Characterization of Roman glass tesserae from the Coriglia excavation site (Italy) via energy-dispersive X-ray fluorescence spectrometry and Raman spectroscopy

The combined use of handheld energy-dispersive X-ray fluorescence spectrometry, Raman spectroscopy, and micro-energy-dispersive X-ray fluorescence spectrometry permitted the characterization of Roman glass tesserae excavation from the Coriglia (Italy) archeological site. Analyses of ten different glass colors were conducted as spot analyses on intact samples and as both spot analyses and line scans on select cross-sectioned samples. The elemental and molecular information gained from these spectral measurements allowed for the qualitative chemical characterization of the bulk glass, decolorants, opacifiers, and coloring agents. The use of an antimony opacifier in many of the samples supports the late Imperial phasing as determined through numismatic, fresco, ceramics, and architectural evidence. And dealinization of the exterior glass layers caused by the burial environment was confirmed

Micro-Raman spectroscopy and chemometrical analysis for the distinction of copper phthalocyanine polymorphs in paint layers

In art analysis, copper phthalocyanine (CuPc) is often identified as an important pigment (PB15) in 20th century artworks. Raman spectroscopy is a very valuable technique for the detection of this pigment in paint systems. However, PB15 is used in different polymorphic forms and identification of the polymorph could retrieve information on the production process of the pigment at the moment. Raman spectroscopy, being a molecular spectroscopic method of analysis, is able to discriminate between poly- morphs of crystals. However, in the case of PB15, spectral interpretation is not straightforward, and Raman data treatment requires some improvements concerning the PB15 polymorphic discrimination in paints. Here, Raman spectroscopy is combined with chemometrical analysis in order to develop a procedure allowing us to identify the PB15 crystalline structure in painted layers and in artworks. The results obtained by Linear Discriminant Analysis (LDA), using intensity ratios as variables, demonstrate the ability of this procedure to predict the crystalline structure of a PB15 pigment in unknown paint samples

Investigation of pigment degradation due to acetic acid vapours : Raman spectroscopic analysis

The preservation of moveable cultural heritage objects inside museums includes trying to keep these objects under the best conditions as possible. This is done, amongst others, by controlling the atmospheric conditions under which the objects are preserved: the amount of light, temperature and relative humidity, etc. should be carefully monitored in exhibitions as well as in storage rooms. However, other atmospheric components may as well be important for the optimal preservation of cultural heritage materials, such as acetic compounds derived from wood package. A study of the degradation of malachite, leadwhite, lead-tin yellow type I, red lead and pigment orange 36 is performed using Raman spectroscopy. The degradation of these pigments was analyzed after exposure to acetic acid vapours. Three different acetic acid concentrations in the atmosphere were tested: ca. 150 ppm, ca. 300 ppm and ca. 500 ppm. In all conditions, the relative humidity was kept constant at ca. 75 %. A possible colour change, which can go hand in hand with the degradation process, was evaluated by observing the change of the RGB values of the sample colour. Besides pigment orange 36, which showed to be unreactive towards the acid atmosphere, acetate species were generated for each pigment: malachite reacted towards a verdigris variety; red lead, leadwhite and lead-tin yellow degraded towards lead acetate. At high doses, red lead alters towards a black pigment, which is presumed to be plattnerite