In Ecuador, metallurgical activity was present from at least 1500 BC, with regional styles early evolving and giving rise to high levels of technical craftsmanship and to shaping particular iconographic and decorative patterns. Copper, gold and silver were mined, processed and converted into thousands of ornaments, offerings, tools and weapons extensively used both by elites and by the common people (Roberto Lleras Perez, Metallurgy in Ancient Ecuador (Ministry of Culture of Ecuador), Archaeopress Archaeology, Oxford, England, 2015).
Dotted Circle: Central Andes; Red Circle: Northern Highlands; Blue
Circle: Altiplano; where major metallurgical sites operated anciently
In contrast to the abundance in Peru, in Bolivia there is a paucity of both natural alloys and artifacts made of arsenic bronze. Rather, tin bronze and copper–arsenic–nickel alloys seem to have been the metals utilized. According to Lechtman, the earliest occurrence of this alloy in Bolivia is found on the Bolivian Altiplano before 600 AD, with tin bronze favored for ornamental rings, while copper–arsenic– nickel appears to have been preferred for needles, nails, and chisels. The tin for tin bronze appears to have been obtained from the rich “tin belt” of the Altiplano, where it primarily occurs in the mineral cassiterite (tin oxide).
No source has yet been found for the copper–arsenic–nickel alloys, with the tin-based bronze metallurgy in northern Bolivia beginning before 600 AD. This is broadly contemporaneous with the widespread use of arsenic bronze metallurgy in nearby southern Peru and northwest Argentina. Future research is needed to understand what, if any, interaction was occurring between Bolivia and southern Peru at this time of florescence of the copper industry.
The Valley of Túcume contains 26 pyramids
covering 544 acres and one of the most important archaeological sites in Peru,
located near the coastal city of Chiclayo (Lambayeque (Sicán) and Chimú
cultures
In addition, although artifacts made of bronze alloys are the most commonly found during archaeological excavation, by Inca times, gold and silver remained the most prized metals, However, artifacts composed purely of silver or gold are extremely rare, with alloys containing a mixture of copper and gold or silver, were considerably more common. Even after the Spanish invasion, such was the case and the conquistadors were surprised that in melting down their confiscated Peruvian “golden objects” were in fact composed of copper. For centuries during pre-Columbian times, Peruvian smiths developed techniques of combining copper interiors of object in sophisticated alloying techniques had golden surfaces on alloys containing small percentages of precious metals.
Experimental archaeology has been especially important here in determining how Andean cultures manipulated alloys to accentuate desired qualities. Two of the best examples of native abilities were the processes of electrochemical replacement plating and depletion gilding.
In “electrochemical replacement,” a copper alloy was given an extremely thin and even surface coating of silver or gold. To accomplish this, silver and gold were dissolved in an acidic or corrosive solution, then a copper artifact was dipped into this solution, and a chemical reaction would occur that resulted in a very thin and even “plate” or surface coating of silver or gold. In addition, the specific color of the object could be altered simply by varying the relative amount of silver or gold in the solution.
Depleted gilding on an Andean pectoral
ornament, first century AD
Ancient objects made of noble metal alloys, that is, gold with copper and/or silver, can show the phenomenon of surface enrichment. This phenomenon is regarding the composition of the surface, which has a percentage of gold higher than that of the bulk. This enrichment, called gilding, covers several techniques for applying a gold leaf or a gold powder to solid surfaces, in order to have a thin coating of this metal on objects.
In this method, a layer of nearly pure gold is placed on an object made of gold alloy by removing the other metals from its surface in this "surface enrichment" process (Eleanor Susan Blakelock, "Never Judge a Gold Object by its Surface Analysis: A Study of Surface Phenomena in a Selection of Gold Objects,” Archaeometry, vol.58, Iss.6, 2015, pp912–929). This depletion gilding process was used by pre-Columbian populations for their “tumbaga,” a gold-copper alloy, to give it the luster of gold (Amelia Carolina Sparavigna, “Depletion Gilding: An Ancient Method for Surface Enrichment of Gold Alloys,” Mechanics, Materials Science & Engineering, Department of Applied Science and Technology, Polytechnic University of Turin, Italy, January 2016).
These are just two of the techniques in which native South Americans manipulated the appearance of metal artifacts in order to achieve a surface of silver or gold. These technologies appear to have been developed by the Moche in the first century AD on the north coast of Peru and remained a northern phenomenon until the rise of the Inca Empire in the mid-fifteenth century.
In short, a wide variety of metallurgical techniques were used by Andean cultures, and considerable skill was demonstrated in the manipulation of nonferrous ores from the last few centuries BC into the first several centuries AD. By integrating the fields of archaeology, ethno-history, and geology a great deal can still be learned about these cultures’ use of metals.
(See the next post, “Metallurgy in the Americas – Part VI,” regarding the fact that almost all metallurgists claim that metallurgy developed and began in South America and from there traveled northward into Central, Meso-, and North America)
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