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§ 29. The Materials of Painting. — Painting begins, as we have seen, on the one side in outline delineation, on the other in the spreading of a coating of colour on a surface. For both these the material apparatus is ready at hand. Drawing may have begun merely with lines in the air, but lasting designs were soon produced either by indenting or marking any soft substance by a hard point, or by rubbing away a comparatively soft substance, such as a pointed piece of burnt wood, on a rough surface of harder grain. Almost all the materials in use for drawing are of primitive origin. Charcoal, coloured earths and soft stones are natural or easily procured. Our plumbago was known to Pliny (xxxiv. iS) and to Cennino (ch. 34), but it was not in common use till modern times. The black-lead pencil is first described as a novelty in 1565 (QueUenschriften edition of Cennino, p. 143). A metal point of ordinary lead or tin was used in medieval MSS. for drawing lines on parchment, or on a wooden surface previously whitened with chalk (Theophilus, II. ch. xvii.). Silver-point drawing is only a refinement on this. The metal point is dragged over a surface of wood or parchment that has been grounded with finely powdered bonedust, or, as in modern times, with a wash of Chinese white (Cennino, ch. 6 seq.; Church, 292), and through the actual abrasion of the metal leaves a dark line in its track. Pliny knows the technique (xxxiii. 98). When a coloured fluid was at hand a pointed stick might be used to draw lines with it, but a primitive pen would soon be made from a split reed or the wing-feather of a bird.

The coating of one substance by another of which the colour is regarded from the aesthetic standpoint is the second source of the art of painting. To manipulate the coating substance so that it will lie evenly; to spread it by suitable mechanical means; and to secure its continued adherence when duly laid, are by no means difficult. Nature provides coloured juices of vegetable or of animal origin, and it has been suggested that the blood of the slain quarry or foeman smeared by the victor over his person was the first pigment. To imitate these by mixing powdered earths or other tinted substances in water is a very simple process. Certain reeds, the fibres of which spread out in water, were used as paint-brushes in ancient Egypt. A natural hare's-foot is still employed in theatrical circles to lay on a certain kind of pigment, and no great ingenuity would be required on the part of the hunter for the manufacture of a brush from the hair or bristles of the slain beast. In the matter of securing the adhesion of the coating thus spread, nature would again be the guide. Many animal and vegetable products are sticky and ultimately dry hard, while heat or moisture thins them to convenient fluidity. Great heat makes mineral substances liquid that harden when cold. Hence binding materials offer themselves in considerable abundance, and they are of so great importance in the painter's art that they form the basis of current classifications of the different kinds of painting.

§ 30. The Surfaces covered by the Painter. — Many important questions connected with the technique of painting depend on the nature of surfaces; for the covering coat — though from the present point of view only of interest aesthetically — may, as we have seen, originally serve a utilitarian purpose. The surface in question may be classed as follows: the human body; implements, vessels, weapons, articles of dress; objects of furniture, including books; boats and ships; walls and other parts of buildings; panels and other surfaces prepared especially or entirely to be painted on.

The differences among these from the present point of view are obvious. The body could not suitably be covered with a substance impervious to air and moisture; the coatings of a clay vessel and of a boat should on the other hand make them waterproof. The materials used in building often require protection from the weather. The painting on the prepared panel needs to resist time and any special influence due to location or climate. All such considerations are prior to the questions of colour, design, or aesthetic effect generally, in these

coatings; and on them depend the binding materials, or media, with which the colouring substances are apphed. The case of one particular surface much employed for pictorial display is exceptional. This is the wall-plaster so abundantly used for clothing an unsightly, rough, or perishable building material, Uke rubble or crude brick. This function it performs perfectly when left of its natural white or greyish hue, but its plain unbroken surface has seemed to demand some relief through colouring or a pattern, and the recognition of this led to one of the most important branches of the art, mural painting. Now lime-plaster, if painted on while it is still wet, retains upon its surface after it has dried the pigments used, although these have not been mixed with any binding material. On all other surfaces the pigments are mixed with some binding material, and on the character of this the kind of painting depends. There is thus a primary distinction between the process just referred to and all others. In the former, pigments, mixed only with water, are laid on while the plaster is wet, and from this " freshness " of the ground the process is called by an Itahan term, painting " a fresco " or " on the fresh, " though in ordinary parlance the word " fresco " has come to be used as a noun, as when we speak of the " frescoes " of Giotto. Furthermore, as " fresco " is the wall-painter's process par excellence the word is unfortunately often employed inaccurately for any mural picture, though this may have been executed by quite a different process. In contradistinction to painting " a fresco " all other processes are properly described by the Italian term " a tempera, " meaning " with a mixture." The word is used as a noun in the sense of a substance mixed with another; but it is to be regarded as the imperative of the verb temper are, which both in Latin and Italian means " to divide or proportion duly, " " to qualify by mixing, " and generally " to regulate." Tempera means strictly " mix, " just as " recipe, " also employed as a substantive, is an imperative meaning " take." In ordinary parlance, however, the word tempera is confined to a certain class of binding materials to the exclusion of others, so that the more general term " media " is the best to employ in the present connexion. We go on, therefore, to consider these various media in relation to dift'erent surfaces and conditions.

§ 31. Binding Materials or Media. — The, fundamental distinction among media is their solubility or non-solubility in water, though, as will be seen presently, some possess both these qualities. The non-soluble media are (i) of mineral, (2) of vegetable origin, (i) Of the former kind are all vitreous pastes or pottery glazes, with which imperishable coloured surfaces or designs are produced on glazed tiles used in the decoration of buildings, on ceramic products, and in all processes of enamelling. Silicate of potash, employed to fix pigments on to mural surfaces of plaster in the so-called " stereo chrome " or " water-glass " processes of wall painting (see § 37), is another mineral medium, so too is paraffin wax. In the process called (unscientificaUy) " fresco secco, " in which the painting is on dry plaster, Hme is used as a binding material for the colours. Its action here is a chemical one (see § 36). (2) Non-soluble vegetable media are drying oils, resins, waxes (including paraffin wax, which is really mineral). In ancient times wax, and to some small extent also resins, were used as a protection against moisture, as in shipbuilding and some forms of wall-painting. Resins have always remained, but wax gradually went out of use in the earlier Christian centuries, and was replaced by the new medium, not used in classical times, of drying oil. In northern lands the desire to protect painted surfaces from the moisture of the air led to a more extensive use of oils and resins than in Italy; and it was in the Netherlands that in the 15th century oil media were for the first time adopted in the regular practice of painting, which they have dominated ever since.

The soluble media are of animal and vegetable origin. Egg, yolk or white, or both combined, is the chief of the former. Next in importance are size, gained by boiling down shreds of parchment, and fish glue. Egg is the chief medium in what is specially known as " tempera " painting, while for the painting