case of the washes laid on with the brush, pure melted wax was
employed and not a compound or emulsion, such as is generally
assumed. Berger believes in a mixture of wax, oil and resin.
It is interesting to note that the distinguished modern painter, Arnold Bocklin, executed his picture of " Sappho " in coloured pastes composed of copal resin, turpentine and wax, manipulated with a curved spatula, and that he applied heat to fuse slightly the impasto. He believed he obtained in this way a brilliancy not to be compassed with oils.
The nature of the " cestron " technique on ivory is not known. The only existing artistic designs in ivory are executed by engraved lines, and these are sometimes filled in with coloured pastes. Exquisite work in this style exists in the Hermitage at St Petersburg, and there are examples in other museums, but this can hardly be termed en caustic painting. A better idea of the laboriously executed miniature portraits of which Pliny tells us can be gained from the small medallion portraits modelled in coloured wax that were common at, the Renaissance period and are still executed to-day. In these however the smaller details are put in with the brush and pigment.
It is known from the evidence of the Erechtheum inscription that the en caustic process was employed for the painting of ornamental patterns on architectural features of marble buildings, but there is stiU considerable doubt as to the technique employed in such forms of decorative painting as the colouring of the white plaster that covered the surfaces of stonework on monumental buildings in inferior materials. Polychrome ornament on terracotta for architectural embellishment may have been fixed by the glaze as in ordinary vase painting, but Pliny says that Agrippa figulinum opus encausto pinxil in his Thermae (xxxvi. 189). The technique of the polychrome lecuthi and of the polychrome terra-cotta statuary is not certain.
The later history of wax painting after the fall of the Western Empire is of interest in connexion with the evolution of the painter's technique as a whole. Its possible relation to oil painting will be noticed later on. Here it is enough to note that the so-called Lucca MS. of the 8th century mentions the mingling of wax with colours, and the Byzantine Mount Athos Handbook, recording probably the practice of the nth century, gives a recipe for an emulsion of partly saponified wax with size as a painting medium. A recipe of the 15th century quoted by Mrs Merrifield from the MSS. of Le Begue gives a similar composition that can be thinned with water and used to temper all sorts of colours.
§ 43. Tetnpcra Painting. [Cennino's rra//a/o, in the English edition with terminal essays by Mrs Herringham (London, 1899), is the best work to consult on the subject. The Society of Painters in Tempera published in 1907 a volume of Papers on the subject. F. Lloyd's Practical Guide to Scene Painting and Painting in Distemper (London, 1879), is chiefly about the painting of theatrical scenery, and this subject is also dealt with in articles by William Telbin in the Magazine of Art (1889), pp. 92, 195.]
The binding substances used in the tempera processes may be classed as follows: (i) Size, preferably that made from boiling down cuttings of parchment. Fish-glue, gum, especially gum tragacanth and gum arabic (the Senegal gum of commerce); glycerin, honey, milk, wine, beer, &c. (2) Eggs, in the form of (i) the yolk alone, (ii) the white alone, (iii) the whole contents of the egg beaten up, (iv) the same with the addition of the milk or sap of young shoots of the fig-tree, (v) the contents of the egg with the addition of about the same quantity of vinegar [(iv) was used in the south, (v) north of the Alps]. (3) Emulsions, in which wax or oil is mingled with substances which bring about the possibility of diluting the mixture with water. Thus oil can be made to unite mechanically (not chemically) with water by the interposition either of gum or of the yolk of egg.
Of these materials it may be noted that a size or gum tempera is always soluble in water, and is moreover always of a rather thin consistency. The latter applies also to white of egg. On the other hand the yolk of an egg makes a medium of greater body, and modern artists, especially in Germany, have painted in it with a fuU impasto. The yolk of egg or the whole egg slightly
beaten up may be used to temper powdered pigments without any dilution by means of water, and the stillest body can in this way be obtained. The medieval artists seem however always to have painted with egg thinly, diluting the yolk with about an equal quantity of water. Their panels show this, and we can argue the same from the number of successive coats of paint prescribed by Cennino and other writers. The former (ch. 165) mentions seven or eight or ten coats of colours tempered with yolk alone, that must have been well thinned with water. This point will be returned to later on. The yolk of egg is really itself an emulsion as it contains about 30% of oil or fatty matter, though in its fluid state it combines readily with water. " Egg yolk, " writes Professor Church {Chemistry, p. 74), "must be regarded as essentially an oil medium. As it dries the oil hardens, " and ultimately becomes a substance not unlike leather that is quite impervious to moisture. Hence while size tempera when dry yields to water egg tempera will resist it. Sir William Richmond gave a proof of this in evidence before a committee of the House of Lords in November 1906, describing how he had exposed a piece of plaster painted with yolk of egg medium to all weathers for six months on the roof of a church and found it at the end perfectly intact. As to the milk of young fig-shoots, it is interesting to know from Principal Laurie ( Pigments and Vehicles of the Old Masters, " in Journal of the Society of Arts, Jan. 15, 1892, p. 172) that "fig-tree belongs to the same family as the india-rubber tree, and its juice contains caoutchouc." He says, " doubtless the mixture of albumen and caoutchouc would make a very tough and protective medium."
With regard to the historical use of these different media, the medieval Italians used almost exclusively the yolk of egg medium, and this is also the favourite tempera of the moderns. In fact in Italy the word " tempera, " as used by Vasari and other writers, generally means the egg medium. On the other hand size or gum was more common north of the Alps. It is in most cases very difficult to decide what temperas were in vogue in different regions and at the various epochs of the art, and the following must not be taken for more than an approximate statement of the facts. As far as it is known, the binding material in ancient Egypt was for the most part size, while Greek influence from about 600 B.C. onwards may have led to the use of wax emulsion (Punic wax). For paintings on mummy cases, and on papyrus scrolls, the medium may have been size or gum. Professor Fhnders Petrie says it was acacia gum. The wall paintings of ancient Mesopotamia as well as those of India and the farther East generally were all in tempera, and it is noteworthy that recipes and technical practices of the East and of the West seem to be curiously alike. The exact media used are doubtful. The same doubt exists with regard to the exact processes of wall and panel painting in tempera in ancient Greece and Italy, in the East, in Byzantine times, and in the early middle ages both north and south of the Alps. The materials and processes mentioned by Phny or in the various technical handbooks are on the whole clearly established, but it is very difficult to say in particular cases what was the actual technique employed. Any certainty in this matter must be based on the results not only of superficial examination but of analysis, and the very small quantities of the materials that can be placed at the disposal of the chemist make it often impossible to arrive at a satisfactory diagnosis.
A story in Pliny (xxxv. 102) shows that the Greek panel painters, when not " encaustae, " used a water tempera, but whether size or egg was its main constituent we do not know. ApeUes is said to have covered his finished panels with a thin coat of what Pliny calls " atramentum, " which may have been a white of egg varnish, for spirit varnishes were not known in antiquity (Berger i. and ii. 183), and the Greeks do not seem to have used drying oils nor varnishes made with these. Byzantine panel painting, according to the Mount Athos Handbook, was executed as a rule in an egg tempera (Berger iii. 75), and this technique was followed later on in Italy. For Greek and Etruscan (Itahan) wall-paintings of the pagan period; for late Roman wall-paintings north of the Alps, and for Romanesque and Gothic wall-paintings.
