Characterisation of materials and techniques in first archaeological findings of Nasca wall paintings

The pre-Colombian wall paintings in Peru were already known from north and central coast sites, but little information exists on the southern coast corresponding to the Nasca region. The recent excavations on Cahuachi site provided fragments of plaster with paint layers found near Great Pyramid, corresponding to phases III and IV of the construction of the site, and dating back to the Early Intermediate Period (from 200 BC to 350 AD). A series of fragments from three locations from these two respective periods were transferred directly from the excavation to the laboratory and analyzed. A panel of observation and analysis methods was applied in order to describe the stratigraphy and materials used for these paintings, with special attention to the paint layer. The stratigraphy was observed by optical and electron microscopies and X-ray fluorescence, Raman and infrared spectroscopies were employed for elemental and molecular characterization of the plaster and paintings. The obtained results show the large presence in painting layers of iron oxides and copper based pigments, as well as calcium sulfate, siliceous clay materials and graphite. Although most of these pigments could be provided by local deposits, the detection of graphite is probably linked to the use of charcoal. The variety of painting materials between phases III and IV are related to the palette of colours and pigments. The colours for phase III seem limited to the red and yellow ochre pigments, and unidentified black and gypsum white. During phase IV, additional pigments were identified such as: paratacamite, malachite and chrysocolla for greens, hematite for purple, charcoal and siliceous white, which replaced gypsum white. The paintings were sometimes applied in several layers and occasionally separated by a white coating layer. The painting materials and techniques identified on Cahuachi site, and especially the differences between the phases observed, constitute a new insight into the knowledge of wall painting tradition in Southern Peru.