Several methods of preparation have been and still are adopted. In order to retain as far as possible the impression of a picture executed without repainting, some masters have first sketched in their picture with a thin wash of a single colour, very much diluted. They thus mass in the lights and shadows and lay down the main lines of their subject, after which they attempt the final painting. This system was used for a great many i8th century pictures in which the colours work in admirably with the original sketch executed in a reddish brown wash. An example is Fragonard's "Music Lesson," which has all the spontaneity of a rapid sketch.
Even before the 18th century Rubens, whose genius delighted in the overcoming of difficulties, was naturally attracted by this method. Not content with studies or simple compositions, he painted his "Kermesse" in the Louvre and his great "Adoration of the Magi" in Antwerp directly over a ground-sketch in brown. The latter work is an unparalleled tour de force from the technical point of view. But not all artists are Rubens, and a painter who does not possess his incomparable technical mastery cannot ex ecute large-scale canvases by this method. There is, moreover, a danger; however vigorously the picture is painted, the colour in which the preliminary sketch is executed gradually tends to pre vail in the general harmony. The result of this is indeed some times admirable; the "Portrait of Helene Fourment and her children" in the Louvre owes to its warm-tinted ground sketch a golden tone which is independent of the thick coat of varnish which has been applied.
Thus this attractive, but difficult and sometimes dangerous method, can only be used for limited purposes. It is more usual for painters to make use of all the materials at their disposal for sketching in their pictures; they use all the colours of their palette for the first groundwork, which matters so much to the success of the picture and still more to how it will develop in the future, and they gradually work up to the desired colour harmony. Great masters, such as Raphael, Chardin and Delacroix, have painted in this way. But they have never lost sight of the discipline which must be observed if a painting is to keep its pristine qualities. Like the sound technicians that they were, they did not forget the twofold danger which has to be avoided in the painting of a picture : overdone brushwork and muddy overlaid colour. A canvas painted without method is doomed to perish. If a sketch is painted over while it is only half dry, the paint will become muddy and dead; if solid colours, such as ochres, are applied over fragile groundwork painted with madders, or if a dark tone is put in over a light ground which is still fresh, cracking will result. What most often happens, however, is that one part of the canvas is painted over again to correct it without sufficient care; then all the dark parts become opaque black, while the lights lose their brilliance.
In order to avoid these dangers and to ensure good and solid quality in their paint, many painters work according to a system of division of labour. They use grisaille in the form of an un diluted paste for the preparation of their works, following a method first used by Italian Renaissance artists. Their pictures are sketched in with two colours, white and black or white and brown, as in a chalk and charcoal drawing. The painter can then, without any danger of working over the colour too much, work on a particular passage or modify the composition until the balance of the whole is satisfactory. The colour can then be put in on this solid foundation of grisaille; the final painting should be executed as rapidly as possible. This method has been used by Titian in his nudes and most of his portraits, El Greco and Rubens in many of their great works, Watteau in his "Gilles," Prud'hon in nearly all his pictures, and nearer to our own time Ricard and Gustave Moreau. Some painters go so far as to obtain their final harmony simply with glazes and a few touches of impasto over a monochrome ground; a typical example of this method carried to an extreme is to be found in Reynolds' "Portrait of Master Hare" in the Louvre. It will be observed that with this method the paint never becomes heavy, the colour may in some cases fade if it is put on too lightly, but no method of work does more to protect the delicate effects of a colourist or to preserve the unity of execution.