Unprocessed FTIR, Deconvolution and 4th Derivative Spectra

Figure 5. Unprocessed spectra for Button 7 from Burial 9.

In all the unprocessed spectra, there is an intense, broad peak centered at about 1038 cm-1, as well as a broad but much weaker peak at about 713 cm-1. An example of a typical unprocessed spectrum is shown in Figure 5. If we only consider the most intense peak at 1038 cm-1, literature suggests it could indicate fired clay or metaclay (Shoval 2017).

Figure 6. Deconvolved spectra data from Button 7 from Burial 9.

After deconvolution, see Figure 6, we see that the most intense peak deconvolves into two peaks around 1049 and and a shoulder at 995 cm-1. The former peak is consistent with clay or meta clay referred to earlier, while the latter peak is consistent with the presence of feldspar and/or an alumnosilicate according to literature (Barilaro et al. 2005) as well as well as according to reference spectra of different feldspars. These two bands are verified in the 4th derivative spectra and are located between 1027-1054 and 963-993 cm-1.

Figure 7. Derivative spectra data from Button 7 from Burial 9.

In almost all the deconvolution spectra obtained (Figure 7) we found additional peaks: at about 1183, 1129, 863, 787, and 721, 693 cm-1. In the 4th derivative spectra, four of these bands are verified (those are bolded). Less clear is if the other are real or artifacts. Both deconvolution and derivative spectra are subject to artifacts unless spectra are high quality. The hardness of the chipped samples make this difficult to achieve.