Testing of Raman spectroscopy as a non‐invasive tool for the investigation of glass‐protected pastels

Abstract

Five French pastels and a sanguine drawing dating from the 17th to the 20th century were studied by Raman spectroscopy. Different operative conditions were used: the pastels were investigated through their protective glass, and the results obtained were compared with those obtained after removing the glass and after sampling a micrometric particle of pigment. Different parameters (wavelengths, powers of excitation and objectives) were tested in order to assess the optimal procedure of analysis for this fragile work of art. The results obtained for black (carbons), yellow (chrome/cobalt yellow), red (lead oxide, vermillion, orpiment), brown (red lead and chrome yellow), blue (Prussian blue, lapis lazuli/ultramarine), green (mixture of above blue and yellow pigments) and white (calcite, lead white, anatase) pigments are presented and the consistency of the pigments' period of use with the dating proposed for each pastel is evaluated. In one of the pastels, the blackening of the carnation colour made of an unstable mixture of lead white, red lead and vermilion was studied.

Testing of Raman spectroscopy as a non‐invasive tool for the investigation of glass‐protected miniature portraits

“…The 200× objective also helps in decreasing the fluorescence background, as aleady observed in the analysis of pastels. [11] Even though its NA is only 0.62, the 200× objective ( Fig. 9) led to a decrease of the fluorescence background due to the ivory substrate under green laser excitation; this can be related to a better focusing along the z-direction through the protective glass than achieved with the 0.76 NA 50× objective.…”

“…Pastels, [11] like miniatures, are rarely varnished. This leaves the paint layer exposed to dirt and pollutants, necessitating the use of a glass cover.…”

“…Raman spectroscopy is now widely used in the analysis of pigments, mainly by sampling, [10 -16] and recent identifications have been carried out directly on pastels through their glass cover. [11] The identification of pigments can be considered as a marker for a certain date, useful for glass, ceramic or enamelled metal objects. [10,11,17 -23] Up to the early 18th century, most of the pigments used were minerals with well-known spectral signatures.…”

Lacquerware Pigment Identification with Fixed and Mobile Raman Microspectrometers: A Potential Technique to Differentiate Original/Fake Artworks

“…The second half of the 19 th and the whole 20 th centuries are characterized by the emergence of many new and patented pigments (phthalocyanines, alizarin, etc.) offering a large choice to artists and craftsmen [5][6][7][8][9][10]. Pigments and specific mixtures by which sometimes they were commercialized can be used to trace given periods of production.…”

“…Pigments and specific mixtures by which sometimes they were commercialized can be used to trace given periods of production. Therefore identification of specific pigments in artwork can be used for dating purposes, as was already demonstrated for paintings, glass, ceramic or enameled metal objects [1,3,[5][6][7][8][9][10][11][12][13][14][15][16][17][18]. Their presence of certain pigments may indicate a restoration, later embellishment or identify a fake or a modern replica.…”