No. 33: May-Jun 1984
From Machu Picchu, Peru, comes a unique artifact: a llama-head knife made from two types of bronze. The knife blade and stem are made from low-tin bronze (not at all unusual), but the llama head is bronze with 18% bismuth. Bismuth occurs as a native metal in Peru and it is not surprising that the Incas knew of it. This is the first artifact, however, containing any appreciable proportion of bismuth in bronze. The authors of this paper believe that the use of bismuth was intentional for at least two reasons.
(1) It gave the llama head an attractive lighter tone than the rest of the knife. (2) The handle was cast directly on the stem, and the use of bismuth in the bronze would prevent the bronze from expanding too much during solidification. The handle, therefore, would be more securely attached to the stem.
The Incas thus seem to have been better metallurgists than we have supposed.
(Gordon, Robert B., and Rutledge, John W.; "Bismuth Bronze from Machu Picchu, Peru," Science, 223:585, 1984.)