Natural Science in Archaeology

8.9 Fired-Brick, Tile, and Terracotta 199
brown or grey at 1200°C” (Ashurst and Ashurst 1988, pp. 48–49). It is also common
for the color of the interior and exterior of the ceramic body to vary within a single
brick unit. For example, “in a reducing atmosphere, in which the supply of oxygen
is restricted or cut off, purple or blue bricks often with black cores are produced”.
(Ashurst and Ashurst 1988) Mineralogical compounds can affect color as follows:
Lime (high percentage) with iron traces: White
Lime (low percentage) with iron traces: Grey
Chalk (low percentage) with iron traces: Cream
Iron oxide (up to 2%): Buff
Iron oxide at 900°C in a reducing atmosphere: Brown
Iron oxide at 900°C in an oxidizing atmosphere: Bright salmon
Iron oxide at 1100°C in a reducing atmosphere: Red
Iron oxide (7–10%): Blue
Iron oxide (7%–10%) + manganese oxides: Black
In addition, the presence of vegetal matter will also produce black coloration,
sealing carbon in a black core, especially when there is a sudden increase in temperature
(Ashurst and Ashurst 1988). Using this type of information, the archaeologist
may be able to infer information regarding the sources of clay materials used in the
manufacture of brick and advances in pyrotechnology. Po River alluvial deposits,
a clay and a subordinate sand, provided the raw material for bricks for Medieval
Period buildings in Ferrara, northeast Italy. Brick makers preferred high CaO clays
to promote vitrification. Analyses of brick composition showed excess sodium, so
it is likely that sodium was added as a flux. The firing temperature appeared to be
800–1000°C (Bianchini et al. 2006).
Just as with pottery and decorative ceramics, the surface color of brick may be
modified using colored glazes. Glazes may be achieved by adding “finely ground
metallic oxides to sand sprinkled on the brick before burning, for example, manganese
– brown, . . . cobalt and manganese – black, antimony – yellow, copper – green,
cobalt – blue” (Ashurst and Ashurst 1988, p. 49). In regions where fuel was scarce,
fired-brick was reserved for constructions where the unprotected material would be
exposed to more severe atmospheric conditions (Lloyd in Singer et al. 1954, p. 465).
The manufacture of terracotta architectural units is closely related to brick and
pottery manufacture. Terracotta is Italian for “baked earth”. Terracotta had its origins
in Greece in the seventh century BCE, but the golden age of terracotta was in
Italy and Germany during the Renaissance. A wide variety of common clays were
used to make terracotta. The iron content of most clays is sufficient to give terracotta
a reddish, orangish, or brownish color. Without applying a glaze, terracotta is
not waterproof. By the time of the Zhou Dynasty in China, faience beads with cores
of quartz or glass were being produced (Liu 2005). Perhaps the most famous use of
terracotta is the terracotta army buried with the Qin emperor in 210–209 BCE.
The ancient Greeks and Romans manufactured decorative wall reliefs, friezes,
roof tiles, cornices, and gutters from coarse, fired clays (Singer et al. 1954/1956).
The ancient Romans used terracotta pipes for plumbing systems and terracotta