Heather Lechtman

Arsenic Bronze: Dirty Copper or Chosen Alloy? A View from the Americas

AbstractThis article is dedicated to Ronald F. TylecoteArchaeologists and historians of metallurgy have attempted to explain the gradual abandonment of arsenic bronze in favor of tin bronze in the ancient Old world by making comparisons between the mechanical properties of the two bronzes. These comparisons purport to show the superiority of copper-tin alloys over alloys of copper and arsenic, despite an absence of data on the physical properties of the copper-arsenic system. The study reported here presents the results of mechanical tests carried out on experimental samples of both types of bronze over a broad range of alloy compositions. Hardness, tensile strength, and elongation determinations were made on cold worked and hot worked (forged) material. Whereas tin bronzes can be work hardened more extensively than arsenic bronzes, the far greater ductility of arsenic bronze makes it a desirable alloy for the manufacture of thin metal sheet. The widespread use of low-arsenic copper-arsenic alloys in the ...

A Metallurgical Site Survey in the Peruvian Andes

AbstractTo help document and interpret the development of pre-Columbian metallurgy prior to the Spanish invasion of the Andes, the author conducted a survey of portions of northern and southern Peru to identify and describe early metallurgical sites including mines, ore-processing areas, smelting installations. Several of the more interesting sites are discussed in detail. Coastal and highland sources of copper ores were identified, particularly along the north coast and in the altiplano bordering Lake Titicaca. Among the most provocative results of the survey is new evidence that sulfide ores of copper were being smelted long before the arrival of the Europeans, thereby indicating a level of sophistication of Andean metallurgy not previously recognized.

The Production of Copper-arsenic Alloys in the Central Andes: Highland Ores and Coastal Smelters?

AbstractThe alloy of copper and arsenic was one of the most common metallurgical products in the central Andean area during the Late Intermediate Period (A.C. 900–1476), and a large part of that production took place at smelting sites on the north coast of what is today Peru. The research of the Battan Grande-La Leche Archaeological Project has made available for the first time a rich body of data on the smelting/refining furnaces used to win copper-arsenic metal from metallic ores at Battan Grande, a key north coast center of production of the alloy. There is general agreement that mixed ores were charged into the Battan Grande furnaces, some containing minerals that contributed primarily copper to the alloy, others that contributed primarily arsenic. Whereas the types of copper ore have been identified, the types of arsenic-bearing ores and their sources remain in question.The two arsenic minerals most likely to have been used in the north coast production of copper-arsenic alloys are enargite and arsen...

La metalurgia del bronce en los Andes Sur Centrales: Tiwanaku y San Pedro de Atacama

This study is part of a larger investigation into the development of bronze metallurgy in the central and southcentral Andes during the Middle Horizon. It focuses on the kinds of bronze alloy produced and disseminated throughout the region that lies roughly between Tiwanaku and San Pedro de Atacama. Lead isotope analysis of bronze artifacts excavated at these two places and of a wide range of metallic ores sampled from deposits in Bolivia and Northern Chile indicates that the ore sources for most of the artifacts were located and exploited in the puna and high sierra of Bolivia. These results raise questions about the movement of ore, of bronze lingots, and of bronze objects within the south-central Andean interaction sphere during the Middle Horizon.

Copper‐Arsenic Bronzes from the North Coast of Peru*

HE PRODUCTION and use of copper-arsenic bronzet (often referred to T as arsenical copper) in prehistory, in both the Old and the New World, is currently the focus of study by archaeologists and historians of technology who are attempting to understand the place of that alloy in the general development of early metallurgies and, in particular, its relation to the much better known bronze, the alloy of copper and tin, that gave the bronze age its name. To appreciate the social use of these two types of bronze-not only in the form of tools, weapons, ornaments but as symbols of status, political power and wealth -a clear understanding of their properties and the dynamics of their production must be available. Consideration of the technological factors associated with the manufacture and use of these alloys is especially important because the two bronzes are often compared from the point of view of their qualities and usefulness for particular functions. Since, in both the Old World and the New, copper-tin bronze eventually displaced the copper-arsenic

A Pre-Columbian Technique for Electrochemical Replacement Plating of Gold and Silver on Copper Objects

Pre-Columbian smiths working in northern Peru gilded and silvered copper objects by electrochemical replacement techniques that deposited films of 0.5–2 μm onto copper sheet. Platings that seem to be identical have been produced in the laboratory using gold dissolved in aqueous solutions of NaCl + KNO3 + KAl(SO4)2 · 12H2O.

Andean Metallurgy in Prehistory

The past four decades of research reveal the Andean zone of South America as a heartland of metallurgy in the prehistoric world. Complex metallurgy developed in what are today Colombia (northern Andes), Ecuador and Peru (central Andes), and Bolivia and northwest Argentina (south-central Andes). This chapter follows the central and south-central Andean contributions to this prehistoric development from its inception to its political use within the Inca state. The pan-Andean nature of metallurgy through time constitutes a major focus of the chapter with respect to extractive and production technologies and to the deeply rooted cultural components of the technologies. Distinctions between the central Andean preference for working metal and the south-central tradition of casting, or the simultaneous developments of arsenic bronze in the center and tin bronze in the south, arose within a shared framework for the appropriate social arenas in which metallurgy and its products performed: as indicators of social status, of political power, as manifestations of religious, and ritual behaviors and awe.

Assessment of the As-Cu-Ni system: An example from archaeology

Abstract During the early phase of the Middle Horizon in the southern Andes (ca. AD 400–800), the majority of bronze objects at the site of Tiwanaku (Bolivia) were made of a ternary Cu-As-Ni alloy. This highly unusual bronze alloy was cast into the form of I-shaped cramps to clamp together rectangular stone building blocks in monumental constructions. The cramps are about 19cm long and about 7cm wide at the two extreme ends of the “I”. The center section of the “I” is about 1.4 cm wide and 1.4 cm thick. In one design a cramp made of Cu-6.0 As-5.85 Ni-.27 Sb (wt.%) was cast in place into two abutting, “T-shaped” channels cut into the top surfaces of adjacent blocks. The shrinkage on solidification provided a clamping force to press the faces of the blocks together at the joint. The microstructure of the cramp shows substantial porosity and consists of a two-phase, coarse-grained, highly cored casting. The primary phase (about 79%0 is fcc Cu-base solution with AsCuNi (21%) in the grain boundaries, indicating that it formed from the mixture of liquid and fcc on cooling. An assessment of the ternary was conducted following the CALPHAD method using Thermo-Calc software, an existing binary phase diagram, and thermochemical information to define the Cu-Ni rich portion of the ternary. An existing description of the Cu-Ni system was used and the As-Cu and As-Ni assessments were derived and employed to define the ternary compound AsCuNi. No ternary solution terms were employed. The Gibbs energy of formation of this compound is assessed as -26000-2T(K) J/gm-atom and the congruent melting point calculated as 1043°C. The full binary and ternary assessment is presented.

PROCESAMIENTO DE METALES DURANTE EL HORIZONTE MEDIO EN EL ALTIPLANO SURANDINO (ESCARAMAYU, PULACAYO, POTOSÍ, BOLIVIA)

En este trabajo se presentan y se analizan los resultados alcanzados en el sector metalurgico del sitio Pulac 050 (Escaramayu, Pulacayo, Bolivia). Los estudios desarrollados en el sector han puesto en evidencia un complejo de cuatro hornos metalurgicos, los cuales se encuentran espacialmente asociados con un conjunto de recintos fechados en el Horizonte Medio. Restos de varios materiales incluyendo escorias, metales y minerales fueron encontrados junto a los hornos. Los analisis de isotopo de plomo de estos materiales sugieren fuertemente que la mena fundida en el sitio fue obtenida del deposito polimetalico de plomo, plata, cobre y zinc, de Pulacayo. Tres de los hornos parecen haber sido utilizados para fundir menas metalicas; mientras que el cuarto horno se uso para refinar, quizas, el metal impuro contenido dentro de crisoles de ceramica.

Fabrication of platinum-gold alloys in pre-Hispanic South America: issues of temperature and microstructure control

Platinum and platinum-gold metallurgy was fully developed by smiths in the Esmeraldas-Tumaco Pacific coast area of present day Ecuador and Colombia long before the arrival of Europeans in South America and centuries before platinum metallurgy became practicable in the Western world. Using gold to sinter together nuggets of native placer platinum, then alternately working and annealing the resultant solid, these South American smiths produced hard, fairly homogeneous platinum-gold alloys of a range of colors for fabrication into items of adornment, and small tools, such as needles, tweezers, awls, and fishhooks. The microstructures and compositions of sintered platinum-gold objects from La Tolita, Ecuador, and of experimentally simulated platinum-gold alloy samples were analyzed using new electron probe microanalysis (EPMA) techniques and data from the platinum-gold phase diagram in an effort to determine the fabrication temperatures used by pre-Hispanic South American smiths. A comparison of EPMA results from the simulated materials with the corresponding results from the La Tolita platinum-gold objects suggests that the platinum-gold objects were never heated as high as 1100°C and probably never contained a liquid phase. As illustrated by this comparison, the qualitative and quantitative information provided by these new digital acquisition and display techniques far exceeds what conventional line scan and x-ray dot maps could provide.