A recent analysis of the composition of the bronze doors at Hildesheim, dating from 1015 A.D., gives about seventy-six parts copper, ten lead, eight tin, four zinc; and of the ‘Bernward’ pillar ascribed to about the same date, seventy copper, twenty-three tin, and five lead. These differences may surprise us, but metal casting in those days was a matter of rule of thumb, and we may recall Cellini’s account of his cramming all his household vessels of pewter into the melting pot to make the metal flow for casting his ‘Perseus.’
[181]. Vasari’s account of the making of dies for medals and of the process of striking these is clear, and agrees with the more elaborate directions contained in the seventh and following chapters of Cellini’s Trattato dell’ Oreficeria. Cellini however, unlike Vasari, was a practical medallist, and he goes more into detail. The process employed was not the direct cutting of the matrices or dies with chisels, nor, as gems are engraved, by the use of the wheel and emery (or diamond) powder, but the stamping into them of the design required by main force, by means of specially shaped hard steel punches on which different parts of the design had been worked in relief. The steel of the matrix or die had of course to be previously softened in the fire, or these punches would have made no impression on it. When finished it was again hardened by tempering. It may be noticed that the dies from which Greek coins were struck were to all appearance engraved as gems were engraved by the direct use of cutting tools or tools that, like the wheel, wore away the material with the aid of sand or emery.
The two matrices, or dies, for the obverse and reverse of the medal, being now prepared, the medal is not immediately struck. In the case of the Greek coin a bean-shaped piece, or a disk, of plain metal, usually of silver, called a ‘blank’ or ‘flan,’ was placed between the two dies and pressed into their hollows by a blow or blows of the hammer, so that all that was engraved on them in intaglio came out on the silver in relief. Vasari’s process is more elaborate. A sort of trial medal is first struck from the matrices in a soft material such as lead or wax, and this trial medal is reproduced by the ordinary process of casting in the gold or silver or bronze which is to be the material of the final medal. This cast medal has of course the general form required, but it is not sharp nor has it a fine surface. It is therefore placed between the matrices and forcibly compressed so as to acquire all the finish of detail and texture desired.
[182]. Plaster, or stucco, is sometimes regarded as an inferior material only to be used when nothing better can be obtained. It should not however be judged from the achievements of the domestic plasterer of to-day, who has to trust sometimes to the wall-paper to keep his stuff from crumbling away. Plaster as used by the ancients, and through a good part of the mediaeval and Renaissance periods up to the eighteenth century, is a fine material, susceptible of very varied and effective artistic treatment. It was made by the Greeks of so exquisite a quality that it was equivalent to an artificial marble. It could be polished, so Vitruvius tells us, till it would reflect the beholder’s face as in a mirror, and he describes how the Roman connoisseurs of his time would actually cut out plain panels of Greek stucco from old walls and frame them into the plaster work of their own rooms, just as if they were slabs of precious marble. (De Architectura, VII, iii, 10.) Vitruvius prescribes no fewer than six successive coats of plaster for a wall, each laid on before the last is dry, the last coat being of white lime and finely powdered marble.
By the Villa Farnesina at Rome some Roman, or more probably Greek, plaster decoration was discovered a few years ago that surpassed any work of the kind elsewhere known. We find there the moulded or stamped ornament Vasari describes, as well as figure compositions modelled by hand, while the plain surfaces are in themselves a delight to the artistic eye.
Among the best and best known stucco work, in figures and ornaments, of the later Italian Renaissance, may be ranked that at Fontainebleau by Primaticcio and other artists from the peninsula who were invited thither by François I, for the decoration of the ‘Galerie François I’ and the ‘Escalier du Roi.’
[183]. The composition of these two mucilages is given by Theophilus, in the Schedula, Book one, chapter 17, and also by Cennini, Trattato, chapters 110–112.
Soft cheese from cows’ milk must, according to the earlier recipe, be shredded finely into hot water and braised in a mortar to a paste. It must then be immersed in cold water till it hardens, and then rubbed till it is quite smooth on a board and afterwards mixed with quick lime to the consistency of a stiff paste. Panels cemented with this, says Theophilus, will be held so fast when they are dry that neither moisture nor heat will bring them apart. Vasari does not seem to have such faith in the mucilage, and prefers that made from boiling down shreds of parchment and other skins. The twelfth century writer knows how to make this also. See chapter eighteen of the first Book of the Schedula.
[184]. Every museum contains examples of these delicate German carvings in hard materials.
[185]. In a Note to the ‘Introduction’ to Architecture, ante, p. [128] f., an account was given of some sculptures in travertine on the façade of the church of S. Luigi dei Francesi at Rome by a ‘Maestro Gian’ who has been conjecturally identified as a certain Jean Chavier or Chavenier of Rouen who worked at Rome in the first quarter of the sixteenth century. Vasari in this place introduces an artist of the name of ‘Maestro Janni francese,’ and the question at once arises whether he is the same person as the ‘Maestro Gian’ of Rome.