"In large altar-pieces, necessarily composed of many pieces, it may be often remarked that each separate plank has become slightly convex in front: this is particularly observable in the picture of the Transfiguration by Raphael. The heat of candles on altars is supposed to have been the cause of this not uncommon defect; but heat, if considerable, would rather produce the contrary appearance. It would seem that the layer of paint, with its substratum, slightly operates to prevent the wood from contracting or becoming concave on that side; it might therefore be concluded that a similar protection at the back, by equalizing the conditions, would tend to keep the wood flat. The oak panel on which the picture by Van Eyck in the National Gallery is painted is protected at the back by a composition of gesso, size, and tow, over which a coat of black oil-paint was passed. This, whether added when the picture was executed or subsequently, has tended to preserve the wood (which is not at all worm-eaten), and perhaps to prevent its warping."—Ib. pp. 373, 374.
On the white ground, scraped, when it was perfectly dry, till it was "as white as milk and as smooth as ivory" (Cennini), the outline of the picture was drawn, and its light and shade expressed, usually with the pen, with all possible care; and over this outline a coating of size was applied in order to render the gesso ground non-absorbent. The establishment of this fact is of the greatest importance, for the whole question of the true function and use of the gesso ground hangs upon it. That use has been supposed by all previous writers on the technical processes of painting to be, by absorbing the oil, to remove in some degree the cause of yellowness in the colors. Had this been so, the ground itself would have lost its brilliancy, and it would have followed that a dark ground, equally absorbent, would have answered the purpose as well. But the evidence adduced by Mr. Eastlake on this subject is conclusive:—
"Pictures are sometimes transferred from panel to cloth. The front being secured by smooth paper or linen, the picture is laid on its face, and the wood is gradually planed and scraped away. At last the ground appears; first, the 'gesso grosso,' then, next the painted surface, the 'gesso sottile.' On scraping this it is found that it is whitest immediately next the colors; for on the inner side it may sometimes have received slight stains from the wood, if the latter was not first sized. When a picture which happens to be much cracked has been oiled or varnished, the fluid will sometimes penetrate through the cracks into the ground, which in such parts had become accessible. In that case the white ground is stained in lines only, corresponding in their direction with the cracks of the picture. This last circumstance also proves that the ground was not sufficiently hard in itself to prevent the absorption of oil. Accordingly, it required to be rendered non-absorbent by a coating of size; and this was passed over the outline, before the oil-priming was applied."—Ib. pp. 383, 384.
The perfect whiteness of the ground being thus secured, a transparent warm oil-priming, in early practice flesh-colored, was usually passed over the entire picture. This custom, says Mr. Eastlake, appears to have been "a remnant of the old habit of covering tempera pictures with a warm varnish, and was sometimes omitted." When used it was permitted to dry thoroughly, and over it the shadows were painted in with a rich transparent brown, mixed with a somewhat thick oleo-resinous vehicle; the lighter colors were then added with a thinner vehicle, taking care not to disturb the transparency of the shadows by the unnecessary mixture of opaque pigments, and leaving the ground bearing bright through the thin lights. (?) As the art advanced, the lights were more and more loaded, and afterwards glazed, the shadows being still left in untouched transparency. This is the method of Rubens. The later Italian colorists appear to have laid opaque local color without fear even into the shadows, and to have recovered transparency by ultimate glazing.
125. Such are the principal heads of the method of the early Flemish masters, as stated by Mr. Eastlake. We have marked as questionable the influence of the ground in supporting the lights: our reasons for doing so we will give, after we have stated what we suppose to be the advantages or disadvantages of the process in its earlier stages, guiding ourselves as far as possible by the passages in which any expression occurs of Mr. Eastlake's opinion.
The reader cannot but see that the eminent character of the whole system is its predeterminateness. From first to last its success depended on the decision and clearness of each successive step. The drawing and light and shade were secured without any interference of color; but when over these the oil-priming was once laid, the design could neither be altered nor, if lost, recovered; a color laid too opaquely in the shadow destroyed the inner organization of the picture, and remained an irremediable blemish; and it was necessary, in laying color even on the lights, to follow the guidance of the drawing beneath with a caution and precision which rendered anything like freedom of handling, in the modern sense, totally impossible. Every quality which depends on rapidity, accident, or audacity was interdicted; no affectation of ease was suffered to disturb the humility of patient exertion. Let our readers consider in what temper such a work must be undertaken and carried through—a work in which error was irremediable, change impossible—which demanded the drudgery of a student, while it involved the deliberation of a master—in which the patience of a mechanic was to be united with the foresight of a magician—in which no license could be indulged either to fitfulness of temper or felicity of invention—in which haste was forbidden, yet languor fatal, and consistency of conception no less incumbent than continuity of toil. Let them reflect what kind of men must have been called up and trained by work such as this, and then compare the tones of mind which are likely to be produced by our present practice,—a practice in which alteration is admitted to any extent in any stage—in which neither foundation is laid nor end foreseen—in which all is dared and nothing resolved, everything periled, nothing provided for—in which men play the sycophant in the courts of their humors, and hunt wisps in the marshes of their wits—a practice which invokes accident, evades law, discredits application, despises system, and sets forth with chief exultation, contingent beauty, and extempore invention.
126. But it is not only the fixed nature of the successive steps which influenced the character of these early painters. A peculiar direction was given to their efforts by the close attention to drawing which, as Mr. Eastlake has especially noticed, was involved in the preparation of the design on the white ground. That design was secured with a care and finish which in many instances might seem altogether supererogatory.[18] The preparation by John Bellini in the Florentine gallery is completed with exhaustless diligence into even the portions farthest removed from the light, where the thick brown of the shadows must necessarily have afterwards concealed the greater part of the work. It was the discipline undergone in producing this preparation which fixed the character of the school. The most important part of the picture was executed not with the brush, but with the point, and the refinements attainable by this instrument dictated the treatment of their subject. Hence the transition to etching and engraving, and the intense love of minute detail, accompanied by an imaginative communication of dignity and power to the smallest forms, in Albert Dürer and others. But this attention to minutiæ was not the only result; the disposition of light and shade was also affected by the method. Shade was not to be had at small cost; its masses could not be dashed on in impetuous generalization, fields for the future recovery of light. They were measured out and wrought to their depths only by expenditure of toil and time; and, as future grounds for color, they were necessarily restricted to the natural shadow of every object, white being left for high lights of whatever hue. In consequence, the character of pervading daylight, almost inevitably produced in the preparation, was afterwards assumed as a standard in the painting. Effectism, accidental shadows, all obvious and vulgar artistical treatment, were excluded, or introduced only as the lights became more loaded, and were consequently imposed with more facility on the dark ground. Where shade was required in large mass, it was obtained by introducing an object of locally dark color. The Italian masters who followed Van Eyck's system were in the constant habit of relieving their principal figures by the darkness of some object, foliage, throne, or drapery, introduced behind the head, the open sky being left visible on each side. A green drapery is thus used with great quaintness by John Bellini in the noble picture of the Brera Gallery; a black screen, with marbled veins, behind the portraits of himself and his brother in the Louvre; a crimson velvet curtain behind the Madonna, in Francia's best picture at Bologna. Where the subject was sacred, and the painter great, this system of pervading light produced pictures of a peculiar and tranquil majesty; where the mind of the painter was irregularly or frivolously imaginative, its temptations to accumulative detail were too great to be resisted—the spectator was by the German masters overwhelmed with the copious inconsistency of a dream, or compelled to traverse the picture from corner to corner like a museum of curiosities.