580 G. H. Mathewson — Metallograpldc Description 



blunt point. In order to study the structure of the metal in 

 the head, a cut was carried from the knob at the top along 

 the principal axis of the pin well into its shank. The section 

 was then detached by a transverse cut. The location and sur- 

 face configuration of this section is shown in the diagram, 

 fig. 46. A short section was also taken out of the lower part 

 of the shank, as indicated. A fair idea of the structural 

 characteristics of the entire object should be obtainable by 

 examination of these two pieces. 



The lower part. of the object bears evidence of far more 

 effective annealing treatment than was encountered in the case 

 of the two preceding specimens. Here, the recrystallized struc- 

 ture is predominant and only a trace of the original casting 

 structure remains in the form of shadowy cores, as shown in 

 fig. 49. As pointed out in the section on Diffusional Charac- 

 teristics, the degree of homogenization and the grain size 

 correspond so that a particular combination of the two may 

 be produced by annealing for a short time at a high temperature 

 or for a longer time at a lower temperature. In this particular 

 case, the grain count of 33 and the degree of homogenization, 

 D-F might be produced, according to the diagram, fig. S 

 which applies here, by a short annealing period of minutes 

 at 700° or a period of several hours at 625°. It is unlikely 

 that the Inca metallurgists would have resorted to a period of 

 hours in which to soften the metal when a brief period at 

 higher temperature would have been equally effective. They 

 desired to soften the lower part of the object so that further 

 extension could be effected. Very likely they annealed it more 

 than once (after corresponding working stages), but in such 

 manner that the temperature attained in the upper part, near 

 the head, fell considerably short of that attained in the lower 

 part. This is beyond question, since the upper part has just 

 started to recrystallize in the locality marked by a black dot 

 in fig. 46, and structurally represented by fig. 48, while, higher 

 up, beyond the dotted region of fig. 46, no recrystallization 

 has occurred and the original casting grains are still preserved 

 in a severely deformed condition. 



All the evidence indicates that this object was annealed with 

 decreasing intensity from the point towards the head, i. e., 

 by thrusting it part way into the fire. While we cannot deduce 

 the exact temperature-range and time of anneal from the struc- 

 ture at any point, it is practically certain that the temperature 

 of the lower portion did not greatly exceed 700°, since a very 



* See section on Diffusional Characteristics. 



