Infrared spectra of mixtures of heated and unheated clay

Solving an interpretational conundrum

Bibliographic Data

ID12133266
AuthorsIsaac Ogloblin Ramírez (0000-0001-7793-6147, Department of Maritime Civilizations, School of Archaeology and Maritime Cultures University of Haifa Haifa Israel, corresponding author), Zachary C Dunseth (0000-0003-2081-0089, Joukowsky Institute for Archaeology and the Ancient World Brown University Providence Rhode Island USA), Dina Shalem (0000-0002-5561-9172, Israel Antiquities Authority Jerusalem Israel), Ruth Shahack-Gro (0000-0001-8085-9381, Department of Maritime Civilizations, School of Archaeology and Maritime Cultures University of Haifa Haifa Israel)
Year2023
Volume38
Issue6
Pages822-829
Publication date2023-08-11
Open AccessYes
TypeARTICLE
VenueGeoarchaeology (JOURNAL)
Journal identifiersISSN: 0883-6353 • E-ISSN: 1520-6548
PublisherWiley (PUBLISHER • GB)
DOI10.1002/gea.21976
OpenAlexW4385769041
LanguageEN
Citations received6
References cited15

Fourier transform infrared (FTIR) spectroscopy is frequently used for archaeological studies related to fire, allowing, among other things, researchers to distinguish between unheated and heated clay minerals. However, heat signatures are not always clear‐cut in infrared spectra of bulk sediments, as spectra occasionally appear with ambiguous absorbance bands attributed to hydroxyl (OH) in clay minerals. This paper presents an experimental study addressing this interpretational problem by considering the effect of mixtures of heated and unheated clay, a phenomenon expected in archaeological sites. After creating experimental mixtures and testing them using bulk FTIR spectroscopy, our results indicate that even a relatively small amount of unheated clay—only ca. 5%–10% mixed into a fully heated deposit—will result in ambiguous infrared spectra that are difficult to interpret. For comparison, ambiguous bulk FTIR spectra from two archaeological contexts—an ashy fill within a pit installation and a hearth—were studied with FTIR microspectroscopy, which demonstrated the presence of unheated clay within a largely heated deposit. Micromorphological observations explain the mixed nature of the investigated archaeological contexts, in this case, primarily via bioturbation. Our results thus emphasize the importance of microcontextual analysis of clay minerals. Furthermore, these results indicate that heated deposits are likely missed altogether in some archaeological contexts where only bulk FTIR analyses have been conducted

Absorbance · Analytical Chemistry (journal · Clay minerals · Fourier transform infrared spectroscopy · Infrared · Infrared spectroscopy · Mineralogy · Optics · Physics · Spectral line · Archaeology and ancient environmental studies · Building materials and conservation · Chemical Engineering · Chemistry · Cultural Heritage Materials Analysis · Environmental Chemistry · Geology · Organic Chemistry · Spectroscopy

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