Discovering Vanished Paints and Naturally Formed Gold Nanoparticles on 2800 Years Old Phoenician Ivories Using SR-FF-MicroXRF with the Color X-ray Camera

Abstract

Phoenician ivory objects (8(th) century B.C., Syria) from the collections of the Badisches Landesmuseum, Karlsruhe, Germany, have been studied with full field X-ray fluorescence microimaging, using synchrotron radiation (SR-FF-microXRF). The innovative Color X-ray Camera (CXC), a full-field detection device (SLcam), was used at the X-ray fluorescence beamline of the ANKA synchrotron facility (ANKA-FLUO, KIT, Karlsruhe, Germany) to noninvasively study trace metal distributions at the surface of the archeological ivory objects. The outstanding strength of the imaging technique with the CXC is the capability to record the full XRF spectrum with a spatial resolution of 48 μm on a zone of a size of 11.9 × 12.3 mm(2) (264 × 264 pixels). For each analyzed region, 69696 spectra were simultaneously recorded. The principal elements detected are P, Ca, and Sr, coming from the ivory material itself; Cu, characteristic of pigments; Fe and Pb, representing sediments or pigments; Mn, revealing deposited soil minerals; Ti, indicating restoration processes or correlated with Fe sediment traces; and Au, linked to a former gilding. This provides essential information for the assessment of the original appearance of the ivory carvings. The determined elemental maps specific of possible pigments are superimposed on one another to visualize their respective distributions and reconstruct the original polychromy and gilding. Reliable hypotheses for the reconstruction of the original polychromy of the carved ivories are postulated on this basis.

Informative Potential of Multiscale Observations in Archaeological Biominerals Down to Nanoscale

“…Additionally, 13 objects kept in the Badische Landesmuseum (Karlsruhe, Germany) could be studied by Full Field Synchrotron micro X-Ray Fluorescence (FF-SR-µXRF) with a new 3D imaging X-ray detector, the Colour X-ray Camera (CXC) at the synchrotron facility ANKA (Karlsruhe, Germany). Full Field-SR-µXRF enabled us to record the elemental distribution of a large area (12.4 × 11.3 mm 2 ) in 2D elemental maps indicating zones of former coloration (Reiche et al 2013). The objects are in general well preserved, apart from some cracks, purple stains, black spots correlated to the deposition of MnO 2 .…”

Non-invasive quantitative micro-PIXE–RBS/EBS/EBS imaging reveals the lost polychromy and gilding of the Neo-Assyrian ivories from the Louvre collection

“…Two-dimensional (2D) mapping techniques have been widely developed over the last few years by scanning the object to be analyzed [1][2][3][4][5][6] or by employing 2D imaging detectors [7][8][9]. These methods are especially useful for the analysis of valuable art or archaeological artifacts requiring non-invasive and spatially resolved chemical analysis of large areas at micro-scale.…”

“…These methods are especially useful for the analysis of valuable art or archaeological artifacts requiring non-invasive and spatially resolved chemical analysis of large areas at micro-scale. Amongst other datasets, information on the manufacturing processes of the objects can be obtained and the original appearance of visually altered objects can be postulated based on chemical analyses [8].…”

“…However, the coloring is no longer visible to the naked eye and colored objects as a basis of comparison are extremely rare for this period. Moreover, analytical data of these objects are limited to our own previous work [8]. Today, only specific alteration phenomena like cracks and discolorations can be observed on the ivory surfaces.…”

“…They can be due to the manufacturing processes or to the destructive effect of the burial environment over time. Punctual analyses by X-ray diffraction (XRD), Raman and micro-particle induced X-ray emission (PIXE) revealed some remaining traces of paints and gilding on the Louvre museum ivories [8,10]. Particularly, purple stains were identified as originating from gold nanoparticles (AuNPs).…”