Metals from K2 and Mapungubwe : a technological study of early second millennium material culture, with an emphasis on conservation

Abstract

This thesis focuses on the conservation of iron and copper objects that mostly belong to the Iron-Age sites of K2 and Mapungubwe (825-1290 AD), the two most prominent archaeological settlements in the middle Limpopo valley area of northern South Africa. For the purpose of conservation three main objectives were considered during this study which consisted of revealing the material and methods of fabrication, evaluating physical and chemical stability, and preservation. The selected objects were in four main categories, namely round wire, strip, plate and implements, and were in various states of preservation, from heavily to low corroded. This thesis consists of seven chapters that are based on these objectives. Chapter 1, introduction, provides a short introduction to the study, presents the study objectives, a brief history of the investigation of the sites, some archaeological interpretations and a discussion on the metallurgy of the objects made by the inhabitants. Chapter 2, methodology, contains analytical methods and principles which were used in gathering and management of the data. Chapters 3 and 4 present a discussion of the methods of manufacture of the selected artefacts as well as their physical stability. In these chapters the iron and copper artefacts were respectively studied by the use of non-destructive methods such as neutron tomography and microscopy. Here, a new quantitative technique in estimating the corrosion percentage by utilizing neutron tomograms and IMAGEJ software was introduced. Some of the objects with ambiguity in their fabrication, such as iron hoes or copper bangles with a central longitudinal void, were sampled destructively for metallography examination and further chemical analyses. In the case of the manufacture of native objects the outcomes confirmed the results of previous researches. Meanwhile new light was shed regarding signs of a new technique used in the production of some type of round wire on Mapungubwe Hill (strip-drawing). In the case of the round wires that were used in the manufacture of the bangles finding the definite method of manufacture was problematic. In Chapter 5 the chemical stability and the deterioration process of the artefacts were studied with consideration of both the corrosion composition as well as the effects of environmental conditions on their formation. It indicated hydroxyl (OH-) was the prominent ions in the corrosion of iron although a high amount of soluble chloride ions were detected in the burial environment in K2. In the case of copper artefacts, both chloride and hydroxyl ions were effective in corrosion and the objects were mostly subjected to severe bronze disease. This information was gathered using analytical techniques such as Raman spectroscopy, XRD and SEM-EDS. In Chapter 6 the suitable and practical conservation methods were presented. These methods consisted of both interventive and preventive conservation and were designed on the basis of the chemical and physical stability of the objects and environmental condition in the museum and in the storage facility. In chapter 7 (conclusion) a summary and the results of the study was presented which formed the final part of the thesis.