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Keywords:

  • shards;
  • Raman microscopy;
  • band-target entropy minimization;
  • glazed;
  • unglazed;
  • pure component spectra;
  • interference patterns

Abstract

Raman mapping measurements were performed on the glazed and unglazed surfaces of shards excavated from Yuan, Ming, and Qing dynasty strata. A number of areas on each surface were chosen. Circa 21 × 21 pixels were measured for each area using both 514 and 785-nm laser as the Raman excitation. Data were collected from 100–3600 cm−1. Many sets of spectra exhibited very intense fluorescence. In spite of the intense fluorescence, the resulting sets of spectra were collated and analyzed together using the band-target entropy minimization (BTEM) algorithm. Pure component spectral estimates of many of the major components were achieved, without the use of any a priori information such as spectral libraries. These include α-silica quartz, carbon, anatase, cobalt oxides, hematite, glassy silicate, and lanthanide complexes. In addition, two further unidentified pure component spectra A and B were recovered as well as an interference pattern due to the microscopic texture of the shards (associated with small particle/thin layer domains). The carbon was primarily present in elemental form, i.e. mixture of amorphous and graphitic (unordered and ordered domains); however there is an evidence of some partial oxidation, i.e. formation of carboxylates. The interference patterns and the lanthanide complexes were only observed when using the longer wavelength red laser. The cobalt oxides and the anatase were only observed when using the green laser. In summary, the combination of Raman microscopy and BTEM has allowed the enumeration of many of the underlying spectral patterns present and hence unambiguous identification of the major individual components present in the archaeological samples. This approach would appear applicable to other classes of archaeological materials as well. Limitations and extensions of the present approach are discussed. Copyright © 2010 John Wiley & Sons, Ltd.