X-ray fluorescence in Member States: Argentina. Identification of inorganic components and lipids in a rock art sample from Alero Hornillos 2 (Jujuy, Argentina) by XRF, FT-IR and GC-MS

Full text: Archaeological samples are very complex in terms of composition since they generally consist of a mixture of materials exposed to deterioration factors that are largely dependent on the environmental conditions. Therefore, the integration of analytical tools such as TXRF, FT-IR and GC-MS can maximize the amount of information provided by the sample. Recently, two rock art samples of black camel figures at a Hornillos 2 cave, an archaeological site located 20 km from the town of Susques, Jujuy Province, Argentina at 4020 m above sea level were investigated. The purpose of the present work is to analyze the inorganic and organic components of the samples in order to improve understanding of the artistic practices and technological knowledge of the early inhabitants of this region. Considering the small amount of sample available for the study, TXRF technique was selected for characterization of inorganic components. Analysis by TXRF showed the presence of manganese among others elements, consistent with manganese dioxide for the black pigment. Aiming at the detection of any residual organic compounds, the sample was extracted with a chloroform/methanol (2:1) mixture and the extract was analysed by FT-IR, showing the presence of bands at 2970-2870, 1729 and 1450-1380 cm-1, attributable to lipids. Analysis by GC and GC-MS of the carboxylic acid methyl esters prepared from the sample extract, indicated that the main organic constituents were saturated (C15:0, C16:0, C17:0 and C18:0) and unsaturated (C16:1 and C18:1) fatty acids, together with hydrocarbons of 22, 23, 24 and 25 carbons and one sterol. This composition suggests the use of lipids of vegetable origin as binders. This study shows the advantage of the combination of analytical tools to generate full information on the cultural heritage objects. (author)