Natural Science in Archaeology

9.3 Iron Oxide Compounds 211
Fig. 9.1 Fragments of painted wall plaster from Umm el-Jimal, Jordan, Byzantine Period
source, the Attic silver mines, was exhausted by the time he wrote his architectural
treatise. Vitruvius identified the best “red earths” as coming from Egypt and Spain
(De Architectura 7).
Medieval treatises focused less on the sources of iron oxide and more on recipes
and methods of preparation. Despite the discovery of other red mineral pigments
and dyes, the use of iron oxide pigments and colorants continued through the Medieval
Period into the Renaissance and modern times. For a discussion of 300,000
years of the use of ochre as a pigment, see Schmandt-Besserat (1980).
In some gem-quality New Zealand jades the development of the attractive flecking
is due to agglomerations of colloidally dispersed magnetite or chromite. Darker
samples were, as could be expected, higher in total iron (Wilkins et al. 2003). The
challenge for the archaeomineralogist is successful identification and characterization
of iron oxide pigment and colorants, particularly where they have survived only
in trace amounts. Evidence of iron oxide pigments on many prehistoric artifacts
has been obliterated by weathering, careless handling, or even cleaning (Faulkner
1962). It is therefore vital to handle objects sparingly and to plan decisions regarding
artifact processing and analysis before excavation and recovery.