During the seventeenth and eighteenth centuries the principal mosaics executed in Italy were those which decorate the Church of St. Peter’s at Rome. In these periods the Pontifical fabrique or studio for the production of the smalto and for the execution of the mosaics was in a state of activity. The fabrique had various locations in the vicinity of the church from the time of its establishment in 1528, and was finally set up in the Vatican in 1825 by Leo XIII. The most important period in the history of the Pontifical ateliers was during the early half of the eighteenth century, when it was under the direction of Pierre-Paul Cristofari, who was assisted in the production of the variously coloured material by the chemist Mattioli. The mosaics which cover the cupolas, the altars of the various chapels, the pendentines, tympani, and other spaces, have been executed by mosaicists who were not the designers of the subjects. This was the general practice in the Renaissance periods. One noteworthy exception to this rule may be noticed in the work of the artist Muziano de Brescia, who executed the mosaics of the Gregorian Chapel at St. Peter’s from his own designs, for which work he received the commission from Pope Gregory XIII. (1572-1585). Muziano was an imitator of Michelangelo, and is best known by his work in mosaic. As a rule the mosaics of St. Peter’s, like all those of the Renaissance period, are not to be compared for dignity and repose with those of the early Christian era, nor did they fulfil the true aim of monumental wall decoration, but sought rather to imitate as closely as possible the finish of oil or fresco painting. The “Transfiguration” after Raphael is not a success as a mosaic. It is believed to have been executed by Cristofari from a drawing enlarged from the original by Stefano Pozzi (1708-1768). In the great cupola the mosaic has for its subject “The Eternal Father,” surrounded by cherubims. In other compartments are angels in adoration, cherubims, Jesus, Mary, John the Baptist, Paul, the twelve Apostles and their attributes. These mosaics are from designs by the Chevalier d’Arpin (1560-1640), and rank among the best works of their kind in St. Peter’s. In the present century there has been some noted revivals of mosaic decoration in France and in England.