In a recent paper from Eerkens, et al. (2012) titled, "Chemical Composition, Mineralogy, and Physical Structure of Pigments on Arrow and Dart Fragments from Gypsum Cave, Nevada" the authors analyze pigments found on arrow and dart fragments to determine their chemical composition, mineralogy, and physical structure. They show that green, red, pink, brown, and black pigments were created using a variety of minerals:
The combined analyses reveal that the pigments from Gypsum Cave were produced from a variety of different minerals. None of the five subjectively-defined colors was characterized by a homogenous/standardized compositional or mineralogical recipe. This indicates that the individuals who used Gypsum Cave exploited a wide range of minerals and blended them in varying amounts to create the palate of colors seen in the weaponry fragments recovered during the archaeological investigations.
…the study demonstrated that interesting patterning existed within colors and between color and substrate type, but produced more questions than it answered. For example, analyses revealed the presence of many other non-pigmenting minerals within the paint, such as quartz, feldspar, gypsum, and various alumina-silicate minerals. It is unclear whether these were contaminants from sediments within the cave or were intentionally added to the pigments.
The authors speculate on the reasons for the different chemical compositions for the same colors on wood and can shafts. They suggest several possibilities ranging from availability during seasonal rounds and religious or traditional beliefs.
Read the paper here.
Thanks for reading and I'll see you in the field!
Eerkens, Jelmer W., Amy J Gilreath, Brian Joy
2012 Chemical Composition, Mineralogy, and Physical Structure of Pigments on Arrow and Dart Fragments from Gypsum Cave, Nevada. Journal of California and Great Basin Anthropology 32(1):47-64.