In situ Raman microscopy applied to large Central Asian paintings

Abstract

Procedures and versatile Raman instruments are described for the non-destructive in situ analysis of pigments in large paintings. A commercial Raman microscope is mounted on a gantry for scanning paintings with dimensions exceeding 1 m 2 . Design principles and the physical implementation of the set-up are outlined. Advantages/disadvantages and performance of the gantry-based instrument are compared with those of a mobile Raman probe, attached to the same Raman microscope. The two set-ups are applied to Central Asian thangka paintings. The utility of the gantry-mounted Raman microscope is demonstrated on a 19th century Buddhist painting from Buriatia, South Siberia. Surprisingly, three arsenic-based pigments, i.e. orpiment, realgar, and pararealgar, are found all in the same painting. Pararealgar is used for painting the numerous yellow areas. Realgar is admixed with red lead for adjusting its orange tint. Finally, orpiment is blended with Prussian blue for producing green. Traditional malachite is used in addition as a non-adulterated green pigment. The mobile Raman probe was employed for examining a Tibetan painting of the 18th century from Derge monastery in the Kham area of Sichuan. The highly unique painting could be dated well and its origin accurately located. In fact, the painter's workshop, where the thangka has been executed, is shown in great detail on the painting itself. The painter's palette of this thangka matches the canonical set of pigments used in Tibet for more than 10 centuries.

Comparing the effectiveness of hyperspectral imaging and Raman spectroscopy: a case study on Armenian manuscripts

“…An area can be mapped simultaneously by defocussing the laser beam, but this greatly reduces the intensity and as such is limited to a field of view on the order of micrometres [30]. In general using Raman spectroscopy as a mapping tool is unusual [31]. XRF has also been used for mapping but is also very slow, with an area of 36 × 34 mm scanned in 45 min in one study [16].…”

Historical Note: Characterization of Pigments and Binders in Mural Painting Fragments from Bezeklik, China

“…Several investigative studies have been carried in the past to document information about the pigments (Burgio,Clark, Rosser-Owen, 2007;Colomban, 2003;Ernst, 2010;Correia et al 2007;Frausto-Reyes et al 2009), the authenticity of the work of art (Clark, 2007) and environmental degradation product (Smith and Clark, 2002). Many of these studies have been carried in-situ in non-invasive techniques (Burgio,Clark, Rosser-Owen, 2007;Colomban, 2003;Ernst, 2010;Correia et al 2007;Frausto-Reyes et al, 2009) while many others have been performed on pigment fragments removed from actual works of art (Correia et al, 2007;Frausto-Reyes et al 2009;Smith and Clark, 2002;Clark and Curri, 1998;Edwards et al 2003). Raman spectra of a large number of natural and synthetic pigments have been studied and the results reported in the form of spectroscopic libraries (Burgio and Clark, 2001;Bell, Clark and Gibbs, 1997).…”

A scientific study of the pigments in the wall paintings at Jokhang Monastery in Lhasa, Tibet, China

“…More recently, Raman microscopy was used in the recognition of pigments in Tibetan paintings. In 2010, Azurite, malachite, red lead, cinnabar, orpiment and gypsum were found in a Tibetan Thangka painting of the 18th century at the Derge Monastery with a mobile Raman probe [6]. Recently, pigment samples from the wall paintings of the 15th century at the Tsokchen Chanting Hall of the Drepung Monastery were identified as cinnabar, iron red, malachite, azurite, orpiment, chalk and carbon [7], while pigments from the Palcho Monastery were identified as cinnabar, iron yellow, malachite, azurite, chalk and carbon [8].…”