Micro‐Raman spectroscopy of carbon‐based black pigments

Abstract

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.

Raman spectroscopy for the investigation of carbon‐based black pigments

“…I Defects [43,52,54] ; soot features, [33,51,56] like mixed sp 2 -sp 3 bonds or polyenic structures [45,47,58] ; char and coal tar [48] ; diamondlike carbon in anthracite [71] ; sp 3 carbons [59,72] ; nanocrystalline diamond or trans polyene ν 1 [57] ; defects related to oxygen rich precursors as wood [60,61] From 1050 with deep UV excitation [57] to 1127 [51] to 1275 [48] [23,33,45,47,[52][53][54][55][56][57][58][59][60][61]71,72] Fullerenes Phototransformation/oxidation [38,73] 1459-1469 and 930-970 [38,73] Rhombohedral graphite B 2 2g [48] 1400 [48] ; [49] 1800 1400 1200 1000 800 1600…”

“…[8,20] The continuity of use through time and the worldwide distribution of this kind of materials require the establishment of a welldefined terminology that could be easily used for archaeometrical applications, but that keeps into account the major contributions of geological and industrial research to the study of carbon-based materials, along with the information from artistic literature (treatises [1,21,22] ). The lack of archaeometrical literature on the specific topic of distinguishing among different carbon-based black pigments [3,23] made necessary a survey of geological and industrial literature, which indeed suggested some useful ideas for data processing and interpretation, while many aspects were not considered. This latter fact is mainly because of an important consideration, which is the non-correspondence between geological and artistic nomenclature.…”

First absolute dating of Andean hunter-gatherer rock art paintings from North Central Chile

“…5), which are characteristic of the D and G bands of amorphous carbon (Tomasini et al 2012;Lahlil et al 2012). The absence of bands close to 960 cm −1 , which are characteristic of phosphates present in bony elements, leads us to dismiss the hypothesis that these elements were the raw material of the pigment (Tomasini et al 2012, Gomes et al 2013, Lahlil et al 2012.…”

Pinturas Rupestres en el Norte Semiárido de Chile: Una primera aproximación físico-química desde la Cuenca del Río Limarí (30° Lat. S)

“…Para el caso de las muestras negras, el análisis espectral identifica claramente el uso de carbón amorfo como base de la composición pictórica, lo que es evidente por la presencia de las bandas cercanas a 1335 y 1590 cm -1 , correspondiente a las bandas D y G de carbón amorfo ( fig. 6) (Lahlil et al 2012;Tomasini et al 2012b). Un análisis más acabado del perfil espectral nos permite inferir que el carbón amorfo identificado no tiene como fuente de origen restos óseos, debido a la ausencia de la banda característica cercana a 970 cm -1 (Lahlil et al 2012;Tomasini et al 2012b;Gomes et al 2013).…”

“…6) (Lahlil et al 2012;Tomasini et al 2012b). Un análisis más acabado del perfil espectral nos permite inferir que el carbón amorfo identificado no tiene como fuente de origen restos óseos, debido a la ausencia de la banda característica cercana a 970 cm -1 (Lahlil et al 2012;Tomasini et al 2012b;Gomes et al 2013). Además, en ningún caso fue posible identificar otros componentes presentes en esta capa pictórica, como por ejemplo, aglutinantes o cargas.…”