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
vcrnicc 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.
A word or two may be said here about the various subsidiary processes connected with 14th and 15th century panel painting, which are of great interest as showing the conscientious, and indeed devotional spirit in which the operations were carried out. At the outset of his Traitato Cennino gives a list of the processes the panel painter has to go through, and in subsequent chapters he describes minutely each of these. The artist must " know how to grind colours, to use glue, to fasten the linen on the panel, to prime with gesso, to scrape and smooth the gesso, to make reliefs in gesso, to put on bole, to gild, to burnish, to mix temperas, to lay on grounding colours, to transfer by pouncing through pricked lines, to sharpen lines with the stylus, to indent with little patterns, to carve, to colour, to ornament the panel, and finally to varnish it." The preliminary operations, before the artificer actually begins to " colour " or paint, will take him six years to learn, and it requires with Cennino half a hundred chapters to describe them. The wooden panel is carefully compacted and linen is glued down over its face, and over this is laid, in many successive coats, a gesso ground of slaked plaster of Paris mixed with size, with which composition raised ornaments, such as the nimbi of saints, &c., can be modelled. Both these and the flat parts of the panel are scraped and smoothed till they are like ivory. The design of the picture is then drawn out on the panel, and the outlines sharpened up with the utmost precision. The gilding of the background and of the carved woodwork in which the panel is set now follows. Armenian bole, ground finely with white of egg diluted with water, is spread over the gesso and carefully burnished as a ground for water gilding with white of egg. The gold is then burnished till it apoears almost dark (in the shadow) from its own refulgence. The delicate indented patterns which are so charming on the gilded grounds of the painted panels on East Anglian screens, such as that at Southwold, are stamped with little punches, and Cennino says this is one of the most beautiful parts of the art. In the actual painting, which is on the non-gilded part of the panel, the utmost attention is paid to the ornamentation of brocaded draperies, in which gold is used as a ground and is made to show in parts, while glazes of pigment mixed with dr^'ing oil are also used. Directions for painting the flesh, which is to be done after the draperies and background, are precise. There is an under-painting in a monochrome of terra verte and white, and over this in successive coats of great thinness the flesh-tints are spread, every tint being laid in its right position on the face, the darkest flesh-tint being shaded down to the terra verte and softened off in a tender sfumato manner. Many coats are superimposed, but the green ground^ is still to remain slightly visible. At the last the lightest flesh-tint is used to obtain the reliefs and the high lights are touched in in white. The outlines are sharpened up with red mixed with black. The varnishing process should be delayed for at least a year, and the varnish, which was evidently thick, is to be spread by the fingers over the painted surfaces, care being taken not to let the varnish go over the gold ground. This should be done if possible in the sun, but Cennino says that if the varnish be boiled it will dry without being placed in the sun.
The process thus described is not what we should call, in the modern sense, painting, for the precision and conventionality of the work and the great importance given to subsidiary details are quite opposed to the spirit of the art since the l6th century. Nevertheless, the naive simplicity of the design and the exquisite delicacy of the finish have an unfailing charm. We feel, as Cennino says, that the artist has loved and delighted in his work, and regarded his patient manipulation as a religious act. A modern artist in tempera specially praises the old work for its " breadth, transparency and purity of colour, " qualities " owing to the gradual
bringing forward of the picture from a simple outline of extreme beauty." " This outline is never lost; its beautifully opposed and harmonizing lines and masses are retained to the end, even strengthened and accentuated, giving great distinctness at a distance, even when not actually visible. A perfectly modulated monochrome of light and shade fills the outline, apparent through the overlaid glory of colour, over which again is thrown a veil of atmosphere, a refulgence of light, a suggestion of palpitating space " (Mrs Herringham's Cennino, p. 218). A difficulty in the technique is the rapid drying of the medium, that prevents the fusing of the colours together in the impasto, which is possible in oil painting. Woltmann (History 0} Painting, Eng. trans, i. 406) thought that in the north honey was mixed with the white of egg or size to prevent too rapid drying, and he wrote, " this method rendered possible a liquid and softly gradated handling, and though the Italian variety of tempera allowed greater depth in the shadows, the northern gave on the whole greater brightness." In Italy, owing to the rapid drying of the egg-yolk, modelling was often secured by hatching, which is not so pleasing in its effect as the other method of superimposing thin coats of paint one over the other till the proper effect of shading is secured. One notable quality of tempera is its transparency, which is referred to by Cennino when he says that the original under-painting of terra verte is never to be wholly obliterated.
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.
Under the heading " tempera " should be noticed another style of painting with a water-medium that is executed as a rule on a large scale and in a comparatively slight fashion. Painting for the purposes of temporary decoration on canvas or wood, so much used in the Italian cities of the Renaissance period, is of this kind. Large cartoons in colour for mural pictures or tapestry, of which Raphael's cartoons are the most famous examples, are other examples; while in modern times the technique is chiefly employed in theatrical scene painting. The pigments are tempered with size or gum, and body is given to them by whitening, pipe-clay or similar substance. Work executed in this medium dries much lighter than when it is put on, and to execute it effectively, as in the case of stage scenery, requires much skill and practice. " In the study of the art of distemper painting a source of considerable embarrassment to the inexperienced eye is that the colours when wet present such a different appearance to what they do when dr>'." So writes F. Lloyds, but W. Telbin, though he recognizes this difficulty, extols the process. " A splendid material distemper! For atmosphere unequalled, and for strength as powerful as oil, in half an hour you can do with it that which in water or oil would take one or two days!" The English word "distemper" and the French " gouache " are commonly applied to this style of broad summary painting in body-colour. " Distemper" to English ears suggests house-decoration, " tempera " the work of the artist.
§ 44. Oil Painting.— [See Eastlake, Materials Jar a History of Oil Painting (London, 1847); Merimee, Dc la peinture a I'huile (Paris, 1830); Berger, Bcitrdge zur Entwicklungs-Geschickte der Maltechnik, esp. iii. 221 sqq., and iv. (Munich, 1897), &c.; Dalbon, Les Origines de la peinture a riiuile (Paris, 1904); Ludwig, tjher die Grundsatze der Oelmalerei (Leipzig, 1876); Lessing, tjber 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 ohve 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
