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Proceedings of Metal 2004 National Museum of Australia Canberra ACT 4–8 October 2004ABN 70 592 297 967Figure 1. Metal artifacts from the cremation pitburnt archaeological iron was Leo Biek, who noted in particular that haematite was a component of fire-scale onfreshly forged iron, and it could also be formed as a consequence of conflagrations of buildings and otherstructures (Biek 1963, 133-4; Blackwell and Biek 1985). Other citations for cremated ironwork include KingHarry Lane cemetery, Hertfordshire, where three iron nails were found to be in ‘pristine condition having beenburnt with the ‘calcined bones’ (Stead and Rigby 1989, 111). At Westhampnett Bypass, West Sussex, the firedmetalwork was noted for its fragmentary condition, discolouration and distortion or ‘molten’ appearance(Northover and Montague 1997). On the continent, the well preserved iron surgical implements from a MiddleIron Age cremation in Bavaria are described as having a ‘fine fire-patina’ (de Navarro 1955, 232).Despite this general acceptance, analysis of the deposits on archaeological artifacts does not seem to havebeen attempted. This group of iron implements provided the opportunity to characterise the surface layers andto determine how they relate to the cremation.2. Methods of analysisThe implements were initially x-rayed and also examined under a binocular microscope at low magnificationfor features of relevance to their technical descriptions. This included close examination for evidence of mineralpreserved organic materials such as handles and containers.The pin was analysed by energy-dispersive x-ray fluorescence (XRF) in an Eagle II x-ray fluorescencespectrometer with lithium-drifted silicon detector. A sample of the black deposit from the head of this pin wasremoved for x-ray diffraction (XRD) analysis, and the pin was again analysed by XRF to verify that thecomposition did not alter substantially below these layers. Surface samples from three awls and the larger knifewere also analysed by XRD.Samples in the order of 1 mg were ground in an agate mortar and mounted on a flat single-crystal siliconsample holder, designed to reduce background scatter. X-ray diffraction data were collected on a PhilipsPW1840 diffractometer using cobalt K α radiation (wavelength 0.179026 nm) incorporating a solid-state silicondetector. A search-match computer programme (Philips, based on JCPDS files) was used to identify unknowncomponents in the diffraction patterns by comparison with standards in the powder diffraction file. Jeweller’srouge powder (haematite) was also employed as a standard.The larger knife was also sampled for metallographic examination (see Figure 1), which will be reported onelsewhere, although the opportunity was taken to examine the oxidation layers by scanning electron microscopywith energy-dispersive x-ray analysis (SEM-EDS) in a Leo 4401 Stereoscan electron microscope.© Published by the National Museum of Australia www.nma.gov.au515
Proceedings of Metal 2004 National Museum of Australia Canberra ACT 4–8 October 2004ABN 70 592 297 9673. ResultsXRF analysis of the pin showed that it was made of relatively pure copper with a trace of tin (Figure 2). Thecrystalline components determined by XRD are shown in Table 1. The black deposit from the surface of the pinwas tenorite (CuO). Samples of the red deposits from the iron implements comprised haematite (Fe 2 O 3 ),sometimes with calcite (CaCO 3 ) plus trace amounts of soil components, such as quartz. Samples of the greyblacklayers on the iron comprised mainly magnetite (Fe 3 O 4 ) , with goethite (FeOOH) and lesser amounts ofhaematite and calcite.Figure 2. Non-ferrous metal pin 112. Left: XRF spectrum shows copper to be dominant. Right: XRD spectrumof the surface black layer shows mainly tenoriteTable 1. Results of XRD analysisArtifact Sample Crystalline componentsKnife 106 Red deposit from the tang calcite haematiteAwl 107 Corrosion blister from stem magnetite goethite (haematite)Awl 107 Grey-black product from stem magnetite goethite (calcite haematite)Awl 108 Red deposit from the tang calcite haematiteAwl 108 Grey-black product from stem magnetite goethite (haematite calcite)Awl 110 Red deposit from the tang tip (haematite)Pin 112 Black powder from the head tenoriteMajor constituents shown bold, minor shown normal and trace levels are bracketedAnalysis of the oxidation layers by SEM-EDS did not show any significant difference in oxygenconcentrations between the metal and the outer surface. However, the thin oxidation layer of c. 100 µmthickness did reveal a distinct compact and well-formed outer layer of c. 15 µm thickness (Figure 3). There was© Published by the National Museum of Australia www.nma.gov.au516
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Section 4: Composite artefacts (PDF 20858kb) - National Museum of ...

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