Inca Metallurgy: Gold, Silver, Tumbaga, and the Metalsmiths of Cusco

The second great craft of the Inca state, alongside textile production, was metallurgy. The Incas had inherited a tradition of metalworking that stretched back to the Chavín and Moche periods, and they refined it into a sophisticated industry of gold, silver, and the copper-gold-silver alloy called tumbaga. Gold was associated with the mascaipacha (royal headdress) and with the sweat of the sun; silver was associated with the moon (Mama Killa) and with tears. The qori kamayoq (gold workers) and qollqa kamayoq (silversmiths) were full-time specialists attached to the Sapa Inca and to the Temple of the Sun, organized into hereditary corporations and divided into provincial workshops. The most famous examples of Inca metalwork were the “gardens” of the Coricancha in Cusco, the Temple of the Sun. The detailed treatment of the Inca textile and craft tradition is given in the related article; the capture of Atahualpa and the fate of the imperial treasure is treated in the related article.

Gold and silver in the Andean world

Gold and silver were the two principal metals of the Andean world, and they were obtained from a number of sources. The principal gold-producing region of the Inca state was the Antisuyu — the eastern Andean lowlands — where alluvial gold was extracted from the rivers and streams. The principal silver-producing region was the highland province of Chinchaysuyu, particularly the mines of Porco and Potosí in present-day Bolivia. The Spanish chroniclers recorded that the Inca state obtained the bulk of its gold and silver from tribute and from the mit’a labor obligation, and that the mit’a of the mines was one of the most onerous of the state labor obligations.

The mining of gold in the Inca state was performed in three principal ways. First, placer mining — the extraction of gold from alluvial deposits by panning and sluicing — was practiced in the rivers and streams of the Antisuyu. Second, lode mining — the extraction of gold from quartz veins — was practiced in the highlands, particularly in the province of Carabaya in the eastern Andes. Third, smelting — the extraction of gold from ore by the use of lead or copper — was practiced in the workshops of the imperial administration, particularly in the major provincial centers. The chronicler Cieza de León recorded that the smelting of gold in the Inca state was performed in small clay furnaces, in which the ore was heated in the presence of a lead or copper flux; the resulting alloy was then refined by cupellation, a process by which the lead and copper are oxidized and absorbed into the cupel, leaving a button of pure gold.

The mining and smelting of silver was performed in much the same way, although the scale of the operation was substantially larger. The principal silver mines of the Inca state were the mines of Porco and Potosí, both of which were located in the highland province of Chinchaysuyu. The mines of Porco had been worked since the pre-Inca period, and the mines of Potosí were extensively developed by the Inca state in the late fifteenth century; the chronicler Cieza de León recorded that the Inca state extracted approximately 2 to 3 metric tons of silver per year from the mines of Porco and Potosí, and that the silver was sent to the state workshops at Cusco for further refinement. The detailed treatment of the Inca provincial administration and of the mit’a labor system is given in the related articles.

Tumbaga: the Inca copper-gold alloy

A distinctive feature of Inca metallurgy was the use of the copper-gold-silver alloy called tumbaga. Tumbaga, which had been known in the Andes since the Moche period, was produced by smelting copper ore with gold and silver, and it could be polished to a wide range of colors depending on the proportion of gold, silver, and copper in the mix. The Incas used tumbaga for ornamental and ritual objects — tumi knives, plaques, headdresses, chaquira (beadwork), and figurines — and the alloy was particularly prized for its resemblance to gold when polished. The modern metallurgical analysis of surviving Inca tumbaga objects, performed by Heather Lechtman of the Massachusetts Institute of Technology in the 1990s, has shown that the alloy typically contained 50 to 70 percent copper, 20 to 40 percent gold, and small amounts of silver, with the proportions varying according to the intended use of the object.

The chemical composition of tumbaga was closely related to the technique of depletion gilding, by which the surface of a tumbaga object was enriched in gold to produce a near-pure gold surface. Depletion gilding was performed by repeated cycles of hammering, annealing, and acid-etching with plant juices; the acid-etching dissolved the copper from the surface of the object, leaving a thin layer of nearly pure gold. The technique was well within the technical capacity of the Inca metalsmiths, and the chronicler Murúa recorded that the qori kamayoq of the imperial workshops were trained in the technique from an early age. The detailed treatment of the tumbaga alloy is given in the related article on Inca architecture and engineering.

The metalsmiths of the imperial workshops

The metalsmiths of the Inca state — the qori kamayoq (gold workers) and qollqa kamayoq (silversmiths) — were full-time specialists attached to the Sapa Inca and to the Temple of the Sun, organized into hereditary corporations and divided into provincial workshops. The principal workshops of the empire were located at Cusco, at Tumebamba in the north, and at the southern province of Collagua — the principal gold-producing region of the Collasuyu. The chronicler Murúa recorded that the imperial workshop at Cusco employed approximately 200 to 300 metalsmiths, and that the metalsmiths were exempt from the mit’a labor obligation in exchange for their full-time service to the state.

The training of a metalsmith was a long process. The chronicler Cobo recorded that a young metalsmith began his training at the age of 10 or 12, and that the period of training lasted some 10 to 15 years. The training was performed in the workshops of the imperial administration, and the trainee was required to learn the techniques of smelting, casting, hammering, annealing, depletion gilding, and lost-wax casting. The trainee was also required to learn the symbolic and ritual aspects of the metalsmith’s craft, including the prayers and offerings that were performed at the beginning of each working day. The detailed treatment of the training of the metalsmiths and of the mit’a labor system is given in the related articles.

The gold gardens of the Coricancha

The most famous examples of Inca metalwork were the “gardens” of the Coricancha, the Temple of the Sun in Cusco. The chroniclers describe fields of golden maize, silver llamas, and golden and silver figurines of people and animals that the Sapa Inca and his predecessors had dedicated to the sun. The most extravagant account, by the soldier-chronicler Pedro Sancho de la Hoz (1534), recorded that the gardens contained more than 200 life-sized figures of golden animals and 20 life-sized figures of golden people; the figures included llamas, jaguars, foxes, monkeys, and other animals of the Andean fauna, as well as human figures representing the Sapa Inca, the coya, and the panaca nobles.

Most of this treasure was melted down by the Spanish in 1533–1534, after the capture of Atahualpa and the subsequent sack of the Coricancha by the soldiers of Pizarro. The chronicler Pedro Pizarro recorded that the share of the imperial treasure distributed to the Spanish soldiery in 1534 amounted to approximately 5,000 marks of silver and 1,500 marks of gold, and that a substantial portion of this was melted down from the gold gardens of the Coricancha. A substantial portion of the imperial treasure also survived in the form of small ritual objects — tumi knives, chaquira beads, miniature figurines of people and animals, and small plaques of tumbaga — that were not melted down by the Spanish and that are now in the collections of the Museo del Oro in Lima, the Ethnologisches Museum in Berlin, and the British Museum in London.

The fate of Inca metallurgy after the conquest

The Spanish conquest of 1532 and the subsequent introduction of European metallurgical techniques transformed the Andean metallurgical industry. The Spanish brought with them the ingenio — a water-powered mill for the crushing and refining of silver ore — and they established a series of silver refineries in the highlands, of which the most famous was the one at Potosí in present-day Bolivia. The mine of Potosí, which had been worked on a small scale by the Inca state, was developed by the Spanish in the 1540s and 1550s into the largest silver mine in the world; at its peak in the late sixteenth century, the mine produced approximately 200 metric tons of silver per year, and the population of the city of Potosí reached some 160,000 inhabitants. The detailed treatment of the capture of Atahualpa and of the Spanish conquest of Peru is given in the related articles; the Inca textile and craft tradition is treated in the related article.

The traditional Andean metallurgical tradition did not, however, disappear. The metalsmiths of the imperial workshops were preserved in the colonial period as a hereditary caste of artisans, and they continued to produce small objects of gold, silver, and tumbaga in the tradición mestiza style. The modern Andean silverwork of Cusco and Potosí is a direct descendant of the Inca metallurgical tradition, and the techniques of depletion gilding and lost-wax casting are still practiced in the workshops of the region. The detailed treatment of the Inca textile and craft tradition and of the Inca economy without money is given in the related articles.