming these defects of the water; but they are often inconvenient, if not injurious: we recommend, therefore, to colourraen to keep distilled water ready for artists' use; or the latter may, if he pleases, procure it of the chemists, or use in its stead the distilled water of roses, or lavender, etc. which have no injurious effect upon colours, and recommend themselves by their agreeable scents: but then they must be the really distilled waters, and not the compounds sold as perfumes under their names.

Water, as a vehicle compared with oil, is of simple and easy use, drying readily, and being subject to little alteration of colour or effect subsequently; for notwithstanding oils and varnishes are less chemically active upon colours than aqueous fluids are, those vehicles of the oil-painter subject him to all the perplexities of their bad drying, change of colour, blooming, and cracking, - to habits varying with a variety of pigments, and to the contrariety of qualities, by which they are required to unite tenuity with strength, and to be fluid without flowing, etc.; to provide for and reconcile all which has continually exercised the ingenuity of the artist.

Mucilages. Gum, or some mucilaginous substance, is a necessary addition to water to give pigments their requisite cohesion, and to attach the colours to the paper or ground on which they are applied, as well as to give them the property of bearing out to the eye, according to the intention of the artist; upon which, and upon the pigments used, depend the proportions of gum to be employed, gum being a constituent of some pigments, while others are of textures to require it in considerable quantity to give them proper tenacity, - qualities we have adverted to in speaking of individual pigments: as a general rule, however, the proportion of gum employed with a colour should be sufficient to prevent its abrasion, but not so much as to occasion its scaling or cracking, both of which are easily determined by trial upon paper.

Senegal. Of Gums, Senegal is the strongest and best suited to dark colours, being of a brown hue; but the light-coloured pieces may be employed for the more delicate pigments. All gums contain an acid very unfavourable to their preservation in a fluid state; which acid requires, therefore, to be neutralized by the addition of some alkaline substance, of which we have found the carbonate of ammonia, being volatile, to be the best; a small portion of which being shook into the dissolved gum will purify it by precipitating all its foulness, and preserve it a very long time for use, and very much improve the working of colours without occasion for gall: the gum will rarely require more than one scruple of the powdered carbonate to an ounce of the gum dissolved by maceration in two or three ounces of cold water. Solution of borax will answer the same purpose, but less eligibly.

Gum Arabic is in general clearer and whiter than Senegal, and hence is better adapted to the brighter and more delicate colours. It should be picked and purified by solution in cold water, straining, and decanting; and should be used fresh, or preserved by addition of alcohol, or by ammonia in the manner already described.

Ammoniac, or Gum Ammoniac, is a gum-resin, soluble in spirit and in water, in the latter of which it forms a milky fluid that dries transparent: it has many properties which render it useful in water-painting, and is, we have found, superior to the gums in forming some colours into cakes, causing them to work off. It is avoided by insects, is very tenacious, and affords a middle vehicle between oil and water, with some of the advantages of both. It contributes also, in the manner of a varnish, to protect the more fugitive colours over which it may be glazed, or with which it may be mixed, and on this account it is eligible in water-painting.

Tragacanth is a strong colourless gum, soluble in hot water, and of excellent use when colours are required to lie flat, or not bear out with gloss, and also when a gelatinous texture of the vehicle is of use to preserve the touch of the pencil and prevent the flowing of some colours; or to fix drawings executed with the black-lead pencil; for all which purposes, also, solution of isinglass is available, and of greater power; as are also starch, as prepared by the laundress, and the water in which rice has been boiled, used as a vehicle by Chinese artists.

Isinglass. A most excellent mucilage for water-painting may be made by diluting gradually clear size of isinglass with boiling water, till, on becoming cold, it just flows and loses its gelatinous texture: in this liquid is then to be dissolved by gentle heat as much colourless gum Senegal, or Arabic, as it will conveniently take up.

The late Mr. Robertson, of Worton, employed isinglass in water-painting with the full powers of oil-painting, when varnished. His vehicle, for which the Society of Arts voted him a gold medal, may be prepared by suffering shreds of isinglass to imbibe cold water till thoroughly soft, and then dissolving them in boiling alcohol, in such proportions as will just produce a fluid compound when cold.

The Society of Arts, etc, have also presented a medal to Mr. J. Hammond Jones, for a process in miniature-painting, in which he employed as a vehicle a cold saturated solution of borax in water, in one quart of which he dissolved a quarter of an ounce of gum tragacanth, which he found dried sufficiently firm to allow tints to be repeatedly laid one over another without moving or washing up.

Albumen, etc. Albumen, or white of egg, has been employed as an addition to water vehicles; and, for the common purposes of distemper paintking, milk and the serum of blood have been proposed, but are not adapted to fine art.

To the employment of the glare, or white of egg, by the early masters in oil, and also of the yolk, as directed by Vasari, is probably owing the preservation of their lakes and other colours, and the purity of their whites, which are most beautiful and remarkable in the works of the Van Eycks and Rachael Rych; and, as both these substances have tenacity and texture equalling and much resembling those of oils, and superior to gums, it is apparent that the entire egg, well beat and strained, would also afford a practicable vehicle. The glovers also use yolk of egg for their delicate colouring of kid leather. The same substance has been very successfully employed by our skilful friend Mr. Clover, for sketching in body-colours, in the manner, and with the entire effect, of oil; which sketches, being varnished, have retained their original purity of hue, more especially in the whites, and flexibility of texture without a crack, after many years in a London atmosphere.

One great advantage of an egg vehicle would evidently be, that terrene whites of the purest colour might be employed, instead of lead, in an oil medium; such as barytic and the true pearl whites, he.

Borax, Gall, Sugar, etc. The unnecessary use of sugar in water-colours should be avoided, as it is disposed to acid fermentation with gum, and is attractive of damp from the atmosphere, and of flies and other insects; as are also honey and other saccharine substances. Animal gall is necessary only to attach the colours to the ground when it rejects them, or they work greasy, as is often the case on ivory and very smooth vellum or polished substances, or over certain pigments. Borax, which is mildly alkaline, answers the same purpose; as friction with India-rubber will also. Spirit of wine, or alcohol, is principally of use in water-vehicles, as an antiseptic, to preserve them from frost, mildew, and putrescence.