Carbon-based black pigments are a wide group of dark-colored materials, which are classified according to the starting material used and their method of manufacture. Raman spectroscopy is an ideal technique for the characterization of carbonaceous matter: crystalline carbon materials present well-defined peaks, which can be easily assigned; amorphous carbon materials, on the other hand, show broad bands between 1300 and 1600 cm À1 . The aim of this work was the discrimination between carbon-based pigments by micro-Raman spectroscopy. Five carbon-based pigments provided by Zecchi (lampblack, ivory black, bistre, bitumen, and graphite), two humic-earth materials [Van Dyck (Kremer) and Earth of Kassel (Zecchi)], and a commercial wood charcoal were studied. Raman spectra of all the samples showed the characteristic bands at approximately 1580 and 1350 cm À1 ; however, a clear difference in position, width, and relative intensity could be observed for most of the samples. The resulting analysis showed that micro-Raman spectroscopy allowed the discrimination of most of the reference pigments and allowed the identification of carbon-based black pigments in two South American colonial paintings dated from the early 18th century.

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Introduction: Carbon-based pigments are a group of dark-colored materials, which are classified according to the starting material used and their manufacturing process. Raman spectroscopy is an ideal technique for the identification of carbonaceous matter. Carbon-based pigments show broad bands between 1,300 and 1,600 cm −1 but they differ in position, width and relative intensity, allowing discrimination between them. The aim of the present study was the identification of carbon-based pigments in four polychrome wooden sculptures from the Jesuit Mission La Trinidad in Paraguay.Results: Analysis of the Raman spectral parameters of the polychrome samples and comparison with those of carbon-based pigment references allowed the identification of wood charcoal, lampblack, bistre and a black earth pigment. Complementary analysis by infrared spectroscopy and elemental analysis supported the assignments. Conclusions:In this study we have provided new evidence that Raman microscopy is a powerful technique for the discrimination of carbon-based pigments in works of art. This is the first time that bistre, lampblack and a black earth pigment are identified in colonial art. The chemical information obtained on the black pigments contributed to increase our knowledge on available resources and technology used in the manufacture of the polychrome sculptures at the Jesuit Mission. This information is relevant for our studies on Colonial art.