ABSTRACT
Ultramarine blue pigment, one of the most valued natural artist's pigments, historically was prepared from lapis lazuli rock following various treatments; however, little is understood about why or how to distinguish such a posteriori on paintings. X-ray absorption near-edge structure spectroscopy at the sulfur K-edge in microbeam and full-field modes (analyzed with nonnegative matrix factorization) is used to monitor the changes in the sulfur species within lazurite following one such historically relevant treatment: heating of lapis lazuli before extracting lazurite. Sulfur signatures in lazurite show dependence on the heat treatment of lapis lazuli from which it is derived. Peaks attributed to contributions from the trisulfur radical-responsible for the blue color of lazurite-increase in relative intensity with heat treatment paralleled by an intensified blue hue. Matching spectra were identified on lazurite particles from five historical paint samples, providing a marker for artists' pigments that had been extracted from heat-treated lapis lazuli.
ABSTRACT
One of the most fascinating objects in the Rijksmuseum (Amsterdam, The Netherlands) is an early 16th century prayer nut. This spherical wooden object measures 4 cm in diameter and consists of two hemispheres connected with a small hinge so that it can be opened. The interior of the nut holds wood carvings with scenes from the life of Christ. These miniature reliefs show an incredible degree of finish with carving details well beyond the millimetre scale. In the present paper it is shown how synchrotron-based computer X-ray tomography revealed the structure and fabrication method of the bead. The central part of the relief was cut from a single piece of wood, rather than assembled from multiple components, underlining the extraordinary manual dexterity of its maker. In addition, a piece of fibrous material contained in the inner structure of the bead is revealed. This may have served as a carrier for an odorous compound, which would be in line with the religious function of the prayer nut.
Subject(s)
Materials Testing/methods , Nuts/ultrastructure , Religion , Sculpture , Synchrotrons , Tomography, X-Ray Computed/methods , NetherlandsABSTRACT
X-ray radiography is a common tool in the study of old master paintings. Transmission imaging can visualize hidden paint layers as well as the structure of the panel or canvas. In some medieval altarpieces, relics seem to have been imbedded in the wooden carrier of paintings. These are most probably thin organic fibrous materials such as paper or textile, which in traditional radiography are shadowed by the more absorbing surrounding material. This paper studies the application potential of synchrotron-based tomographic and laminographic imaging complemented with phase-contrast imaging for detection of such relics. The techniques are applied to a dummy painting. The results demonstrate that by using these imaging methods it is possible to three-dimensionally visualize hidden cavities in panels and detect thin fibrous low-Z materials sandwiched between a high-Z paint layer and a thick wooden panel.