Pigment Identification and Depth Profile in Pictorial Artworks by Non-Invasive Hybrid XRD-XRF Portable System

Abstract

A non-invasive XRD-XRF portable system for Archaeometry based on Angle and Energy Dispersive XRD (Hybrid XRD) plus XRF has been previously proposed by the authors. It gathers an attractive compromise between analytical performance and measurement time, as well as a higher energy penetration with respect to conventional Angle Dispersive XRD (ADXRD). Penetration to inside layers, usually perceived as an inconvenient for non-invasive portable XRF or XRD analyzer, can instead be informative for the proposed hybrid XRD-XRF system to perform depth profiling analysis. This hybrid configuration harness from the redundancy of the data, in the sense that a single XRF or XRD specimen, taken at the same sample point, appears in multiple spectrograms to account for data counting statistics. On this work, the performance of the system on standard reference material, as well as the identification of pigments in the surface layer of paintings is evaluated. Specific Hybrid data processing was conceived to examine the layer structure of the painting, by distinguishing signal patterns of the exposed and the under layers. The system is ventured for the first time to the study of pictorial artworks in coffin and cartonnage samples from ancient Egyptian sarcophagi. Prussian blue pigment in a modeled painting is also discussed.