Page:EB1911 - Volume 20.djvu/542

Rh we have to choose amongst the theories of size or egg tempera, wax tempera (emulsion), and the lime painting in “fresco secco” described by Theophilus. When we come to the panel painting from the 12th to the 15th century we are on surer ground. For the north we have the technical directions of Theophilus, for the south those of Cennino. Theophilus (i. ch. xxvii.) prescribes a tempera of gum from the cherry tree, and, with some pigments, white of egg. The finished panel was to be covered with an oil varnish (vernition). Cennino prescribes a tempera of the yolk of egg alone, half and half with the pigments, which have been finely ground in water and are very liquid, so that there might be in the ultimate compound about as much water as egg. A tempera of the whole egg with the milk of fig-shoots he recommends, not for panels, but for retouching fresco-work on the wall when it is dry. Tempera panels painted with egg yolk are, like the gum tempera panels of Theophilus, to be varnished with vernice liquida (oil varnish). In these media were executed all the fine tempera panels of the early Italian and early German schools of the 15th century, and these represent a limited, but within its bounds a very perfect and interesting, form of the painter’s art.

The well-known group of the “Three Graces,” from Botticelli’s large panel of the “Allegory of Spring,” at Florence, gives the quality of tempera painting very aptly (see fig. 36, Plate X.). There is a Society of Painters in Tempera in London, and some artists are enthusiastic in their admiration of the process for its purity, sincerity and permanence.

§ 44. Oil Painting.—(See Eastlake, Materials for a History of Oil Painting (London, 1847); Merimee, De la peinture à l’huile (Paris, 1830); Berger, Beiträge zur Entwicklungs-Geschichte der Maltechnik, esp. iii. 221 sqq., and iv. (Munich, 1897), &c.; Dalbon, Les Origines de la peinture a l’huile (Paris, 1904); Ludwig, Über die Grundsätze der Oelmalerei (Leipzig, 1876); Lessing, Über das Alter der Oelmalerei, 1774.)

Oil painting is an art rather of the north than of the south and east, for its development was undoubtedly furthered by the demand for moisture-resisting media in comparatively damp climates, and, moreover, the drying oils on which the technique depends were but sparingly prepared in lands where olive oil, which does not dry, was a staple product.

Certain vegetable oils dry naturally in the air by a process of oxidization, and this drying or hardening is not accompanied by any considerable shrinking, nor by any change of colour; so that oil and substances mixed with it do not alter in volume nor in appearance as a consequence of the drying process. There may be a slow subsequent alteration in the direction of darkening or becoming more yellow; but this is another matter. Among these oils the most important is linseed oil extracted from the seeds of the flax plant, poppy oil from the seeds of the opium poppy, and nut oil from the kernels of the common walnut. With these oils, generally linseed, ordinary tube colours used by painters in oil are prepared, and oil varnishes, also used by artists, are made by dissolving in them certain resins. Their natural drying qualities can be greatly aided by subjecting them to heat, and