The chemical characteristics of particularartefacts are used to predict where the artefacts were made, provenance their source of production, as well as to source the raw materials used.
Trang 1questions 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
unprove-nanced 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
chem-ical data obtained from known and unknown
arte-facts 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
mater-ials 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
arch-aeological 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spectroscopy (no longer used), which was superseded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
spectros-copy and mass spectrosspectros-copy (favoured techniques
since the 1990s) Instrumental neutron activation
analysis has been used for trace element determin-ation, 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 spectrom-etry and proton induced gamma ray emission spec-trometry analysis have also been used, as has electron probe microanalysis Chromatographic techniques have been applied to the study of organic archaeoma-terials and these include gas chromatography and gas chromatography mass spectrometry
Postdepositional processes can also affect the geo-chemistry of artefacts, substantially altering their geochemical signature This particularly affects cer-amics Recycling, such as the addition of scrap metals
in metal production or the addition of cullet in glass production, obscures the chemical signatures restrict-ing the use of geochemistry in provenancrestrict-ing 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 ex-traction and mining, to roasting of ores, smelting, melting, refining, alloying, casting, and the use and trade of metal artefacts (Figure 4)
Stable Isotopes
The use of stable isotope analyses in artefact proven-ance 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 stud-ies 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
Figure 3 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.)
18 GEOARCHAEOLOGY