was inevitable that as painters gave up the use of varnish, they should gradually come to use turpentine to dilute their colours, and at the same time to paint on absorbent canvas. Mat painting has the technical advantage of avoiding the difficulty of "bloom" which was mentioned above; a deliberate attempt is made to obtain harmonies by the use of colours which do not shine because they contain less oil, either on account of their having been mixed with turpentine or on account of the oil having been absorbed by the canvas. So many admirable works have been produced by this method that we cannot fail to rejoice at a new discovery in the technique of painting. It must, never theless, be asked in all impartiality how a painting from which for one reason or another varnish has been excluded will stand the effects of time. If pictures were always to be exhibited under favourable circumstances, in a dry climate, not exposed to changes of temperature, and sheltered from dust, smoke and fumes of all kinds, we could allow varnish to be an unnecessary protection. All persons who have had occasion to see a large number of paintings will, however, have met with cases, some what rare, it is true, of 18th century decorative panels which have never been varnished. As a general rule about one centi metre of the edge of the painting is concealed by a frame or beading. The painting has not turned yellow as it would have done if it had been too heavily varnished, but at the same time it has not kept its original brilliance; it is covered, as it were, with a veil of warm grey except under the frame, where it has been protected from the light and from the impurities in the air and has preserved its original freshness. The worst feature is that there is no way of cleaning pictures of this kind. The dust fixed on the paint by the moisture in the air has become incor porated with it ; but still more, the very body of the colour has been affected. Simple tones such as light greys have remained comparatively luminous, but the reds have become purplish, the yellows have turned brown, and the browns have lost their trans parency. The dirt produced by dust fixed on the picture by the moisture of the air has worked right into the grain of the canvas. Such attacks by foreign bodies would not have had so much effect on varnish, and even if owing to circumstances the varnished pic ture had suffered an accumulation of dirt, it would still be pos sible to remove the varnish and find underneath the picture as the painter conceived it.
It is most desirable to protect these mat pictures with glass, unless a coating of wax is put over them to preserve their non shiny appearance. The merits of wax for this purpose have always been known ; it is one of the best means of preserving paintings, and it isolates them from injury from without in the same way as varnish.
(See PAINTING; LANDSCAPE PAINTING; PORTRAIT PAINTING; STILL-LIFE PAINTING; MURAL PAINTING ; FLOWER PAINTING.) (J. G. G.) BIBLIOGRAPHY.-M. P. Merrifield, Original Treatises, dating from the 12th to the 28th Centuries, on the Arts of Painting in Oils, etc. (2 vols., 1849) Leonardo da Vinci, Trattato della Pittura (Paris, 1651), Eng. trans., A Treatise on Painting, J. F. Rigaud (1802), German trans., Lionardo da Vinci: dos Buck von der Malerei, H. Ludwig (Vienna, 1882) ; C. A. du Fresnoy, De Arte Graphica Liber (Paris, 1668) , French trans., R. de Pibes (1673) , Eng. trans., W. Mason, with illustrations by Sir J. Reynolds (1783) ; G. de Lairesse, Het groot schilderboek (Amsterdam, 1707), Eng. trans., J. F. Fritsch, Treatise on the Art of Painting (1738) ; Sir Joshua Reynolds, Dis courses delivered to the Students of the Royal Academy (introd. and
notes by R. Fry, 2905) ; R. E. Raspe, A Critical Essay on Oil-painting, proving that the Art of Painting in Oils was known before the Pretended Discovery of John and Hubert Van Eyck (1781) ; L. Marcucci, Saggio analitico-chimico sopra i colori minerali, etc. (Rome, 1813) ; J. N. Paillot de Montabert, Traite complet de la peinture, vol. ix. (9 vols., 1828-29) ; J. F. L. Merimee, De la peinture a l'huile (1830) ; E. Hareux, Cours complet de peinture a l'huile (2 vols., 1901) ; Ch. Dalboy, Les procedes des Primitifs, Les origines de la peinture l'huile (1904) ; E. Dinet, Les fleaux de la peinture. Observations sur les vernis, les retouches et les couleurs (1905) ; Ch. Moreau-Vauthier, La Peinture: les divers procedes (1912) , Eng. trans., The Technique of Painting (1912), and Comment on paint aujourd'hui (1923); A. Lowe and G. de Beer, Manuel de la Peinture a l'huile (Brussels, 1916) ; J. G. Goulinat, La technique des peintres (1922) ; M. Busset, La technique moderne des tableaux (1928).
(Elaeis), a genus of palms closely allied botani cally to the coconut palm (Cocos). Two species are generally recognized, both medium-sized trees native to the tropics—one of considerable range in the Old World and the other found in South America.
The African oil-palm (E. guineensis), the source of palm oil and of palm-kernel oil, is a widely-known tree of great economic value. It occurs throughout an extensive area in tropical West Africa, and is also found in Malay archipelago and in the Sunda islands. It has been introduced into the West Indies and South America, and is grown to a limited extent in southern Florida. It is a handsome tree with a stout, deeply and coarsely ringed stem, 20 ft. to 3o ft. high, bearing at its summit a somewhat irregular crown of immense feathery leaves, I o ft. to 15 ft. long. The leaves, which are pinnately divided into from 5o to 6o nar rowly lance-shaped, sharp-pointed leaflets, are alike in colour on both sides, and are borne on stout leaf-stalks with spiny-toothed margins. The exceedingly numerous flowers are crowded on a short spadix and develop into a huge ovate fruit cluster contain ing usually from 15o to 200 reddish or orange-coloured thin skinned drupes. The ripe drupes have a red or golden pulp which surrounds from one to three black hard-shelled stones or nuts with oily kernels (seeds). Upon attaining a height of several feet this species is one of the most attractive palms, and in suitably mild climates, as in southern California, young trees are grown for purely ornamental purposes.
The South American representative of the genus, E.melanococca, is a similar but much smaller tree. The leaves yield useful fibre and the fruit, like that of the Old World species, contains oil.
Palm oil, called also palm butter and palm grease, is extracted by a process of fermentation from the pulp of the oil-palm fruit. It is a fixed, butter-like, reddish-yellow fatty oil, possessing a faint violet odour, which is remarkably persistent, being conveyed to soap manufactured from it. Its chief constituents are free palmitic acid, varying from 12% in fresh oil to 55% in older oil, together with stearic acid and glycerides of palmitic and oleic acids. Its specific gravity varies from 0.920 to 0.927; its melting point is such (80.5° F to 108.5° F) that while it is usually a liquid in the Tropics, it is a semi-solid in temperate regions. Its saponification number is 202; its iodine value ranges from 65 to 72, and its Reichert number is o.5. Palm oil is soluble in alcohol, ether, carbon bisulphide and chloroform.