In the foregoing list the reader will have noticed the name of Valerio Belli, of Vicenza, who engraved more particularly on rock crystal, and executed the famous casket by Clement VII., presented to Francis I. on the occasion of the marriage of that pope's niece, Catherine de' Medicis, with Henry II., son of the French king. The then prevalent fashion for rock crystal led many artists away from the path marked out by the ancients. Amongst them were Jacopo da Trezzo, who, we are assured, engraved even on diamonds, and executed incomparable portraits on precious stones; Giuliano and Tortorino of Milan, to whom we owe those elegant cups and ornamented vases, the glory of contemporary princes, and the pride of modern collections. Jacopo da Trezzo acquired such fame in this branch of the art that he was summoned to Spain, in order to execute, in crystal and precious stones, the tabernacle for the high altar in the Escurial. He took no less than seven years to complete this work, on which his name is recorded by a Latin inscription attributed to Arias Montano.

After the sumptuous work by M. H. Barbet de Jouy, the eminent curator of the marvellous collection of gems in the Galerie d'Apollon, there is no occasion here to dwell upon the monuments therein contained. Tazze, drageoirs, hanaps, nefs, and all the many precious objects required to complete the service of the table in that era of splendour and luxury, are there represented by unrivalled specimens. But more essential to our purpose is the indication of the peculiar characters by which the age of such monumerits may be recognised. The most ancient seek their beauty mainly in the form itself, relieved perhaps by a little foliage, intended rather to conceal the faults of the stone than to embellish it. Later, the style is settled; form, delicacy of outline, purity of an ornamentation inspired by the best sources, all combine to produce a harmonious general effect. The Renaissance is now at its full development, and no more complete idea can be formed of it than from the delicate cup, with balustered stem, in the cabinet of Baron Gustave de Rothschild. Here the material is faultless, the ornamentation marked by exquisite finish and sobriety. Hence were we acquainted with any more renowned artist than the illustrious names mentioned by Vasari, we should have to assign this work to him. We now come to the beginning of the sixteenth century. Rut in the tumultuous stream of this prodigious epoch how shall we fix the successive stages of development? How detect the inventions due to the individual genius of each? Forms, elegant in their very hideousness, are found jostling the simplest imitations of nature; dragons and fishes, without prototypes, are mingled with shells supported on balustered stems, and gadrooned or fluted pedestals. These various parts, blended together by enamelled gold-work mountings, exhibit a curious circumstance, which is, that pieces forming part of the same service, and capable of being recognised by their very mounting, and by the hand that executed them, formed a complete whole, rich, not only from the costly nature of the materials employed, but also from the harmonious combinations in the colours of the gems. Notwithstanding its hyaline purity, a table centre (surtout) of rock crystal, would of itself have had a monotonous appearance. It was accordingly associated with the blood-red sardonyx, with jaspers marked by bright clear spots, with the lapis-lazuli, which in its tints resembles gems, and by its slender metallic veins has a natural affinity to goldsmiths' work.

It will be readily understood that amidst such a profusion of masterpieces, fashioned with long and patient labour, it requires no little judgment to detect the types of the age, and the processes peculiar to individual artists. Yet when these monuments are brought together, a secret instinct, a glance more unerring than reason itself, enables the practised eye to detect the slow steps by which art gradually sinks from its acme to a period of relative decay. The growth of necessary reliefs, the intricacies of sculptured ornamentation, the nature and disposition of the subjects themselves, severe at first, but at last overspreading all the space left unoccupied by the engraver on the surface of the vase; then the contrast shown by contemporary engravings and settings, on the one hand, with the gem cutter and the goldsmith's art on the other; in a word, a reference to that general harmony constituting the style peculiar to all grand historic epochs - all this enables the careful observer to arrive with some certainty at the age of vases and other objects carved out of hard stones.

A more difficult task is that of distinguishing between the various national types in the works of each successive era. What, for instance, remains to the credit of France in a competition where Italy shows her name to be legion? No feeling of national pride will ever certainly induce us to exaggerate the merits of our countrymen. The French school of gem engraving was inspired by Italy, and, as already stated, it was Matteo del Nassaro, who unquestionably kindled the first sparks of the art in France Were it a question of mere gem cutting, we might doubtless go further back, since the name of Jehan Cayon occurs so early as 1497 as a diamond cutter in Lyons, while in 1529 the same occupation was still pursued in that city by Pierre Dalieres.

Nef of rock crystal, cut and engraved. Italian workmanship of the Francis I. period. (Louvre.).