of Bronzes from Machu Picchu, Peru. 529 



and the specific application of the principles involved will be 

 given in individual descriptions of the several objects. 



Additional characteristics are encountered when constitu- 

 tional changes occur during thermal treatment of the metal, 

 i. e., when the alloy is made up of two or more distinct struc- 

 ture elements differing in composition and subject to influences 

 affecting their composition, distribution, or even identity. 

 These characteristics may be used, in conjunction with the 

 others already mentioned, to supply some knowledge of the 

 past history of the object. A brief discussion of constitutional 

 relationships between tin and copper will be introduced shortly, 

 along with a table of analyses pertaining to the present set 

 of bronzes. To further the immediate appreciation of pre- 

 vailing conditions, it may be observed at this point that, while 

 all of the bronzes examined are normally composed of a single 

 structure element, the alpha solution of tin in copper, certain 

 secondary constituents of a transitory nature occur in the cast 

 metal. 



Aside from the purely micrographic aspects of the work, some 

 facts of interest may be learned from first hand observation. 

 Thus, certain of the objects, notably the long cloak pins, show 

 surfaces which may be closely simulated in wood by whittling ; 

 the separate surface elements are approximately flat and long 

 enough in some cases to indicate the use of a very broad-faced 

 hammer or even a rolling face in shaping the metal. One large 

 pin has a flattened head bearing a single perforation, which, 

 from its eccentricity and decreased diameter on one face, must 

 have existed before the head was flattened. (A cylindrical hole 

 starts to close on the hammered face.) Duplex objects, in 

 which different parts are joined mechanically, by welding, or 

 by duplex casting, may sometimes be recognized by superficial 

 examination. A case of the last named variety was found in 

 the present collection. Where surface indications are not 

 adequate, examination of a properly selected section will serve 

 to settle the question. 



The archaeologist will doubtless be inclined to look through 

 these pages for some expression as to the probable age of the 

 bronzes. Unfortunately, no inferences of this sort can be 

 drawn from examinations of this character, or from any other 

 form of examination, as far as I am aware. The rate of oxida- 

 tion, or patina formation, depends upon the purity and struc- 

 tural condition of the metal, but no laws governing the process 

 have been formulated. Cast structures are more porous and 



