The manufacturing processes of the varnishes now generally used have been detailed in the Transactions of the Society of Arts, &c., Vol. XLIX. But with regard to the recipes for compounding varnishes, &c., superabounding in antient and modern treatises, however flatteringly recommended, there are few elegible or of practical utility, and yet fewer justifiable to art and good chemistry by the simplicity upon which certainty of effect depends, being in general quite of the class of recipes and formulæ of the old cookery books and dispensatories.

CHAPTER XXIV.

ON GROUNDS.

The last thing in the order of our analysis is the ground and basis on which colours, pigments, and vehicles, are applied in painting; and as the basis of fresco-painting is plaster, and that of watercolour painting is principally paper, the subject of grounds is chiefly of consideration with respect to painting in oil, in which mode a great variety of grounds have been employed, which have afforded a subject of wide speculation and experiment,—of many hopes and many failures, while the charm of Venetian art has been nearly as fruitful in exciting the invention of grounds as of vehicles.

The subject of grounds belongs to our inquiry only so far as regards their influence upon colours, and needs no very elaborate consideration here. Among the various bases upon which grounds have been laid are the metals, stone, slate, plaster, woods, card, vellum, and cloths, in all their variety. The qualities requisite to a perfect basis are durability, infrangibility, and inflexibility, which neither of these substances comprise in perfection. Metals are durable and infrangible in the highest degree; but they expand and contract by the mere alter

ations of temperature, and are, on this account, subject to detach or throw off portions of the ground, and to craze the painting and varnish. Linen cloths, parchment, and paper bases, are infrangible and durable in a high degree, but very flexible, which is remedied in a measure by straining and stretching; they become, therefore, variously eligible bases. Wood comprises all the qualities of a good basis in a medial degree, and hence, upon the whole, panel affords the best basis for small works. For works of a moderate size, in which cost may be of no objection, silk, as said to have been employed by Guido, who had remarked its extraordinary durability in an antient tomb, and also cloths of hair and wool might become suitable bases. To treat of the peculiar qualities of all these in their various kinds, would carry us far beyond the bounds of utility, and the limits of our subject, to which the grounding of these is more intimate.

Grounding or priming is not in all cases necessary, as, for example, when stone, slate, glass, porcelain, &c., are employed, as was the case in some paintings of undoubted extreme antiquity; but when grounds are necessary, as upon metal, wood, and canvass, to be eligible, such grounds must partake all the qualities of a good basis, in being neither soft, friable, nor perishable.

The early painters in oil, being also painters in fresco, and accustomed to plaster grounds, appear

to have prepared their panels, &c. with plaster or stucco, upon which they employed their colours, in some cases in water, in the manner of fresco or distemper, using size to fix them, and finishing with oil vehicles and varnish; and many such pictures have stood the ordinary effects of time admirably well, as appears among the works of Paul Veronese, Titian, Correggio, and others; but, upon cloth and flexible bases, such grounds are too stiff and friable; such bases require, therefore, a ground more of their own yielding and elastic nature, and better suited to assimilate with the materials of oil-painting, such as is afforded by tempering earths and metallic oxides with the most tenacious drying oils, and laying them evenly upon the cloths, first coated or primed with size.

The preparing of grounds on cloths, he, is now, however, so well performed by several of our principal colourmen, and with so much improvement, as to require little comparative attention from the artist, beyond such general knowledge of their qualities as may enable him to choose such as are best suited to his purpose. The colour of his ground is also a matter of choice, and some artists attach great importance to peculiar hues; but, as the best must depend upon varying circumstances, there can be no tint suited to every case: and we know but of one general rule on this subject, which is, that the highest light and prevailing tone of the intended work is best adapted for the ground; but

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as this sublition is the first step in every picture, it belongs, with the design, to the artist, and not to the preparer of the ground; and the first work of the brush may, with regard to the colouring, be well employed in harmonizing the colour of the ground to the key and effect of the intended picture. It may be worthy of remark, however, that nature generally colours upon a white ground, and works entirely with transparent colours, whence the purity and splendour of her colouring: and it is to the white grounds of Paul Veronese we are greatly to attribute his vividness and purity. It was, probably, according to this rule that Titian chose to paint on a red ground, when he intended to introduce much flesh in his design, or to render red principal in his picture. It is related of the same great master, who is a prime authority in all things relating to chromatic art, that, to secure the durability and cohesion of his grounds, he imbued the canvass at the back with bees'-wax, dissolved in oil, a substance well calculated to resist damp in such a situation as Venice.

To preserve the elasticity of grounds, some drying oil should be introduced into the glue or size with which they are prepared; for the same purpose bees'-wax, sugar, treacle, albumen, &c. have been added with various degrees of eligibility and success. If the ground give way in any respect, the upper surface of the picture must fail also, and this is one of the principal causes of