PIMA Spectroscopy PIMA PROJECT

33rd International Symposium on Archaeometry--Amsterdam (April 22-26, 2002)
Characterization of Archaeological Skeletal Material Using PIMA (Portable Infrared Mineral Analyzer)
Linda Klepinger (UIUC-Anthro) and Sarah Wisseman (ATAM)

The Portable Infrared Mineral Analyzer (PIMA) can reveal crystallinity and compositional variations for several minerals based on short wave infrared harmonics of bending and stretching modes of molecular bonds. The field portability of the PIMA promises an accurate, quick and cost-effective route to the sourcing of raw materials used in archaeological artifact production. This study investigates the potential usefulness of the PIMA instrument in characterizing skeletal material from archaeological and forensic contexts.

Modern human bone is characterized by strong absorption features near 1400 nm, 1900 nm, and a double peak near 1700 nm. Less prominent features consistently fall about 1500, 1750, 2020, 2150, 2250, 2300 and 2420 nm. The peaks at 1400, 1900 and 2300 nm can be identified as OH and water, water, and carbonate respectively. A gelatin spectrum shows that the other absorption features except near 1750 are largely or completely attributable to collagen. The PIMA spectra do not reliably distinguish deer bone from human bone.

In a modern human molar all collagen features except the strong double peak at 1700 nm disappear in both cementum and enamel. The 1700 nm double peak is significantly reduced in cementum and very strongly reduced in enamel, compared to bone.

Archaeological bone from a sixth century B.C. burial at Morganina, Sicily is, within the parameters of intersample variation, virtually indistinguishable from modern bone. Cremated archaeological bone from Morgantina mimics that of modern crematorium bone in the disappearance of the major collagen peaks, even when the bone is only slightly charred; most notably, the strong collagen double peak at 1700 nm completely disappears. Thus, PIMA can distinguish cremated bone from dark soil-stained bone.

Surface PIMA spectra of skeletal tissues readily discriminate bone, enamel and cementum. It can also discriminate fragments of lightly burned bone from soil stained bone when they visually appear similar. Surprisingly, the differences as attributable to collagen, not apatite peaks. More subtle discriminations may be possible using the cancellous (spongy) part of bone that produces stronger and sharper peaks, probably due to increased surface area.

Copyright 2000. University of Illinois at Urbana-Champaign.