Imaging Secondary Ion Mass Spectrometry of a Paint Cross Section Taken from an Early Netherlandish Painting by Rogier van der Weyden

Abstract

Static secondary ion mass spectrometry (SIMS) is introduced as an analytical technique for the examination of paint cross sections to obtain simultaneous information about the nature and distribution of pigments and the binding medium from a single sample. A sample taken from the virgin's blue robe in the panel painting The Descent from the Cross (Museo del Prado, Madrid) of the Early Netherlandish painter Rogier van der Weyden (1399/1400-1464) was selected for investigation. Data were compared with reference compounds and reference lead white linseed oil paint and egg tempera paint. The static SIMS technique gave position-sensitive mass spectra that were used to image the elemental distribution of pigments and the molecular signature of components of the oleaginous binding medium. SIMS ion images of sodium and aluminum superimposed with the blue pigment ultramarine and those of copper, lead, and calcium with the position of the mineral pigments of azurite, lead white, and chalk, respectively. Preserved monocarboxylic acids of palmitic and stearic acids present as fatty acids and fatty acid lead soaps pointed to the use of linseed oil as a binding medium. Images from the oleaginous binding medium fatty acids show a correlation with the three main paint layers. The observed palmitic/stearic acid ratios for the two ultramarine layers and azurite layers are 1.3, 1.4, and 1.8, respectively. Fatty acids and fatty acid soaps show highest ion yields near lead white, a mineral pigment that serves as a natural chemical drier and is proposed to act as a template for the initial grafting of the polyunsaturated triglycerides of the linseed oil. Almost no fatty acids were detected in other layers visible by light microscopy. The fatty acid lead soaps point toward a mature ionomeric oil paint system that developed over centuries. SIMS evidence for egg tempera, still used in the 15th century, is not detected in the paint cross section. SIMS images correlate well with SEM/EDX, FT-IR and light microscopic images and the SIMS spectral data additionally support the identification of pigment particles, lead soaps, and other binding medium components.

Applications of SIMS to cultural heritage studies

“…The presence of a fatty lead soap points furthermore to a mature oil containing medium. No evidence could be obtained for the presence of egg tempera [11].…”

“…This capability has been demonstrated in work by the research group at AMOLF [10][11][12][13] for the study of paint cross sections. Microscopic and molecular information about the nature and the distribution of pigments and binding media contributes to the answering of technical art historical questions, such as the deduction of the original appearance of the painting, and the establishment of the chemical and physical conditions before conservation and restoration [10].…”

“…As an example Keune and Boon [11] studied a cross section taken from the Virgin's blue robe in the panel painting ''The descent from the Cross'' (Museo del Prado, Madrid) by the Nederlandish painter Rogier van der Weyden (1399/1400-1464). The aim was to address the question of to what extent oil and century egg tempera were used together as binding medium in 15th century paintings.…”

Identification of Different Copper Green Pigments in Renaissance Paintings by Cluster-TOF-SIMS Imaging Analysis

“…The aim of this research is to use time-offlight secondary ion mass spectrometry (TOF-SIMS) imaging using cluster primary ion beams to identify and locate this copper green pigment, with a spatial resolution and surface sensitivity that is not achievable by conventional techniques, e.g., infrared spectroscopy. Indeed, for nearly 6 years, cluster TOF-SIMS has become a technique of choice to study stratigraphic materials in Cultural Heritage [13], and especially paintings, for the simultaneous location and identification of hybrid materials [14][15][16].…”

Feasibility of analyzing molecular pigments in paint layers using TOF S–SIMS

“…It therefore represents one of the few methods capable of closing the traditional gap between the fields of organic and inorganic analytical chemistry. This capability has been demonstrated in work by the research group at AMOLF [10][11][12] for the study of paint crosssections.…”