Chemistry Reference
In-Depth Information
To be of value for reliable differentiation, such compositional differences
should be greater between samples from different sources than between dif-
ferent samples from a single source. Most archaeological provenance studies
have so far been related to stone, ceramics, glass, and metals. Compositional
evidence on stone was used, for example, to prove that in neolithic times,
large stones from Pembroke in Wales, in the British Isles, were transported
a distance of about 200 miles to Wiltshire in England, where they were used
to build a megalithic ring at Stonehenge (Newall 1959).
Some studies on the provenance of stone have been based on determin-
ing the weight ratios between different minor or trace elements or on the rel-
ative abundance and weight ratios of the stable isotopes of such elements as
carbon and oxygen. Thus have been studied the provenance of some types
of rock (Giauque et al. 1993; Waelkens et al. 1992), marble (Craig and Craig
1972), and pottery (Perlman and Yellin 1980; Millett and Cattling 1967).
Establishing the provenance of metals presents a most difficult problem.
With the exception of the native metals, that is, gold and silver, limited
amounts of copper, and very little iron, most metals do not occur naturally
as free metals but are combined with others, mainly as metal ores from
which they have to be extracted by
metal smelting
procedures. Unlike stone,
which is used “as is,” metal ores undergo, during
metallurgical opera-
tions
, drastic chemical changes. As a consequence of these changes, there is
usually little or no compositional correlation between the minor or trace
element in mineral ores and in the metals derived from them. On occasion,
however, the relative amount of the minor or trace elements in the ore and
in the metal smelted from it bear some relationship and make it possible to
elucidate the provenance of the metal (Cherry and Knapp 1991; La Niece
1983).
1.7.
CHRONOLOGY OF ARCHAEOLOGICAL MATERIALS
Human evolution can be understood properly only if the time element is
considered; establishing the chronology of past events and of ancient objects
has been a preoccupation of historians since history was first recorded. In
archaeology, in particular, dating ancient artifacts and structures is of fun-
damental importance, and an endless search continues for methods to accu-
rately date material remains: to establish the time of occurrence as well as
the chronological succession of past events. It has been only over the period
of the last 5000 years (however, this date varies for different geographic
regions on the surface of the planet) that written chronological data
have become available. The nonliterate past of humans (
Homo sapiens
)
