Multivariate treatment of LIBS data of prehistoric paintings

• Published in: Journal of the Brazilian Chemical Society Vol. 23; no. 5; pp. 958 - 965
• Main Authors: Borba, Flávia de S. L., Cortez, Juliana, Asfora, Viviane K., Pasquini, Celio, Pimentel, Maria Fernanda, Pessis, Anne-Marie, Khoury, Helen J.
• Format: Journal Article
• Language: English
• Published: Sociedade Brasileira de Química 01-05-2012
• Subjects: CHEMISTRY, MULTIDISCIPLINARY; prehistoric paintings; laser-induced breakdown spectroscopy; LIBS; principal component analysis; depth profile
• ISSN: 0103-5053; 1678-4790
• DOI: 10.1590/S0103-50532012000500023

Laser-induced breakdown spectroscopy (LIBS) was employed in the study of two fragments of prehistoric rock wall paintings found at two Brazilian sites: in Piauí State (Toca Extrema II) and in Rio Grande do Norte State (Xique-Xique). A time-resolved echellebased LIBS system assembled in the laboratory (laser Nd:YAG, 1064 nm, 5.2 ns) was employed for spectral acquisition. Preliminary depth profile studies were carried out in surrogate samples of a multilayer painting on wood to determine the best energy for the laser pulse. For each fragment of wall painting, the depth profile composition was investigated by firing 8 successive laser shots at each of 16 locations (8 in the area of pigment and 8 in the area of substrate). It is demonstrated in this work that the use of multivariate techniques is compulsory due to the high complexity of the spectral data obtained from depth profile studies of the archaeological samples.