18 GEOARCHAEOLOGY questions The chemical characteristics of particular artefacts are used to predict where the artefacts were made, provenance their source of production, as well as to source the raw materials used This is done by comparing the geochemical signatures of unprovenanced artefacts with the geochemical signatures of locally available raw materials, or the geochemical signature of artefacts that have been produced in known localities (Figure 3) The multi-element chemical data obtained from known and unknown artefacts is usually processed by various multivariate statistical techniques These techniques show how the samples group together, thereby suggesting a close association and possible provenance Many artefacts of material culture are artificially produced, so cannot be directly compared with local raw materials sources These include metal alloys, ceramics, glass, and faience Lithics may be compared directly with rock sources The chemistry of material artefacts has also helped to deduce what they are made of, and to suggest the technological processes involved in production The geochemical techniques used in archaeological studies have included optical emission spectroscopy (no longer used), which was superseded by atomic absorption spectroscopy (commonly used in the 1970s to the 1990s), and then more recently by inductively coupled plasma atomic emission spectroscopy and mass spectroscopy (favoured techniques since the 1990s) Instrumental neutron activation analysis has been used for trace element determination, but this technique is declining in use as reactors are closed down Surprisingly, wavelength dispersive X-ray fluorescence spectrometry has not been widely used in archaeological science However, air-path energy dispersive X-ray fluorescence spectrometry has been used regularly, especially for metals, but also for other materials, as it is a non-destructive technique Proton induced X-ray emission spectrometry and proton induced gamma ray emission spectrometry analysis have also been used, as has electron probe microanalysis Chromatographic techniques have been applied to the study of organic archaeomaterials and these include gas chromatography and gas chromatography mass spectrometry Postdepositional processes can also affect the geochemistry of artefacts, substantially altering their geochemical signature This particularly affects ceramics Recycling, such as the addition of scrap metals in metal production or the addition of cullet in glass production, obscures the chemical signatures restricting the use of geochemistry in provenancing artefacts made of metals and glass Metals and Ores Metals such as gold, silver, lead, tin, copper, iron, and arsenic were used in antiquity Some were used in their raw state, such as gold and copper, and others were alloyed, such as copper and tin to produce bronze Geoarchaeologists are concerned with all aspects of metal production, from ore sources to extraction and mining, to roasting of ores, smelting, melting, refining, alloying, casting, and the use and trade of metal artefacts (Figure 4) Stable Isotopes Figure Geochemical grouping of trace element data from Korean Celadon ceramics dating to the Koryo dynasty (twelfth century AD) The bivariate plot shows the concentrations of Cr (ppm) plotted against Th (ppm) (determined by instrumental neu tron activation analysis) for ceramic pots manufactured at differ ent kiln sites in Korea and Chinese Yue ceramics for comparison The trace element data shows that the geochemical signature of the clays used in these two Korean kiln sites are distinguishable from each other and the Chinese Yue ceramics (Reproduced from Hughes M and Joyner L (2000) In: Portal J (ed.) Korea: Art & Archaeology, British Museum Press Courtesy of the Trustees of the British Museum.) The use of stable isotope analyses in artefact provenance has increased rapidly in recent years Carbon, oxygen, sulphur, strontium, and lead have all be used to provenance materials such as lithics, metals, and glass Marble provenancing was one of the first studies to use stable isotopic data to discriminate between sources in the Aegean region A large database of the isotopic signatures of d13C and d18O for marble quarries in Greece and Turkey has been built up which has been used for provenancing artefacts and for associating broken pieces of artefacts (Figure 5) Mineralogy of Archaeomaterials Many artefacts of material culture are made from geological raw materials such as rocks for building and statuary, clays for ceramics, sand for glass