Use of X-Ray Mapping to Investigate Art Works Before their Restoration

Abstract

Conservation involves the restoration and preservation of museum objects and historical monuments utilising compositional and structural information obtained from modern analytical techniques. The conservation of oil paintings requires an understanding of the individual structure of each work of art. This often involves the need for 1) correct identification of the pigments used by the artist, 2) a detailed knowledge of the chemical interactions between these pigments and 3) an understanding of [1][2][3].SEM/EDS analysis and X-ray mapping (XRM) are excellent tools for characterising the distribution of elements and phases in paint pigments as well as reacted paint pigments. The XRM analytical technique provides an image related to the distribution and relative abundance of elements within a given specimen and thus makes XRM particularly useful for i) identifying the location of individual elements, ii) mapping the spatial distribution of specific elements and iii) determining the reaction product (phases) within a sample [4][5][6]. SEM, X-ray microanalysis and XRM have been used for determination of the above points. Small paint chips were carefully excised from pre-existing damaged regions in each work of art and embedded in polyester resin (Struers Serifix), matching the hardness of an aged oil paint film. These samples were then carefully cross-sectioned with a microtome. The exposed sections were examined by optical microscopy under both incident visible and ultraviolet illumination.Prior to imaging and analysis in the SEM, the microtomed resin blocks containing the cross-section of each paint chip were coated with 30nm of carbon to prevent localised charging under the electron beam, using a Balzers CEA010 carbon thread evaporation attachment connected to a Balzers SCD020 sputter coating unit. Each specimen was analysed using a JEOL 35CF SEM equipped with an Oxford energy dispersive spectrometry (EDS) X-ray detector with a Moran Scientific X-ray analysis and mapping system. SEI and BSE imaging were used to locate individual paint pigments for X-ray analysis. Pigments were then identified using a database of x-ray spectra collected from a broad range of 19 th and 20 th century pigments. Many of the pigments used in this era contained a signature element, which was utilised to map the distribution of each pigment within a given layer.