If it be the progress of the human mind to advance from the more easy to more difficult discoveries, we may venture to suppose that the art of engraving on wood led to that of engraving on copper; and so, to a certain extent, it probably did. Vasari, however, who wrote the history of Tuscan professors, rather than of painting itself, refers its origin to works in _niello_, or inlaid modelling work, a very ancient art, much in use, more especially at Florence, during the fifteenth century; though it was quite neglected in the following, in spite of the efforts of Cellini to support it. It was applied to household furniture, silver ornaments, and sacred vessels, such as holy cups and vases, to missals and other devotional books, and to reliquaries; as well as to profane purposes, as adorning the hilts of swords, table utensils, and many kinds of female ornaments. In some kinds of ebony desks and escrutoires it was held in great request, for its little silver statues, and modelled plates, representing figures, histories, and flowers. In the cathedral of Pistoia there still remains a large silver palliotto, adorned in places with plates, on which are figured images in niello, and little scripture histories. The method was to cut with the chisel upon the silver whatever history, portrait, or flowers, was required,[91] and afterwards to fill up the hollow part of the engraving with a mixture of silver and lead, which, from its dark colour, was called, by the ancients, _nigellum_, which our countrymen curtailed into niello; a substance which, being incorporated with the silver, produced the effect of shadow, contrasted with its clearness, and gave to the entire work the appearance of a chiaroscuro in silver. There were many excellent _niellatori_, or inlayers, who cast models with this substance, such as Forzore, brother to Parri Spinelli of Arezzo, Caradosso and Arcioni of Milan;[92] and three Florentines, who rivalled each other at S. Giovanni, Matteo Dei, Antonio del Pollaiuolo, and Maso Finiguerra; specimens of whose _paci_, cut with wonderful accuracy, acquired for them the highest reputation.