The scanty knowledge we have of all these interesting technical details will not be wondered at, if we consider that we derive it from no other class of writers than from unlearned soldiers, and monks unskilled in the practical matters of this world. But still, the principal reason for this want of information is that the Mexican artist was as jealous in keeping his devices secret, as the European. They also formed guilds, into which the apprentices were sworn, and their tongues were bound by fear as well as interest. Let us quote only one instance. The Vice-King Mendoza reports to the Emperor[15] that he offered to pardon one of those workmen, if he would disclose how he was able to counterfeit the Spanish coins in so striking a way. But the native preferred to remain silent and was put to death. Here is the place for asking the question: Would not the early Mexicans, aside from their practice of casting the above metals, have employed also that of hammering? Our reply would be emphatically in the negative, if taking the expression “hammering” in its strict meaning, which is that of working with the hammer. The writers of the Conquest have left the most explicit testimony, that the natives, only after the arrival of the Spaniards became acquainted with this instrument, and with the art of using it for working high reliefs out of a metal sheet. Moreover, the native vocabulary has no word for the metal hammer as it is commonly understood. Yet the wooden mallet was known, the so-called _quauhololli_, and used by the sculptors. In the gradual education of mankind in technical knowledge, beating of metals, of course, must have preceded casting. The ancestors of the early Mexicans, at a certain epoch, stood on the same low stage of workmanship as their more distant northern brethren. But when the inventor of the mould had taught them how to multiply the objects most in demand, by the means of this easy, rapid and almost infallible operation, we must not imagine that he had done away entirely with the old practice of beating and stretching metal with a stone. The practice, in certain cases, would have been maintained: as for instance, when a diadem, a shield, or a breastplate was to be shaped, and on occasions when the object to be made required the use of a thin flat sheet of metal. Such objects are not only described by the writers, but are also represented by the native painters. A specimen of such a kind is mentioned, which on account of its extraordinary beauty, workmanship and value left a deep impression on the conquerors. It was the present which Motezuma made to Cortes at his landing, on the _Culhua_ coast, “the two gold and silver wheels;” the one, as they said, representing the Sun, the other the Moon. According to the measures they took of them, these round discs must have had a diameter of more than five feet. It is preposterous to imagine that round sheets of this size should have been the product of casting.[16]