Natural Science in Archaeology

9.3 Iron Oxide Compounds 207
one – the mining district of Freiberg, Germany; group two – the mining district of
Schneeberg, Germany; group three – no determination was possible from analytical
data; group four – of those with Roman glass composition, some must have used
(reused) ancient cobalt blue mosaic tesserae to color the glass.
The Chinese were among the most advanced in early pottery production. Glazes
first appeared in China during the Shang dynasty (1300–1028 BCE) (Medley 1976).
During the Zhou dynasty (1155–255 BCE), craftsmen used feldspar glazes to mimic
the appearance of jade. The Han dynasty (206 BCE–220 CE) introduced lead glazes.
During the Tang Dynasty, lead was used to enhance colorants to produce various
shades of green, amber, and yellow. The use of an oxidizing atmosphere in the kiln
produced the famous gray-green celadon glazes (Medley 1976).
The Medieval Period was a time of enormous advances in the use of glass colorants,
making possible the creation of the elaborate stained glass that was used to
adorn European cathedrals. Copper was still used for red, but it was discovered
that manganese could be used for a pale rose-red or pink. Craftsmen also learned
to use modifiers to alter the color. Manganese oxide yielded a purple-brown color,
while manganese carbonate produced violet. The addition of iron to the manganese
produced black. The firing temperature had to be controlled carefully, since glass
colors fade above 1200°C (Newton and Davison 1989).
9.3 Iron Oxide Compounds
Iron oxides are the most universally employed pigments. They occur naturally in
some form in nearly every region of the earth. Iron oxide pigments range in color
from dull yellow to reds, purples, and browns. The hue depends primarily on the
level of hydration in the mineral. Hue is also influenced by particle size, shape,
and combination with other mineral compounds. The anhydrous varieties, such as
Fe 2 O 3 , lean toward the purplish-red and maroon hues. Hydrated iron oxides, such as
Fe 2 O 3 ·nH 2 O, lean toward the warm reds and yellows. The color can be modified by
heating the pigment and driving off water (Pomies and Menu 1999). Iron oxides are
extremely stable compounds that are resistant to alkalis, acids (weak to moderate),
and to bright light.
Table 9.1 summarizes traditional names for iron oxide compounds. Ancient
references to iron oxide pigments are particularly problematic, and, as previously
stated, it is best to avoid traditional terminology except when discussing historical
texts. There has been considerable confusion in the archaeological literature regarding
terms such as “ochre”, which has often been misused by archaeologists to refer
to any type of red deposit. Furthermore, scientists have not been able to agree on
the scientific delineation of traditional epithets used to describe iron oxides. For
example, the difference between ochre and umber is a source of contention between
some scholars (see Constantinou and Govett 1972; Robertson 1976).
A complete history of the use of iron oxide pigments would fill an entire book.
Nevertheless, a brief synopsis of the historic use of iron oxides and their associated