576 C. H. Matheivson — Metallograipliic Description 



ber of grains counted along 31/2 " at 72 X for a half hour 

 anneal at 700° was 25. At 775° it was 16, while, in the case 

 of the Peruvian specimen, the value 23 was obtained at a 

 temperature which ran a little above 700°. 



In the region d the metal has been slightly overstrained 

 as shown by the somewhat indiscriminate occurrence of a few 

 twin crystals. This may have been caused by our own handling 

 of the piece in the vise, etc. In any event, the effects in ques- 

 tion are of little magnitude and are the result of light local 

 deformation. It is inconceivable that the hole at d, which is 

 trapezoidal in section, could have attained its present form 

 by any kind of mechanical treatment after casting. In such 

 case, no spot similar to that shown in fig. 39 at which no 

 recrystallization has occurred, could have been found at the 

 edge of the hole. (See p. 557 for description of the effect pro- 

 duced by annealing around a drilled hole.) We can only con- 

 clude that the hole was not bored, or otherwise pierced, but 

 was cast intentionally in the metal. 



In this connection, it may be well to state that this was the 

 general practise with the artisans of these objects. Other 

 cases in point will be described later. In every case examined, 

 where no other complications, i. e., indiscriminate mechanical 

 and thermal treatment after casting, have served to mask the 

 original structure, it is evident that these perforations were 

 attained in casting practise rather than by mechanical means. 

 Obviously, the perforation of so tough a metal as copper or 

 bronze in the absence of steel tools was a task incommensurate 

 with the mechanical ingenuity of these Inca craftsmen ; require- 

 ments in this direction were effectively reduced through their 

 skill in foundry practise. 



Judged from the standpoint of soundness, this specimen is 

 the best casting examined. Most of the imperfections occur 

 in the central portion of the thickest part of the metal, at b, 

 but the number of blow-holes, contraction flaws, etc., is small 

 and the piece is of good quality according to present standards. 

 The large number of holes shown in the two photo-micrographs 

 numbered 38 and 39 are in no way typical of the original metal 

 as these structures were obtained after a laboratory anneal and 

 it was thought unwise to sacrifice the specimen by removing 

 enough metal to get entirely below the partially oxidized 

 surface layer. 



