of Bronzes from Machu Picchu, Peru. 537 



At first sight, these facts seem to indicate that the Inca 

 bronzes were produced by smelting mixtures of tin and copper 

 ores, since, by such a process, it would be difficult to control 

 the composition of the resulting alloy. According to Joyce 

 (6), "it seems almost certain that the presence of tin is acci- 

 dental, since it is found in greatest quantity in those implements 

 which require it least." 



I have already remarked that metallographic testing methods 

 cannot be expected to furnish any clue to the manner in which 

 tin and copper were brought into association. Without addi- 

 tional facts of more direct application, it does not appear 

 possible to prove the genesis of these bronzes. I wish, how- 

 ever, to draw attention to a few general considerations which 

 have strengthened my belief that the present objects were 

 produced by alloying the metals, tin and copper, after obtaining 

 them in comparatively pure form. 



In the first place, both tin and copper were known in elemen- 

 tary form and the former metal must have led a transitory 

 existence (as raw material for use in bronze making), since 

 no finished objects of tin have been found in Inca ruins or 

 burial places. From a metallurgical standpoint, while it is 

 true that tin and copper occur closely associated in some 

 Peruvian ores, I find it difficult to believe that these primitive 

 people could have smelted mixed ores which would almost 

 certainly contain other metals (lead, zinc, silver) and, very 

 likely arsenic and antimony, as well as sulphur, so as to pro- 

 duce the remarkably pure copper-tin alloys in question. A 

 private communication from Mr. D. C. Babbitt, of the Cerro 

 de Pasco Mining Co., contributes analyses of table concentrates 

 from Peruvian sources showing copper and tin in association 

 together with silver, gold, tungsten, zinc, antimony, arsenic, 

 sulphur and earthy material. These complex concentrates are 

 handled with reluctance by the highly equipped smelters of 

 Swansea (Wales), on account of smelting difficulties. Mr. 

 Edmond A. Guggenheim, who has taken considerable pains to 

 gather metallurgical opinions from his associates in South 

 America, calls attention in a recent letter to the frequent occur- 

 rence of tin and copper in chemical or mineralogical combina- 

 tion; but on the other hand, to the frequent occurrence of 

 lodes carrying copper ores in association with tin ores. This 

 is true of the Bolivian tin-fields in which tin predominates 

 over the copper. He also refers to the difficulty of smelting the 

 associated ores, stating that in Cornwall, even in very remote 

 times, the two classes of ores were separated before smelting. 



