Franco Cariati

Spectrochemical characterization by micro-FTIR spectroscopy of blue pigments in different polychrome works of art

Abstract Analytical examination of blue paint samples, taken from different artworks dating from the second century AD until 1960, was carried out using FTIR microspectroscopy (both in reflection and transmission mode, the latter with the aid of a diamond cell) supported by micro-Raman spectroscopy and SEM observations as well as EDX spectrometry. Pigments examined included azurite, Egyptian blue and ultramarine blue, either natural or artificial. Characteristic spectra for each pigment are presented and an account for the principal differences observed is given. In particular, the FTIRs capability of probing single pigment grains on the surface of paint cross-sections, when integrated with a microscope, brought to light frequency differences and orientation behaviour of the bands of the various minerals used as painting materials. Indeed, a striking effect of shifting and variation of intensity of some of the bands of azurite and Egyptian blue was noted and related to polarization phenomena occurring when the incident light stroke differently oriented faces of the single pigment crystals. The effects of different mineralogical composition of the semi-precious stone lapis-lazuli (from which ultramarine blue is derived) on the appearance of the spectrum of the pigment are also discussed. Finally, a means of distinguishing the natural from the artificial ultramarine blue pigment, on the basis of their FTIR spectra, is proposed.

Heterogeneous distribution of metal nanocrystals in glazes of historical pottery

It has been recently shown that lustre decoration of medieval and renaissance pottery consists of silver and copper nanocrystals, dispersed within the glassy matrix of the ceramic glaze. Lustre surfaces show peculiar optical effects such as metallic reflection and iridescence. In many cases, lustre appears overlapped to colored drawings. Here we report the findings of a study on glazes, pigments and lustre of several shards belonging to Deruta and Gubbio pottery of XVI century. The components of glazes and pigments have been identified. Lustre is confirmed to be characterised by silver and copper metal nanocrystals inhomogeneously dispersed in the glassy matrix of the glaze. In the case of lustre overlapped to colored decorations, we found two contradictory cases. The first consists of a lustre surface successfully applied over a blue smalt geometrical drawing. The second consists of a lustre surface, unsuccessfully applied over a yellow lead-antimonate pigment. The yellow pigment hinders the formation of lustre and removes crystals of tin dioxide, normally present in the glaze as opacifier.

Determination of the quadratic hyperpolarizability of trans-4-[4-(dimethylamino)styryl]pyridine and 5-dimethylamino-1,10-phenanthroline from solvatochromism of absorption and fluorescence spectra: a comparison with the electric-field-induced second-harmonic generation technique

For fluorescent compounds, the combined use of absorption and emission solvatochromic data allows to estimate indirectly the cavity radius of the molecule in solution, a very critical parameter in the application of the solvatochromic method for the determination of the quadratic hyperpolarizability beta of dipolar molecules. For two test compounds, trans-4-[4-(dimethylamino)styryl]pyridine (DASP) and 5-dimethylamino-1,10-phenanthroline (DAPHEN), the beta values so obtained are compared with those obtained by the EFISH (Electric Field Induced Second-Harmonic generation) technique. For DAPHEN, the versatility of the method described in this work in the presence of more than one electronic transition contributing to the non-linear optical response is demonstrated.

Calcium oxalate films on stone surfaces: experimental assessment of the chemical formation

Abstract This work considers the possibility that calcium oxalate found on stone artifacts has been formed after the oxidation of organic substances applied on the surface of the stone. Laboratory tests, performed with hydroxyl radical as oxidant, seem to support this hypothesis. The organic compounds subjected to the tests were chosen from those used in the past for the conservation treatment of works of art. Both whewellite and weddellite have formed, depending on the organic substance. Fourier transform infrared (FTIR) and X-ray diffraction (XRD) spectra provide the necessary experimental evidence.

Characterization of ancient magnesian mortars coming from northern Italy

Abstract Different ancient mortar samples were analyzed to characterize their binder fraction. Thermal analyses (TG, DSC) proved to be very useful in the identification of three different species of lime composed of: (a) only calcite; (b) calcite and magnesite; (c) calcite, hydromagnesite and magnesite. The hydromagnesite is well identified in the DSC curve showing the peaks corresponding to the three-step thermal decomposition. Also the same mineral was detected by FTIR and/or micro-FTIR analyses, depending on its amount in the binder fraction of the mortar. Actually, the two absorption peaks characteristic of the hydromagnesite were often hidden by the wider peaks due to the asymmetric stretching of the carbonate ion, observed for the calcite and magnesite.

Trianionoeptakis(triarylphosphine)undecagold cluster compounds

Abstract We report on the preparation of compounds of general formula Au 11 L 7 X 3 (L=tris- para substitutedphenylphophine, X=I − , SCN − , CN − ) containing metal-metal bonds.

Identification of pigments on a XV century illuminated parchment by Raman and FTIR microspectroscopies

Abstract The pigments used to illuminate a precious, richly decorated XV century document on parchment, the property of the State Archives of Milan, have been thoroughly investigated by the complementary use of Raman and reflectance Fourier transform infra red (FTIR) microspectroscopies, both performed non-destructively and in situ. The palette has been determined and the pigments used unambiguously characterised. These were all natural mineral pigments: azurite, ultramarine blue, malachite, vermilion and minium. The advantages and disadvantages of each technique, with respect to the identification of single pigments, are discussed, especially in the cases of malachite and ultramarine blue.

A new approach for archaeological ceramics analysis using total reflection X-ray fluorescence spectrometry

Abstract The purpose of this study is to investigate the use of a new quantitative analysis method in case total reflection X-ray fluorescence (TXRF) is applied to archaeological ceramics. This method is alternative to and simpler than traditional TXRF quantitative analysis or typical techniques of elemental analysis such as atomic emission and absorption spectrometry (AES and AAS) which implies the chemical digestion of the sample. A new procedure which allows to obtain an homogeneous sample has been successfully applied. This way it was possible to obtain quantitative results for the elements present in the sedimentation obtained from a suspension prepared with the ceramic sample, by resorting to addition of an internal standard. The archaeological ceramic shards have been also chemically digested and analyzed by inductively coupled plasma-atomic emission spectrometry, AES with flame atomization and electrothermal atomic absorption spectrometry. The quantitative data obtained by means of both TXRF, AAS and AES were compared and worked out by multivariate statistical techniques, such as principal components analysis and hierarchical cluster analysis in order to achieve information concerning pottery provenance.

Micro-Raman identification of the palette of a precious XVI century illuminated Persian codex

Abstract A remarkable, richly decorated Persian manuscript dating from 1537 was investigated by Raman microscopy in order to assess the nature of the pigments used. Although the decorated area measures just a few tens of cm 2 and doesn’t include any anthropomorphic motif, but consists in a very geometric, lacework-like decoration, it contains very elaborate and precious details. A very rich palette was revealed, showing extensive use of the extremely valuable and costly pigment lapis-lazuli, gold and orpiment, besides malachite, vermilion and red lead. With the exception of the choice for an expensive pigment such as lapis-lazuli even for the background, the experimental data confirm that the art of miniature making, as well as the painting materials used in the Middle East, didn’t actually differ much from what is considered to be the acknowledged practice for western art in the same period.

Co-ordination bond properties in phthalocyaninatometal(II) complexes. Part 1. Stereochemistry and bond properties in bis(4-methylpyridine)-phthalocyaninatometal(II)–4-methylpyridine (1/2)(metal = cobalt or iron)

A comparison between the vibrational properties and stereochemistry of [Co(pc)(4Me-py)2] and [Fe(pc)-(4Me-py)2][pc = phthalocyaninato(2 –), 4Me-py = 4-methylpyridine] is carried out by using far-i.r. spectroscopy and X-ray diffractometry. The crystals of the two complexes, based on the packing of [M(pc)(4Me-py)2] adducts and solvated 4Me-py molecules, are isostructural and their orthorhombic unit cells (space group Pbca) have the following parameters: M = Co, a= 10.395(1), b= 25.069(3), c= 17.992(2)A, 1 503 unique observed reflections, final R 0.061; M = Fe, a= 10.315(1), b= 25.006(3), c= 17.876(2)A; 2 950 unique observed reflections, final R 0.063. All the findings lead to the conclusion that structural results and bond properties are strictly related in these complexes. The vibrational M–N(pc) parameters are much more affected than the corresponding structural parameters by differences in the electronic structures of cobalt and iron. In the case of axial M–N(4Me-py), however, the bond length depends strongly on the metal and its value (2.322 A for M = Co and 2.040 A for Fe) is a clear indication of the localization of the unpaired electron in the dz2 orbital of the cobalt complex. The importance of dπ→π*(pc) back donation is shown by the significant difference between the average values of the ‘internal’ and external C–N bond lengths in the macrocycle.