Once the basic metallurgical processes - ferrous or nonferrous smelting, secondary processing, casting, etc. - have been identified, further questions can be asked concerning the actual process parameters such as temperature, redox condition, and consistency of operation. Process temperatures can be estimated by comparing bulk compositions with appropriate phase diagrams; this works best for relatively simple systems where the three or four major oxides add up to more than 95wt.%. For more complex systems, experimental determinations of melting temperatures are more reliable. Both approaches rely on the assumption that the entire material was liquid during the process; the presence of un-reacted components, typically residual quartz, distorts the data. Microscopic analysis is therefore necessary to assess the degree of melting; in addition, it offers insight into the cooling history through grain size and shape criteria.
Redox conditions can be determined through Moess-bauer spectrometry; however, care has to be taken to avoid contamination through later corrosion or weathering of the material. This is again best checked through microscopic analysis; the identification and relative abundance of suitable primary iron-rich phases (metallic iron with or without carbon, fayalite, wues-tite, magnetite, hematite) gives good qualitative data about the redox conditions at the time of solidification of the slag, while any corrosion products such as iron hydroxides or partially oxidised fayalite can be identified as secondary.
The consistency with which a metallurgical process is performed indicates the level of skill, while changes over time may reflect changes in ore supply or practice. Both are archaeologically important aspects, and require that larger series of analyses of well-dated material are undertaken. Comparison of metallurgical practices between sites and regions may further reveal culturally specific styles or modes, or instances of independent development or shared technologies.
World History
