ever executed." This work employed his leisure hours till he attained to old age; and though painting interrupted his labours, he did not abandon it until his death, and hence, some of the historical compositions were completed by other hands, as is supposed from his cartoons. He executed the Sacrifice of Isaac, in figures as large as life; and Moses striking the Rock, with a crowd of Hebrews rushing to catch the water, and slake their thirst; besides several other subjects, which are described by Vasari; and more minutely by Landi.[295] I shall subjoin a few observations on the mechanism of the art. The first attempt of Beccafumi was to compose a picture of inlaid wood, which was long preserved in the studio of Vanni, and afterwards was in the possession of the Counts of the Delci family. He represented the Conversion of S. Paul in this piece, by employing wood of the colours only that were necessary to produce a chiaroscuro. After this model he selected white marble for the light parts of his figures, and the very purest for the catching lights; grey marble for the middle tints, black for the shadows, and for the darkest lines he sometimes employed a black stucco. He cut the pieces of these marbles, which are all indigenous, and inlaid them so nicely that the joinings are not easily discernible. This has induced some to believe that white marble is alone employed in this pavement, and that the middle tints and shadows are formed by certain very penetrating colours, capable of softening the marble and of colouring it throughout. We learn from a letter of Gallaccini, that this idea was adopted by some natives of Siena, and it appears from another of Mariette, that this great connoisseur was impressed with it, and gained over Bottari to his opinion.[296] Inspection overturns this supposition, for we may discover the seams between the different colours; and this circumstance induces the author of the Sienese Letters and the best informed persons, to disbelieve the artificial colouring of the marble. The truth is, the secret of colouring marble was not then known, but was afterwards discovered in Siena by Michelangiolo Vanni, who has transmitted the memory of his invention to posterity.[297] He erected a monument for his father, Cav. Francesco, with columns, ornaments, festoons, and figures of children; accompanied by a genealogy of the family, which were all designed on a white slab, and every part carefully and appropriately coloured, so as to resemble mosaic of different marbles. It is supposed that the colours were imparted to the marble by some mineral essences to impregnate it, because they penetrated a considerable way. He entitles himself the inventor of this art, in the monumental inscription. A secret of this nature was known to Niccolò Tornioli, of Siena, about the year 1640; and this artist is said to have painted a Veronica in that manner, the marble of which he caused to be sawed, and the same picture