Modeling the Evolution of Crosslinked and Extractable Material in an Oil-Based Paint Model System

The construction of mechanistic models for the autoxidation of fatty acid or ester substrates found in oil paint binders is a challenging undertaking due to the complexity of the large crosslinked species that form, and the small molecules that volatilize. Building models that capture this product diversity are made possible by automating the process of network generation. This work presents a microkinetic model for the autoxidation of ethyl linoleate catalyzed by cobalt(II) 2-ethyl hexanoate. The mechanism size was controlled by using a rate-based criterion to include the most kinetically relevant reactions from among the millions of possible reactions generated. The resulting model was solved and compared to experimental metrics. Quantities such as hexanal production and the consumption of unsaturated moieties were in good agreement with experiment. Finally, the model was used to explore the effect of the catalyst concentration and temperature on key measurables.

The Colors of Keith Haring: A Spectroscopic Study on the Materials of the Mural Painting Tuttomondo and on Reference Contemporary Outdoor Paints

To date, little attention has been given to the scientific investigation of modern and contemporary mural paintings. This paper reports on: (1) the in situ spectroscopic analyses of the mural Tuttomondo (1989) painted by Keith Haring (1958-1990) in Pisa (Italy); and (2) the laboratory characterization of acrylic paints produced by Caparol Italy GmbH & Co., the original supplier of paint materials to the artist for the mural. Ultraviolet (UV), visible (Vis), and near-infrared (NIR) fiber optic reflectance spectroscopy (FORS) measurements were carried out in situ. The Caparol paint samples were characterized using benchtop instrumentation including both dispersive and Fourier transform Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR; with sample pre-treatment to remove filler interference in the fingerprint region), and UV-Vis-NIR FORS. This combined analytical approach confirmed that the materials used by Haring for the mural Tuttomondo have the same composition of the new Caparol acrylic paints, except for the case of the yellow pigment. This information offers valuable documentation for the materials history and for the conservation of a mural painting that is considered the last great public work by Haring.

Near-infrared surface-enhanced Raman spectroscopy (NIR-SERS) for the identification of eosin Y: theoretical calculations and evaluation of two different nanoplasmonic substrates

This work demonstrates the development of near-infrared surface-enhanced Raman spectroscopy (NIR-SERS) for the identification of eosin Y, an important historical dye. NIR-SERS benefits from the absence of some common sources of SERS signal loss including photobleaching and plasmonic heating, as well as an advantageous reduction in fluorescence, which is beneficial for art applications. This work also represents the first rigorous comparison of the enhancement factors and the relative merits of two plasmonic substrates utilized in art applications; namely, citrate-reduced silver colloids and metal film over nanosphere (FON) substrates. Experimental spectra are correlated in detail with theoretical absorption and Raman spectra calculated using time-dependent density functional theory (TDDFT) in order to elucidate molecular structural information and avoid relying on pigment spectral libraries for dye identification.

Identification of organic colorants in fibers, paints, and glazes by surface enhanced Raman spectroscopy

Organic dyes extracted from plants, insects, and shellfish have been used for millennia in dyeing textiles and manufacturing colorants for painting. The economic push for dyes with high tinting strength, directly related to high extinction coefficients in the visible range, historically led to the selection of substances that could be used at low concentrations. But a desirable property for the colorist is a major problem for the analytical chemist; the identification of dyes in cultural heritage objects is extremely difficult. Techniques routinely used in the identification of inorganic pigments are generally not applicable to dyes: X-ray fluorescence because of the lack of an elemental signature, Raman spectroscopy because of the generally intense luminescence of dyes, and Fourier transform infrared spectroscopy because of the interference of binders and extenders. Traditionally, the identification of dyes has required relatively large samples (0.5-5 mm in diameter) for analysis by high-performance liquid chromatography. In this Account, we describe our efforts to develop practical approaches in identifying dyes in works of art from samples as small as 25 microm in diameter with surface-enhanced Raman scattering (SERS). In SERS, the Raman scattering signal is greatly enhanced when organic molecules with large delocalized electron systems are adsorbed on atomically rough metallic substrates; fluorescence is concomitantly quenched. Recent nanotechnological advances in preparing and manipulating metallic particles have afforded staggering enhancement factors of up to 10(14). SERS is thus an ideal technique for the analysis of dyes. Indeed, rhodamine 6G and crystal violet, two organic compounds used to demonstrate the sensitivity of SERS at the single-molecule level, were first synthesized as textile dyes in the second half of the 19th century. In this Account, we examine the practical application of SERS to cultural heritage studies, including the selection of appropriate substrates, the development of analytical protocols, and the building of SERS spectral databases. We also consider theoretical studies on dyes of artistic interest. Using SERS, we have successfully documented the earliest use of a madder lake pigment and the earliest occurrence of lac dye in European art. We have also found several examples of kermes and cochineal glazes, as well as madder, cochineal, methyl violet, and eosin lakes, from eras ranging from ancient Egypt to the 19th century. The ability to rapidly analyze very small samples with SERS makes it a particularly valuable tool in a museum context.

Matisse to Picasso: a compositional study of modern bronze sculptures

Inductively coupled plasma-optical emission spectroscopy (ICP-OES) was used to determine the bulk metal elemental composition of 62 modern bronze sculptures cast in Paris in the first half of the twentieth century from the collections of The Art Institute of Chicago and the Philadelphia Museum of Art. As a result, a comprehensive survey of the alloy composition of the sculptures of many prominent European artists of the early twentieth century is presented here for the first time. The sculptures in this study consist of predominantly copper with two main alloying elements (zinc and tin). By plotting the concentrations of these two elements (zinc and tin) against each other for all the sculptures studied, three clusters of data become apparent: (A) high-zinc brass; (B) low-zinc brass; (C) tin bronze. These clusters correlate to specific foundries, which used specific casting methods (sand or lost wax) that were influenced by individual preferences and technical skills of the foundry masters. For instance, the high-zinc brass alloys (with the highest levels of tin and zinc and the lowest melting temperature) correspond to most of the Picasso sculptures, correlate with the Valsuani foundry, and are associated with the most recent sculptures (post-WWII) and with the lost-wax casting method. By expanding the ICP-OES database of objects studied, these material correlations may become useful for identifying, dating, or possibly even authenticating other bronzes that do not bear foundry marks. Figure.

Chemical fingerprinting of ready-mixed house paints of relevance to artistic production in the first half of the twentieth century. Part I: Inorganic and organic pigments

This study reports the multi-analytical investigation of ready-mixed house paints used by artists such as Pablo Picasso (1881-1973) in the first half of the twentieth century. The pigment composition of paint swatches on four historic paint sample cards from the Art Institute of Chicago reference collection was characterized by thorough screening using Fourier transform infrared (FT-IR) and X-ray fluorescence (XRF) spectroscopies, followed by Raman spectroscopy when necessary. Spectroscopic investigations highlighted the dominance of zinc-based whites, the consistent choice of particular pigments or their mixtures, as well as the avoidance of others to achieve the various hues on the sample cards. Notable findings included the documentation of strong spectroscopic signatures of metal soaps. Given the similarities in composition of early twentieth century artists' and house paints, the results indicate that the identification of house paints in works by Pablo Picasso and others must be based on a combination of parameters rather than the detection of a single chemical marker. Results have been applied to the case study of Picasso's 1935 sculpture Figure (AIC 1988.428), which incorporates direct evidence of the use of house paint by the artist.

Surface-enhanced Raman spectroscopy of dyes: from single molecules to the artists' canvas

This perspective presents recent surface-enhanced Raman spectroscopy (SERS) studies of dyes, with applications to the fields of single-molecule spectroscopy and art conservation. First we describe the development and outlook of single-molecule SERS (SMSERS). Rather than providing an exhaustive review of the literature, SMSERS experiments that we consider essential for its future development are emphasized. Shifting from single-molecule to ensemble-averaged experiments, we describe recent efforts toward SERS analysis of colorants in precious artworks. Our intention is to illustrate through these examples that the forward development of SERS is dependent upon both fundamental (e.g., SMSERS) and applied (e.g., on-the-specimen SERS of historical art objects) investigations and that the future of SERS is very bright indeed.

Identification and characterization of artists' red dyes and their mixtures by surface-enhanced Raman spectroscopy

Silver film over nanospheres (AgFONs) were successfully employed as surface-enhanced Raman spectroscopy (SERS) substrates to characterize several artists' red dyes including: alizarin, purpurin, carminic acid, cochineal, and lac dye. Spectra were collected on sample volumes (1 x 10(-6) M or 15 ng/microL) similar to those that would be found in a museum setting and were found to be higher in resolution and consistency than those collected on silver island films (AgIFs). In fact, to the best of the authors' knowledge, this work presents the highest resolution spectrum of the artists' material cochineal to date. In order to determine an optimized SERS system for dye identification, experiments were conducted in which laser excitation wavelengths were matched with correlating AgFON localized surface plasmon resonance (LSPR) maxima. Enhancements of approximately two orders of magnitude were seen when resonance SERS conditions were met in comparison to non-resonance SERS conditions. Finally, because most samples collected in a museum contain multiple dyestuffs, AgFONs were employed to simultaneously identify individual dyes within several dye mixtures. These results indicate that AgFONs have great potential to be used to identify not only real artwork samples containing a single dye but also samples containing dyes mixtures.

Thin lead sheets in the decorative features in Pavia Charterhouse

The facade of the church of the Pavia Charterhouse, built at the end of the 15th century, shows outstanding decorative features made of different stone materials, such as marbles, breccias and sandstones. Magnificent ornamental elements are made of thin lead sheets, and some marble slabs are inlaid with them. Metal elements are shaped in complex geometric and phytomorphic design, to form a Greek fret in black contrasting with the white Carrara marble. Lead pins were fixed to the back of the thin lead sheets with the aim of attaching the metal elements to the marble; in so doing the pins and the lead sheets constitute a single piece of metal. In some areas, lead elements have been lost, and they have been substituted with a black plaster, matching the colour of the metal. To the authors' knowledge, this kind of decorative technique is rare, and confirms the refinement of Renaissance Lombard architecture. This work reports on the results of an extensive survey of the white, orange and yellowish layers, which are present on the external surface of the lead. The thin lead sheets have been characterized and their state of conservation has been studied with the aid of Optical Microscopy, SEM-EDS, FTIR and Raman analyses. Lead sulphate, lead carbonates and oxides have been identified as decay products.

Noninvasive methods for the investigation of ancient Chinese jades: an integrated analytical approach

This paper reports on an integrated analytical approach for the noninvasive characterization of Chinese nephrite samples, encompassing both geological reference specimens and museum objects. Natural variations induced by cationic substitutions, as well as human-induced alterations such as heating, which both affect color, are the focus of this contribution. Totally noninvasive methods of analysis were used, including X-ray fluorescence spectroscopy, Raman microspectroscopy, visible reflectance spectroscopy and X-ray diffraction; moreover, the feasibility of using a portable Raman spectrometer for the in-field identification of jades has been demonstrated. Fe/Fe+Mg (% p.f.u.) ratios of the jades have been calculated based on hydroxyl stretching Raman bands, which will provide an important addition to similar data that are being collected at major museums in the Western and Eastern hemispheres.

Toward the Definition of Immunosuppressive Regimens With Antitumor Activity

Immunosuppressive therapies associated with organ transplantation produce an increased risk of cancer development. Malignancies are increased in transplant recipients because of the impaired immune system. Moreover, experimental data point to a tumor-promoting activity of various immunosuppressive agents. In this study, we compared the effects of 4 immunosuppressive agents with different mechanisms of action (cyclosporine, rapamycin, mycophenolic acid, and leflunomide) on the in vitro growth of various tumor cell lines and umbilical vein endothelial cells. To varying degrees rapamycin (10 ng/mL), mycophenolic acid (300 nmol/L), and leflunomide (30 micromol/L) highly inhibited the growth of human rhabdomyosarcoma, hepatocellular carcinoma, colorectal carcinoma, and endothelial cells. In contrast, cyclosporine (100 ng/mL) did not affect their growth. Our data suggest that regimens containing rapamycin, mycophenolic acid, or leflunomide, which have both immunosuppressive and antitumor activities, should be preferred in transplant recipients to minimize the risk of tumors.

A key factor in modern protection of historic buildings: the assessment of penetration of water-repellent polymers into porous stone-materials

From the 1960s on, the conservation of monuments and stone masonry has witnessed an increasing use of polymeric products during restoration interventions. Actual penetration depths reached by different polymers within the porous stone matrix are supposed to be key factors in determining the efficacy of the treatments themselves (besides, of course, the chemical-mineralogical nature of the stone and the chemical-physical characteristics of the various polymers). This work presents some preliminary results obtained on specimens of Noto calcarenite treated with various polymeric protective products. Samples were investigated with direct analytical methods (micro-ATR spectroscopy, SEM) in order to assess penetration depths reached by polymers inside the stone while reducing to a minimum the necessary manipulation of specimens. The obtained results highlighted the following trend in penetration depths for the various products tested: siloxane product > partially fluorinated acrylic resin > acrylic resin. Moreover, data obtained allowed to establish direct correlation between long term efficacy of products and relative penetration depths.