That picture was accounted, mark, of old;
A king stood bare before its sovran grace,
A reverent people shouted to behold
The picture, not the king, and even the place
Containing such a miracle grew bold."
—Mrs. Barrett Browning.
As we shall have occasion, in the following pages, to speak of fresco, secco, and tempera, as distinguished from oil painting, it will be wise to try and understand clearly what these methods of work are, and in what respects they differ from, exceed, or fall short of, the modern practice.
Tempera[22] is the old name for any vehicle used in painting. The two great divisions of painting in the Middle Ages were fresco and secco; shortly put "fresco," meaning the painting on walls when the plaster was wet; "secco," the painting when it was dry. In fresco painting no vehicle was used but water; in secco painting a tempera was used composed of white and yolk of egg. Thus, in Cennino Cennini's Treatise on Painting, written in 1437,[23] he says:—"Two sorts are good, but one is better than the other. The first tempera consists in the white and yolk of an egg into which are put some cuttings from the top of a fig-tree; beat them well together, then add some of this tempera, and not in too great quantity, to each of the vases (of colour), as if you were diluting them with water. The second kind of tempera is the yolk of the egg only, and you must know that this tempera is of universal application on walls, on pictures, and in fresco, and you cannot use too much of it, but it would be wise to take a middle course."
It is to be noted that in his instructions for colouring in fresco, Cennini is very particular to state several times that no vehicle is to be used except water. All frescoes at this time were re-touched in secco, with temperas such as above described; the fresco seems to have been somewhat similar to the first painting in oil, and to have received all its more minute details from the subsequent work in secco. This was almost inevitably the case, as from the haste with which large spaces of the wall had to be covered, there could hardly be time to put in much detail, besides, many of the colours employed could not be used in fresco,[24] though all were used to finish works originally painted in fresco. Secco had an especial province of its own; all pictures, as distinguished from wall paintings, being executed in it. It must be remembered that in the time of Giotto the use of canvas was not yet introduced, and all small designs were painted upon linen cloths, stretched tightly over the surface of a smooth panel, and covered with coats of plaster carefully trimmed;[25] the next step in the preparation of the ground was to substitute parchment stretched over wood for the prepared linen.