Natural Science in Archaeology

8.5 Glazes 191
from throughout the island group indicate that pottery making using local raw materials
was once a widespread industry (Dye and Dickinson 1996).
One of the most thorough and inclusive case studies of the provenance of ceramic
raw materials focused on the Bronze Age of the island of Cyprus. This study originated
in efforts to reconstruct prehistoric production and exchange systems. The
resulting monograph assesses the various analytical techniques used in sourcing
Cypriot pottery and clays (Knapp and Cherry 1994). In this assessment the authors
point out that sourcing pottery raw materials has proven exceedingly difficult.
An interesting example of temper comes from a Late Archaic to Early Woodland
(4500–3000 BP) culture in the state of South Carolina. In addition to pottery
that was sand-tempered, some pottery was fiber-tempered, visible as a secondary
porosity. This fiber material was identified as Spanish moss (Tillandsia usneoides)
(Smith and Trinkley 2006). Petrographic methods can readily identify tempers and
frequently can determine their geographic/geologic source or sources. In the state
of North Dakota, the grit temper of granodioritic composition was available from
local glacial tills (Josephs 2005).
Although geographically limited in scope, the most wide-ranging and thorough
look at the archaeomineralogy of tempers is provided by Dickinson (2006) who
examined 2223 prehistoric sherds in thin section from sites across the southwest
Pacific Ocean. These tempers included calcareous as well as terrigenous sands.
Only the latter can be assigned a source from a specific island or island group.
Petrographically the temper sands fell into three groups: (1) light mineral grains
including quartz and feldspar; (2) heavy iron-magnesium minerals and opaque
iron oxides; and (3) polycrystalline lithic fragments. In 106 cases temper had been
imported; two-thirds of these involved distances of less than 200 km, and most of
the others involved distances of 200–600 km. A few cases were recorded where
temper analysis indicated imports from 1000 km or more. This volume includes 30
instructive thin-section photomicrographs in color.
8.5 Glazes
Glazes are vitreous (glassy) coatings melted on the surfaces of pottery to make them
watertight. They may also be used to impart color and decoration to the pottery
surface. All glazes by definition contain silica, and most have compositional ranges
similar to other types of glass (see Sect. 8.7 on glass). Early glazes were derived
from silica sands and glass frits (such as those found on glazed faience beads dating
from the fourth millennium BCE in Egypt). From Egypt, Anatolia, and the Persian
Gulf colored glazes were produced from the fifth millennium. These glazes all seem
to have contained some antimony.
Glazes must contain a flux agent in order to lower the melting temperature of the
silica. Without a flux agent, the melting temperature of the glaze would also melt
and deform the ceramic body to which the glaze is applied. The range of effective
firing temperatures is different for each type of flux agent. There are both “high”