It was different in the Renaissance. Vasari recommends, as obviating certain miscalculations which frequently happened, that sculptors should prepare large models by which to measure the capacities of their block of marble. But these models, described as made of a mixture of plaster, size, and cloth shavings over tow and hay, could serve only for the rough proportions and attitude; nor is there ever any allusion to any process of minute measurement, such as pointing, by which detail could be transferred from the model to the stone. Most often we hear of small wax models which the sculptors enlarged directly in the stone. Vasari, while exaggerating the skill of Michelangelo in making his David out of a block mangled by another sculptor, expresses no surprise at his having chopped the marble himself; indeed, the anecdote itself affords evidence of the commonness of such a practice, since Agostino di Duccio would not have spoilt the block if he had not cut into it rashly without previous comparison with a model.[17] We hear, besides, that Jacopo della Quercia spent twelve years over one of the gates of S. Petronio, and that other sculptors carried out similar great works with the assistance of one man, or with no assistance at all,--a proceeding which would have seemed the most frightful waste except in a time and country where half of the sculptors were originally stone-masons and the other half goldsmiths, that is to say, men accustomed to every stage, coarse or subtle, of their work. The absence of replicas of Renaissance sculpture, so striking a contrast to the scores of repetitions of Greek works, proves, moreover, that the actual execution in marble was considered an intrinsic part of the sculpture of the fifteenth century, in the same way as the painting of a Venetian master. Phidias might leave the carving of his statues to skilful workmen, once he had modelled the clay, even as the painters of the merely designing and linear schools, Perugino, Ghirlandaio, or Botticelli, might employ pupils to carry out their designs on panel or wall. But in the same way as a Titian is not a Titian without a certain handling of the brush, so a Donatello is not a Donatello, or a Mino not a Mino, without a certain individual excellence in the cutting of the marble. [Footnote 17: Several Greek vases and coins show the sculptor modelling his figure; while in Renaissance designs, from that of Nanni di Banco to a mediocre allegorical engraving in an early edition of Vasari, the sculptor, or the personified art of Sculpture, is actually working with chisel and mallet.]