Ruth Ann Armitage, Professor of Chemistry at Eastern Michigan University, earned a B.A. in Chemistry from Thiel College in Greenville, PA, graduating summa cum laude in 1993. While still a student, Ruth Ann participated in an archaeological field school at Slippery Rock University that confirmed her desire to combine these seemingly disparate disciplines. She completed a Ph.D. in Analytical Chemistry at Texas A&M University with Dr. Marvin Rowe in 1998 on radiocarbon dating of charcoal-pigmented rock paintings.
Archaeological Chemistry of Rock Paintings: Radiocarbon Dating and Chemical Analysis
Rock paintings, or pictographs, are unique cultural remains that are difficult to place into archaeological contexts because they are not a part of the buried stratigraphic record of a site. Direct radiocarbon dating of the paint itself would ideally be used to determine their age. The paint is typically an inorganic pigment (iron oxides and hydroxides are common) presumably mixed with an organic binder or vehicle to make the paint flow and adhere to the rock surface. Dating rock art by conventional radiocarbon techniques would have required completely destroying the paintings; the advent of accelerator mass spectrometry (AMS) for direct measurement of 14C changed that. A plasma-chemical oxidation method was developed in the 1990s to selectively remove organic carbon from small samples of paintings, yielding CO2 for radiocarbon analysis by AMS. Some paintings contain easily recognized organic material, such as charcoal, but most do not. At EMU, we are using chromatographic and mass spectrometric methods to determine the nature of the organic material present in rock paintings, and using the plasma-chemical oxidation/AMS method to date them. Results of our work on paintings from locations around the world will be presented.
Colors of the Past: Archaeological Chemistry of Natural Dyes
Color fascinates us, and has for millennia. From the vibrant mineral colors of Paleolithic rock art to the development of mauvine, chemistry and color are inseparable. Archaeological evidence indicates that humans may have used plants as much as 30,000 years ago to give color to fibers. Ancient dyers were the earliest experimental chemists, preparing natural dyes from plants, shellfish, and insects. These dye sources can often be identified by their telltale molecules. Hear about how the Armitage group at Eastern Michigan University have worked in collaboration with fiber scientists and archaeologists to identify the dye colorants in Peruvian mummy wrappings and textile fragments from an Ohio mound site using direct mass spectrometry methods.