Introduction

Metal objects play a significant role in most postNeolithic societies, which is reflected in the denominators for major chronological units (Copper Age, Bronze Age, Iron Age). The sequentiality of these units further reflects the stepped introduction of major metals and alloys, spanning from the earliest use of native metals (gold and copper) probably some 10 000 years ago, and continuing to this day with the development of ever more sophisticated alloys. Here, we will restrict ourselves to the metals and alloys known before c. AD 1500, primarily the metals gold, copper, lead, silver, tin, iron, and mercury, and the alloys bronze (copper-arsenic and copper-tin), brass (copper-zinc), and steel (iron-carbon). The first origin of many metals was from natural occurrences (‘native metals’), not requiring elaborate mining activities and smelting from ores. This is limited to specific geological areas and typical of the earliest use of gold, silver, copper, iron, and mercury. Supply of metals increased dramatically with the inception and spread of mining and extractive metallurgy; the geological limitation of metal production to areas rich in specific ores, however, remained. Many civilizations flourished in areas devoid of metal ores, such as the large river valley cultures; others were rich in one metal but not another. Thus, production, trade and exchange, and recycling of metals were of considerable importance from an early period onwards. Identifying and understanding these past human activities from the archaeological record requires chemical analysis in conjunction with traditional archaeological approaches.

Reason for Analysis

The use of metal objects can be seen as falling in one of three broad categories: decorative (jewelery, inlays), military (arms and armor), and domestic (tools, general implements). These exploit different metal properties perceptible in antiquity, such as color, sonority, density, malleability, hardness etc. One reason to analyze metal objects is to understand whether for a given object these properties have been either selectively exploited, or even modified to suit the purpose. This acquaints the analyzer with the state of metallurgical knowledge, or relative priorities of these parameters, and of the person or society producing the object. Reconstructing the techniques used to smelt and process metals from the waste left behind is a closely related field. Another reason is to discuss the functionality of objects, for example, whether they were made for display only or for real use; this can be a question for funerary or dedicatory objects. Chemical analysis is also a main avenue toward identifying the geological origin of a given object, in particular in combination with isotopic analysis. Basic curiosity, the desire to classify objects by material types and to identify similarities and differences in composition in order to form groups, and finally the necessity to identify the most suitable conservation methods are further reasons for analysis. Thus, four main research fields prevail in the analysis of metal objects: identifying their composition and current condition, establishing compositional groups, reconstructing metallurgical practice, and locating the geological origin of the metal. Of these four research fields, the first two are predominantly descriptive and the latter two mostly interpretative; the first and the third are absolute in that they consider only the material at hand while the second and fourth are relative as they require existing comparative material. This has major ramifications for the analytical practice; research requiring comparative data will have to match the type of existing data when conducting new analyses.