Lastly, to this epoch the art of mosaic owes the great perfection which it attained, in imitating painting, not only by the means of small pieces of marble selected and cemented together, but by a composition which could produce every colour, emulate every tint, represent each degree of shade, and every part, equal to the pencil itself. Baglione attributes the improvement in this art to Muziani, whom he calls the inventor of working mosaics in oil; and that which he executed for the Cappella Gregoriana, he praises as the most beautiful mosaic that has been formed since the time of the ancients. Paolo Rossetti of Cento was employed there under Muziani, and instructed Marcello Provenzale, his fellow countryman. Both left many works beautifully painted in mosaic; and the second, who lived till the time of Paul V. painted the portrait of that Pope, and some cabinet pictures. An extensive work, as has often been the case, was the cause of improving this art. The humidity of the church of S. Peter was so detrimental to oil paintings, that from the time of Urban VIII. there existed an idea of substituting mosaics in their place. The first altarpiece was executed by a scholar of Provenzale, already mentioned, Giambatista Calandra, born in Vercelli. It represents S. Michael, and is of a small size, copied from a picture of the Cav. d'Arpino. He afterwards painted other subjects in the small cupolas, and near some windows of the church, from the cartoons of Romanelli, Lanfranco, Sacchi, and Pellegrini; but thinking his talents not sufficiently rewarded, he began to work also for individuals, and painted portraits, or copied the best productions of the old masters. Among these Pascoli particularly praises a Madonna copied from a picture of Raffaello, in possession of the Queen of Sweden, and of this and other similar works he judged that from their harmony of colour and high finishing, they were deserving of close and repeated inspection. At this time great approaches were made towards the modern style of mosaic; but this art was afterwards carried to a much higher pitch by the two Cristofori, Fabio, and his son Pietro Paolo. These artists painted the S. Petronilla, copied from the great picture of Guercino, the S. Girolamo of Domenichino, and the Baptism of Christ by Maratta. For other works by him and his successors, I refer the reader to the _Descrizione_ of the pictures of Rome above cited. I will only add, that when the works were completed for S. Peter's, lest the art might decay for want of due encouragement, it was determined to decorate the church of Loreto with similar pictures, which were executed in Rome, and transferred to that church.