HKB
work is so highly finished and polished that it is a marvel, and gives us to know that it was a great advantage to Luca to have been a goldsmith.
But since, on reckoning up after these works how much there had come to his hand and how much time he spent in making them, he recognized that he had gained very little and that the labour had been very great, he resolved to abandon marble and bronze and to see whether he could gather better fruits from another method. Wherefore, reflecting that clay could be worked easily and with little labour, and that it was only necessary to find a method whereby works made with it might be preserved for a long time, he set about investigating to such purpose that he found a way to defend them from the injuries of time; for, after having made many experiments, he found that by covering them with a coating of glaze, made with tin, litharge, antimony, and other minerals and mixtures fused together in a special furnace, he could produce this effect very well and make works in clay almost eternal. For this method of working, as being its inventor, he gained very great praise, and all the ages to come will therefore owe him an obligation.
Having then succeeded in this as much as he could desire, he resolved that his first works should be those that are in the arch over the bronze door which he had made for the sacristy, below the organ of S. Maria del Fiore; and therein he made a Resurrection of Christ, so beautiful for that time that it was admired, when placed in position, as something truly rare. Moved by this, the said Wardens of Works desired that the arch over the door of the other sacristy, where Donatello had made the ornament of the other organ, should be filled by Luca in the same manner with similar figures and works in terra-cotta; wherefore Luca made therein a very beautiful Jesus Christ ascending into Heaven.