Earth pigments in painting: characterisation and differentiation by means of FTIR spectroscopy and SEM-EDS microanalysis

Abstract

Analytical characterisation of natural earths (ochres, siennas, umbers and green earths) has been carried out using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) coupled to an energy dispersive X-Ray spectrometer (EDS). The study of these pigments, which are found in works of art, is very important since it can shed light on their source or the pictorial technique used. FTIR spectroscopy is suitable for the identification and differentiation of ochres and siennas. According to the matrix of the sample, FTIR allows the classification of ochres into ochres containing kaolinite and ochres containing sulphate. One of the goals of this research has been to establish a relationship between the matrix and the source of the samples tested. SEM-EDS is probably a better technique than FTIR for characterising umbers and green earths since they do not exhibit significant differences when FTIR studies are performed.

Sub-micron proximal probe thermal desorption and laser mass spectrometry on painting cross-sections

“…The fact that signal from spots 2 and 1 can be detected on the second pass demonstrates that complementary analytical techniques can be performed on the same sample spot more than once. Following successful application to the well-characterized 5 caffeine system, the AFM-TD technique was next applied to more challenging samples -a traditional organic colorant and modern synthetic pigments prepared as mounted cross-sectionsin order to determine whether the overall approach is reasonable for samples of these types. Analogous non-resonant laser ionization experiments with standard alizarin crimson dye (without the AFM-TD step) were performed to determine whether additional fragments were 25 created in the AFM-TD heating step.…”

“…19 We further extend this combination of AFM proximal probe AFM-TD and MS by decoupling the AFM step from the MS step. In our approach we collect sub-micron size samples 5 through AFM proximal probe AFM-TD, followed by separate analysis with resonant two photon ionization (R2PI) coupled with mass spectrometry. While ESI-MS is well suited for mass spectrometry of unknown compounds, R2PI can identify and selectively ionize specific molecules.…”

“…20 The sample bar is loaded into a high vacuum chamber, where it is positioned directly in front of a pulsed nozzle. The sample bar can be translated for successive laser 5 shots on different locations. Material is laser desorbed from the sample bar by light from a Continuum MiniLite 1064 nm Nd:YAG laser, which is attenuated to minimize fragmentation and focused to a slit approximately 1 × 5 mm, within 5 mm of the nozzle.…”

Integrated analytical study for the authentication of five Russian icons (XVI–XVII centuries)

“…The presence of these impurities (clay minerals based on Al and Si elements) corresponds to what is referred to in the literature as the use of white earths based on kaolinite in grounds and priming layers for post-Byzantine icons (Genestar and Pons, 2005;Hradil et al, 2003). The identification of gypsum (known as ''levkas'' in Russian language) in the preparation of all five icons confirmed the assessment in the literature concerning the traditional use of this charge in ancient icon painting (Daniilia et al, 2002;Lobefaro, 2003;Matteini and Moles, 1989;Sandu et al, 2006a,b).…”

“…10). The FTIR spectrum of sample 2S2 indicates for the same yellowcolored layer, the presence of silicatic components, identified by a broad band between 800 and 1150 cm 21 (Genestar and Pons, 2005).…”