Page:EB1911 - Volume 20.djvu/533

Rh commonly called distemper or " gouache, " of which scene painting is typical, size is used. Milk, ox-gall, casein and other substances are also employed. Of soluble vegetable media the most used are gums of various kinds. These are common " temperas " or tempera media, and, with glycerin or honey, form the usual binding material in what is called " watercolour " painting. Wine, vinegar, the milk of fig-shoots, &c., also occur in old recipes.

Attention must be drawn to the fact that substances can be prepared for use in painting that unite soluble and insoluble media, but can be diluted with water. These substances are known as " emulsions." A wax emulsion, which is also called " saponified wax, " can be made by boiling wax in a solution of potash [in the proportions 100 bleached wax, 10 potash, 250 distilled water (Berger, Bcitrage. i. 100)] till the wax is melted. When the solution has cooled it can be diluted with cold water. An admixture of oil is also possible. This, according to Berger, is what Pliny and Vitruvius (vii. 9, 3) call " Punic wax, " a material of importance in ancient painting.

An oil emulsion can be made by mixing drying oil with water through the intermediary of gum or yolk of egg. An intimate mechanical compound, not a chemical one, is thus effected, and the mixture can be diluted with water. If gum arable be used the result is a " lean " emulsion of a milky-white colour, if yolk of egg a " fat " emulsion of a yellowish tint. When these wax or oil emulsions are dry they have the waterproof character of their non-soluble constituents.

Lastly, it must be noticed that certain substances used in the graphic arts — some of which possess in themselves a certain unctuousness — can be, as it were, rubbed into a suitably roughened, and at the same time yielding, ground, to which they will adhere, though loosely, without binding material. This is the case with charcoal, chalks and pencil. The same property is imparted by a little gum or starch to soft coloured chalks, with which is executed the kind of work called " pastel." These are now also made up with an oleaginous medium and are known as " oil pastels." Pictures can be carried out in ordinary or in oil pastels, and the work should rank as a kind of painting. The coloured films, rubbed off from the sticks of soft chalk on a suitably rough and sometimes tinted paper, are artistic in their texture and capable of producing very beautiful effects of colour. Professor Church notes also that the colours laid on in this fashion seem peculiarly durable (Chemistry, p. 293).

§ 32. The Processes of Painting: Preliminary Note. — These will be discussed from the point of view of the media employed, but certain departures from strict logical arrangement will be convenient. Thus, different processes of monumental painting on walls may be brought together though distinct media are employed. Tempera and early oil practice cannot be separated.

Painting by the use of vitreous glazes fused by heat may be noticed first, as the process comes within the scope of the article, though it has generally been applied in a purely decorative spirit, so as to be a branch of the art of ornament rather than strictly speaking of painting (see § 2).

In painting processes proper fresco takes the lead. It is in its theory the simplest of all, and at the same time it has produced some of the most splendid results recorded in the annals of the art. With the fresco process may be grouped for the sake of convenience other methods of wall-painting, which share with it at any rate some of its characteristics.

One of these subsidiary methods of wall-painting is that known as the wax process or " en caustic, " used in ancient times and revived in our own. Painting in wax, not specially on walls, was an important technique among the ancient Greeks, and the consideration of it introduces some difficult archaeological questions, at which space will not allow more than a glance. The wax used in the process, softened or melted by heat or driven by fire into the painting ground — whence the name " en caustic " ox " burning in " — is really a tempera or binding material, and we are brought here to the important subject of tempera painting in general. It will have to be noticed in this connexion what were the chief binding materials used in the so-named

technique in different lands at the various stages of the art, and what conditions were imposed on the artist by the nature of his materials. Lastly, there is the all-important process in which the binding materials are oils and varnishes, a process to which attaches so much historical and artistic interest, while a form of tempera painting that has been specially developed in modern times, that known as water-colour, may claim a concluding word.

§ a. Historical Use of the Various Processes of Painting.-The extent and nature of the employment of these processes at different periods may have here a brief notice.

Tempera painting has had a far longer history and more extended use than any other. The Spaniard Pacheco, the father-in-law and teacher of Velazquez, remarks on the veneration due to tempera because it had its birthday with art itself, and was the process in which the famous ancient artists accomplished such marvels. In the matter of antiquity, painting with vitreous glazes is its only rival: glazed tiles formed, in fact, the chief polychrome decoration for the exteriors of the palaces of Mesopotamia, and were used also in Egypt; but all the wall-paintings in ancient Egypt and Babylonia and Mycenaean Greece, all the mummy cases and papyrus rolls in the first-named country are executed in tempera, and the same is true of the wall-paintings in Italian tombs. In Greece Proper paintings on terra-cotta fixed by fire were very common in the period before the Persian wars. When monumental wall-painting came to the front just after that event it was almost certainly in tempera rather than in fresco that Polygnotus and his companions executed their masterpieces. It has been doubted whether these artists painted directly on plaster or on wooden panels fixed to the wall, but the discovery in Greece of genuine mural paintings of the Mycenaean period has set these doubts at rest. In Italy tomb-paintings actually on plaster exist from the 6th century B.C. The earlier panel painters of the 5th and 4th centuries B.C. also used tempera processes, though their exact media are not recorded. About the time of Ale.xander there seems to have been felt a demand for a style of painting in which could be obtained greater depth and brilliancy of colouring, with corresponding force in relief, than was possible in the traditional tempera; and this led to painting in a wax medium with which abundance of " body " could be secured. There are many puzzling questions connected with this ancient en caustic, but the discovery in recent years of actual specimens of the work, in the form of portraits on the late Egyptian mummy cases of the first centuries a.d. have assisted the study. Meanwhile a new technique to have been in process of evolution for use on walls, for the fresco process, in a complete or modified form, was certainly in use among the Romans.

The history of the fresco process, as will presently be seen, is somewhat puzzling. Vitruvius and Pliny knew it, and it is mentioned in the Mount Athos Handbook, vihAch incorporates the technical traditions of the art of the Eastern Empire; it appears also to have been in use in the Christian catacombs, but was not practised by the wall painters who adorned the early medieval churches south and north of the Alps. The difficulties of the process, and another reason to be noticed directly, may have led to its partial disuse in the West, but we find it again coming into vogue in Italy in the 13th and 14th centuries. In the early Christian centuries its place was taken in the monumental decoration of walls by marble inlays, and especially by glass mosaic, which is in itself an important form of wall-painting and may have put painting on plaster, and with it the fresco process, into the shade; notice will however presently be taken of a theory that seeks to establish a close technical connexion between mosaic work and the fresco painting, which, on the decline in the later medieval period of mosaic, came forward again into prominence.

The tempera processes were accordingly in vogue in early medieval times for wall-paintings (except to some extent in the East), for portable panels, and on parchment for the decoration and illustration of manuscripts. Meanwhile the