This mode of coloring, which, when applied to fine art purposes, is termed tempera painting-, is undoubtedly the most ancient, and derives its name from the fact that colors are mixed or tempered with some liquid or medium to bind their separate particles to each other, and to the surface on which the paint is applied.

The Italian noun tempera admits of the widest application, and would include any medium, even oil; but. in its restricted and proper acceptation, it means a vehicle in which the yolk of egg, beaten sometimes with the white, is the chief ingredient, diluted as required with the milky juices expressed from the shouts of the fig-tree. This is the painting strictly termed a nuovo by the Italians. Vinegar probably replaced the fig-tree juice among the northern artists, from the difficulty of obtaining the latter, and in modern use vinegar is substituted. Vinegar should be used to prevent the putrefaction of the yolk of egg, but the early Italian painters preferred the egg vehicle when it had been suffered to stand until it had become decomposed, hence the phrase "a putrido."

The artist is often compelled to have recourse to very offensive media to make known his most refined revelations. On walls, and for coarser work, such as painting on linen, warm size was occasionally used, but the egg vehicle, undiluted, was generally preferred for altar-pieces on wood. For various purposes, and at different periods, however, milk, beer, wine and media composed of water, and more or less glutinous ingredients, soluble at first in water, such as gums, have also been used. Such are the media or v cles described by the chief Italian writers, as used in t!.e days of Cimabue, Giotto and Era Angelico, and by the early painters before the invention and improvement of oil painting. The finer egg tempera in dry climates has been found to attain so firm a consistence as to withstand ordinary solvents. The use of wine in diluting these glutinous vehicles was common for a long period. Buffalinaeeo, of whom so many humorous stories are told by Boccaccio and Vasari, is related to have persuaded some nuns, for whom he painted, to supply him with their choicest wine, ostensibly for the purpose of diluting the colors, but really to he imbibed by the thirsty painter himself. The northern artists were sometimes compelled to content themselves with beer.

In the works of the northern tempera painters there are, however, very marked differences observable in the impasto or body of colors. It is certain, therefore, that these painters employed media of different degrees of consistency. In the distemper of scene-painting, the medium is weak size of glue, but plaster of paris, sufficiently diluted, is worked with the colors. The carbonate of lime, or whiting, is less active as a basis for colors than the pure lime of fresco, but it is entirely destructive of transparency. When the more viscid media were employed by the tempera painters, the effect must, with their purer use of the colors, some of which were, moreover, transparent, have been very lustrous and powerful in comparison with modern scene-painters' distemper, and these qualities were heightened by the addition of a strong varnish; still, however, tempera fell far short of oil painting in richness and transparency. The carbonate of lime, or whiting, employed as a basis is. however, less active than the pure lime of fresco. The vehicles of both modes are the same, and their practice is often combined in the same work.

Water is their common vehicle, and to give adhesion to the tints and colors in distemper painting, and make them keep their place, they are variously mixed with the size of glue, prepared commonly by dissolving about 4 ounces of glue in a gallon of water. Too much of the glue disposes the painting to crack and peel from the ground, while with too little it is friable and deficient of strength. In some cases glue may be abated, or altogether dispensed with, by employing plaster of paris sufficiently diluted and worked into the colors, by which they will acquire the consistency and appearance of oil painting, without employing their limpidness or allowing the colors to separate, while they will acquire a good surface, and keep their place in the dry with the strength of fresco, and without being liable to mildew, to which animal glue is disposed, and to which milk, and other vehicles recommended in this mode, are also subject.

There can be no doubt that distempering has its manifold advantages, and that when well done it possesses a degree of clearness and brightness, especially in white, pink, blue and lilac, which is not attainable in oil colors, owing to the admixture of the various oils, and to the changes likely to occur in them subsequent to the application of the colors.

A fruitful cause of failure in distemper work is the neglect of proper precaution in preparing the surfaces to be colored, the great point at starting, assuming that the wall has been well smoothed, or if necessary scraped, in order that the surface may present no roughness or inequalities whatever. The first stage is but seldom attended to by painters, who assume that the plasterer, as a matter of course, leaves the wall properly finished, but this must not always be taken for granted. At all events even if the work has been carried as far as it is the olasterer's duty to take it, there is no reason why the next stage should not be considered to belong to the painter, who is so well aware of the conditions on which a good result to his work depends.

The process consists in this, the plasterers having left the walls, the painters take them in hand. With a bucket of water, a sponge, a rag, and a slab of wood, 6 inches broad and 7 or 8 inches long, on the back of which a handle made of leather is placed, and it must be mentioned that the wood is cut crosswise, each board being, as it were, a slice of a tree. The workman wets the wall with his sponge, and applies his wood brush, for this the instrument practically becomes, since the ends of the fibers, directed towards the wall, act like so many closely packed hairs.