Glass and Ceramics 179
types, considering the evolution of form and decoration, a sequence in time
and local stratigraphy of sites could be established. For the Roman period, the
typology is so well defined that dating within a range of 25 years is possible.
Trade with pottery from sites with known chronology helped to characterise
undated cultures, but also to establish economic and social factors within
communities.
A first characterisation of pottery by visual means would include the struc-
ture of the fabric (fine or coarse), its colour (red or grey, different layers?) by
looking at the core of a freshly broken piece and by looking at the surface
(polished or colour coated?). A stylistic approach would note indications of
the form, e.g.of the rim, of the pedestal base and the handles. However, iden-
tical figure types can be produced in different places or at least from raw
materials imported from different sources.
Therefore, chemical analysis is the key to provenance studies, especially
for ceramics with identical or similar figure types, for pottery with an unknown
origin or when trade routes are to be investigated.
The provenance of ceramics can be determined by using major and minor
element analysis, obtained mainly by atomic absorption spectrometry (AAS)
or X-ray fluorescence (XRF). Even more common is the interpretation of
trace element patterns (concerning elements present at less than 0.1 wt%), for
which neutron activation analysis (NAA) and inductively coupled plasma
spectrometry (ICP–AES or ICP–MS) are the most commonly used analytical
techniques.
Different clay sources can be distinguished by absolute concentrations of
trace elements, or through the degree of correlation between pairs of elements
Figure 15Glaze on ceramic, a cross section; SEM: the glaze is well linked with the ceramic
support (within the dense glaze cover, a substructure, including bubbles caused
by the production process, is visible)