Analysis of wax solubility of rubber vulcanizates using wax solution in toluene and molten wax

Wax is commonly used as an antidegradant for rubber materials by formation of an impervious barrier. Wax solubilities in natural rubber (NR), styrene–butadiene rubber (SBR), and butadiene rubber (BR) vulcanizates were measured using wax solution in toluene and molten wax. Wax solubilities using molten wax were much higher than those using wax solution in toluene. The wax solubility of NR vulcanizate was higher than those of SBR and BR. Parameters influencing wax solubility were the solvent swell, rubber fraction and filler type as well as the rubber type. Molecular weight distribution of the dissolved wax was different from that of the raw wax; the dissolved waxes with lower molecular weights were relatively higher than the raw ones. We believe that wax solubility and molecular weight distribution of the dissolved wax can be widely used for determining the wax type and content.     

Techniques of thermal analysis applied to the study of cultural heritage

It is increasingly important that chemistry reaches people who have not studied directly this field of science but that, daily, have practices where chemistry is involved in various extents. This is what happens, for instance, in the activities related with the study and the preservation of cultural heritage. In this sense, the present work is a short review of the particular case of techniques based on the thermal analysis and calorimetry applied within the context of the characterization of art and archeological objects, exemplified by various case studies, as the characterization of mortars, preparatory grounds, ancient painting materials and drying oils.     

Identification of complex structures of paintings on canvas by NMR: Correlation between NMR profile and stratigraphy

Paintings on canvas are complex structures created by superimposing layers of different composition. Investigations on the structure of these artworks can provide essential information on their state of conservation, pictorial technique, possible overpaintings, and in planning a proper conservation plan. Standard methods of investigation consist in sampling a limited number of fragments for stratigraphic analyses. Despite the recognized validity of these methods, they are affected by evident limitations. Nuclear magnetic resonance (NMR) profiling, often named NMR stratigraphy, is an NMR relaxometry technique applied by single-sided portable devices developed to overcome the disadvantages of microinvasive stratigraphic analyses. The potential of this approach on artworks, including wall paintings and a few examples of painted canvas, is described in the literature. In this study, NMR profiles of painting on canvas were examined by analyzing transverse relaxation time data by T₂ quasi-continuous distributions and the results compared with standard stratigraphic cross-sections analysis. Combining signal intensity and T₂ quasi-continuous distributions, the identification of textile, preparatory, and paint layers was enhanced. The diction “NMR stratigraphy” for these inhomogeneous layered artworks is also discussed. Indeed, unlike the stratigraphic cross-sections, NMR profiles provide information on a volume (flat slice), rather than on a surface, and the collected signal can derive from nonuniform and partially overlapping layers. This study paves the way for extensive investigations on relaxation time quasi-continuous distributions in various binder/pigment mixtures in order to improve the reliability of NMR profile as an innovative, non–invasive, and nondestructive method for analyzing paintings on canvas.     

Compact plasma source for removal of hydrocarbons for surface analysis

A low–energy, constricted‐anode Anders‐type plasma source was built and tested for the chemical removal of adventitious carbon on surfaces. Oxygen plasma, generated in the source, extends to the sample surface through an aperture in the anode. This plasma reacts with surface hydrocarbons and removes them in less than a minute without influencing the intrinsic surface stoichiometry of nonoxidizing samples such as minerals, glasses, and metal oxides. Adventitious carbon removal is critical for accurate binding energy determination and quantitative measurements in XPS and AES, particularly in multicomponent materials. We measure the plasma to be composed primarily of O⁺ and O₂⁺, with minor H⁺, H₂⁺, and O⁺⁺ components. Ion energy distributions were measured for O⁺ and O⁺⁺ and show all emitted ions have energies less than 50 eV, confirming chemical desorption as the primary removal mechanism. The plasma source, easily built ‘in house’, is compact and can be mounted on a 2.75‐in flange for in situ specimen cleaning prior to surface analysis. Copyright © 2009 John Wiley & Sons, Ltd.     

1H and 13C NMR spectral assignments of four dammarane triterpenoids from carnauba wax

The phytochemical investigation of carnauba wax led to the isolation of three new dammarane triterpenoids 1, 2 and 4, together with the known triterpene 3. The structures of the new compounds were determined by 1D and 2D NMR spectroscopy and by comparison with published data for closely related compounds.     

How effective are reducing plasma afterglows at atmospheric pressure in removing sulphide layers: Application on tarnished silver,sterling silver and copper

A plasma afterglow from a gas mixture of 5 vol% H₂ in He is able to remove tarnish layers on pure silver in a matter of seconds. This dry, localized, and noncontact cleaning technique is a promising method to clean historical objects where silver is combined with organic materials and where traditional cleaning techniques are not recommended. However, historical objects are often manufactured with silver alloys but somehow their tarnish layers are removed less effectively with plasma treatments. To understand the different impact of the afterglow, the surfaces of corroded silver, sterling silver, and copper coupons are characterized before and after plasma treatment by a multianalytical approach combing optical and confocal microscopy, scanning electron microscopy coupled to energy dispersive X‐ray analysis and chronopotentiometry. The analyses demonstrate that the few hundred nanometre‐thick tarnish layer on pure silver is transformed through the whole thickness resulting in a porous metallic film. On top of that metallic film, some isolated remnant Ag₂S particles are found. For sterling silver, a yellowing of the surface occurs. The Ag‐rich corrosion products are reduced to a large extent, while the Cu‐rich corrosion products are only partially reduced. For corroded copper, no apparent visual change is observed at a macroscopic scale, although the morphology of the surface changed. The results allow an evaluation of the cleaning efficiency and provide a deeper understanding of hydrogen plasma effects on the transformation of sulphide corrosion layers at atmospheric pressure.     

Preparation and analysis of a marble reference material

A 7 kg stone of a Carrara marble was reduced to grains smaller than 100 m, mixed and homogeneized in order to prepare a marble reference material. The homogeneity was tested for 16 elements by instrumental neutron activation analysis (INAA). Through a one-way analysis of variance based on several analyses of each of 15 bottles and within the same bottle, it was concluded that the inter-bottle heterogeneity is not greater than the intra-bottle heterogeneity. Results on the concentration of major and trace elements in the marble reference material, obtained by different laboratories and different techniques, are given. The limestone certified reference material KALKSTEIN KH was used to evaluate measurement accuracy, to intercalibrate laboratories, and to provide compatibility of measurement data.     

White marble from Italy and Turkey: An archaeometric study based on minor-and trace-element analysis and petrography

In 94 marble samples from 4 quarry districts in Italy (Carrara) and Turkey (Proconnesus, Dokimeion, Usak), minor and trace elements were determined by instrumental neutron activation analysis (INAA) and atomic absorption spectrometry (AAS). The maximum size of the calcite grains (MGS) of the rocks was measured in thin section. For 16 elements considered in this work, the concentration ranges show important inter-district overlaps; this also applies to the maximum grain size. However, the application of cluster analysis, using selected attributes, allows one to discriminate every pair of districts; 90 samples are classified correctly in all classification dendrograms.     

Application of microemulsions for the removal of synthetic resins from paintings on canvas

Abstract

Traditional cleaning methods with organic solvents often are not suitable for removal of aged resin so researchers have to find new formulations. In this work, a case study is reported in which new microemulsions were applied on the surface of a painting covered by some aged resin layers used during a previous restoration. Based on the quality of the intervention and the analysis of a sample of the varnish carried out with both MALDI-TOF and ATR-IR spectrometers, it was conjectured that this undesired material could be an acrylic polymer. So it was chosen to use xylene, ethyl acetate and propylene carbonate (XYL and EAPC) microemulsions (O/W oil in water). The first is able to solubilise only acrylic polymers, the second may solve both acrylic and vinyl resins. The first has had the greatest effect allowing complete varnish removal and original artwork restoration.     

How mobile NMR can help with the conservation of paintings

The conservation of paintings is fundamental to ensure that future generations will have access to the ideas of the grand masters who created these art pieces. Many factors, such as humidity, temperature, light, and pollutants, pose a risk to the conservation of paintings. To help with painting conservation, it is essential to be able to noninvasively study how these factors affect paintings and to develop methods to investigate their effects on painting degradation. Hence, the use of mobile nuclear magnetic resonance (NMR) as a method of investigation of paintings is gaining increased attention in the world of Heritage Science. In this mini-review, we discuss how this method was used to better understand the stratigraphy of paintings and the effect different factors have on the painting integrity, to analyze the different cleaning techniques suitable for painting conservation, and to show how mobile NMR can be used to identify forgeries. It is also important to keep in mind its limitations and build upon this information to optimize it to extend its applicability to the study of paintings and other precious objects of cultural heritage.     

Iron stains on paper. Can electrophoretic removal become an effective alternative to chemical cleaning?

Abstract

Research in restoration and conservation is directed vs. more sustainable working materials, methods and technologies. Electrophoretic removal, from porous material, of undesired stains due to charged species is theoretically an interesting alternative to chemical cleaning methods, but the lack of specific and comprehensive research work leads to controversial opinions about the efficiency and the needed harmfulness for the treated objects. In this work paper, samples with artificial rust stains were subjected to electrophoretic cleaning treatments in mineral water as electrolyte. Treatments were carried out either in a bath by complete sample immersion between the distanced electrodes or by sample wetting and sandwiching between the electrodes. Evaluation of cleaning efficiency and treatment effects was based on colour change measurements (image analysis of scanned paper samples before and after the treatment and by colorimetric data via spectrophotometric measurements), investigation of morphological changes by SEM observations and folding endurance measurements.     

Preliminary study of UV ageing process of proteinaceous paint binder by FT-IR and principal component analysis

This work presents a preliminary study on the ageing process of proteinaceous binder materials used in painting under UV light. With this aim, two sets of model samples were prepared: samples prepared using a single protein material and complex samples prepared in a similar way to the sequence of layers in a real painting from lowest to highest complexity (protein, drying oils, pigment and varnish). The study focuses on acquiring information about the possible degradation process of proteinaceous binders due to ageing and how this process be affected by the presence of characteristic non-proteinaceous painting materials, such as lipids from linseed oil, terpenic compounds from varnish and inorganic pigments. Samples simulated the accelerated ageing process, as did the UV light exposition. The FT-IR spectra were recorded after 100, 500, 1000 and 1500 h of exposition. The study of the accelerated ageing process was performed by means of principal component analysis (PCA) using the FT-IR spectra obtained. Loadings from the significant principal components were analysed to find the FT-IR frequency (cm⁻¹) involved in the degradation process. The study showed the lack of any relevant modification on the proteins in the single model samples. On the contrary, the complex model samples showed the ageing process. The accelerated ageing process can be explained by a principal component from PCA. The most affected IR region was 2900-3600 cm⁻¹, where the amide band was included.     

Discovery of mass spectral characteristics and automatic identification of wax esters from gas chromatography mass spectrometry data

The mass spectral characteristics of wax esters were systemically summarized and interpreted through data mining of their standard mass spectra taken from NIST standard mass spectral library. Combining with the rules of retention indices described in the previous study, an automatic system was subsequently developed to identify the structural information for wax esters from GC/MS data. After tested and illustrated by both simulated and real GC/MS data, the results indicate that this system could identify wax esters except the polyunsaturated ones and the mass spectral characteristics are useful and effective information for identification of wax esters.     

The Use of Modified Zr-nPropoxide in the Consolidation of Calcite: A Preliminary Study Focused into the Conservation of Cultural Heritage

The monomeric precursor Zr-npropoxide was modified using chelating agents. The resulting sols were used to compose a consolidant sol that included coupling agents selected based on previous studies done by ourselves, the hydrophobic agent trimethyl methoxysilane (TMS) and mesitylene as drying control chemical additive (DCCA). The sols were studied by Fourier Transform Infrared Spectroscopy (FTIR). In a later stage calcite powder was impregnated with the sols and studied by Diffuse Reflectance Infrared Spectroscopy (DRIFT). According to the DRIFT results new bands appeared, that indicate interactions between the coupling agents and calcite. The Kratky plots obtained from the sols indicate that in all cases fiber-like oligomeric structures were obtained, having a fractal dimension value 1.60.     

NMR study of a novel pentasaccharide isolated from Penicillium citrium

Penicillium citrium produces several fructose oligomers, namely kestose, neokestose, nystose, 1‐furanosylnystose and a novel pentasaccharide. The pentasaccharide consists of four fructoses and one glucose but its structure is different from that of 1‐furanosylnystose. Its complete structure was determined based on various two‐dimensional NMR experiments. Copyright © 2003 John Wiley & Sons, Ltd.     

Probably counterfeit in Roman Imperial Age: Pattern recognition helps diagnostic performed with inductive coupled plasma spectrometry and thermogravimetry analysis of a torso and a head of Roman Age marble statue

This work deals with the attempt to classify marbles, coupling chemometry and two different instrumental techniques, such as inductive coupled plasma atomic emission spectroscopy (ICP-AES) and thermogravimetry analysis (TGA). Chemometrics have been hyphenated, firstly to obtain variables selection on weight loss vs temperature in TGA and after for unsupervised classification of 22 samples (5 ancient marble and 17 single samples from quarries) obtaining a well recognisable classification. The objects in “test set” are the body and the head of one statue and a Torso Virile statue; the “evaluation set” are two well-known ancient finds; the “training set” is constituted by 17 samples coming from marble assigned to Italian, Greek and Turkish quarries.22 elements (Ca, Si, Na, K, Mg Ti, Al, Fe, Pb, Zn, Sr, Zr, Cu, Mn, Rb, Y) are taken into consideration; with TGA 951 values of mass-residual vs temperature are considered. After selection 8 variables from ICP-AES and 4 from TG compose the matrix.We obtain a separation of Italian marbles cluster from marbles of other countries and recognise the different provenience of the body and head and classify the unknown one. This methodology can be applied to classification study of similar ancient artefacts as pottery, ceramics, glass and stones.Counterfeit, or substitution of parts such as head, legs, and hands was a current practice in the late Roman Age, and also in the Renaissance a lot of statues were “rebuilt” with spare parts, so this word describes an historical restoration practice and not just depreciative.     

Elucidation of molecular and elementary composition of organic and inorganic substances involved in 19th century wax sculptures using an integrated analytical approach

Wax sculptures contain several materials from both organic and inorganic nature. These works of art are particularly fragile. Determining their chemical composition is thus of prime importance for their preservation. The identification of the recipes of waxy pastes used through time also provides valuable information in the field of art history.The aim of the present research was to develop a convenient analytical strategy, as non-invasive as possible, that allows to identify the wide range of materials involved in wax sculptures.A multi-step analytical methodology, based on the use of complementary techniques, either non- or micro-destructive, was elaborated. X-ray fluorescence and micro-Raman spectroscopy were used in a non-invasive way to identify inorganic pigments, opacifiers and extenders. The combination of structural and separative techniques, namely infrared spectroscopy, direct inlet electron ionisation mass spectrometry and high temperature gas chromatography, was shown to be appropriate for unravelling the precise composition of the organic substances. A micro-chemical test was also performed for the detection of starch.From this study it has been possible to elucidate the composition of the waxy pastes used by three different sculptors at the end of the 19th century. Complex and elaborated recipes, in which a large range of natural substances were combined, were highlighted.     

Characterization of a heavily corroded bronze statue from Pharaonic Egypt

The current study aims to characterize a heavily corroded bronze statue from Pharaonic Egypt, in terms of the morphology and mechanism of corrosion. The characterization was carried out by a combination of methods, including the scanning electron microscope equipped with energy dispersive X-ray spectroscopy (SEM–EDS), USB digital microscope, X-ray micro-diffraction, and Raman micro-spectroscopy. Insights into the morphology and corrosion mechanisms of two corrosion stages are presented. Specifically, the metallic-wall layer was first converted into grayish-brown corrosion mottled with green and gray spots in the central part, in which a greenish-white corrosion phase was formed in the second stage. The EDS analysis of the greenish-white phase revealed the predominance of tin, copper, oxygen, and carbon and a low chlorine content. The greenish-white phase consisted of four corrosion products: romarchite, cassiterite, malachite, and a small amount of atacamite. The morphology developed upon corrosion was attributed to the selective dissolution and depletion of copper in the central layer, internal oxidation of tin, and conversion of cuprite into malachite. Moreover, the usual bronze corrosion products were formed as a superficial layer on the statue.     

Identification,quantification and Chrastil modelling of wheat straw wax extraction using supercritical carbon dioxide

Supercritical carbon dioxide (scCO₂) can be used as a “green” selective solvent for extractions of wheat straw waxes. For the first time, the crude extraction yields of wheat straw waxes and the yields of a single high value group of components (wax esters) using various scCO₂ conditions (305.15 to 373.15 K and 7.5 to 40 MPa) have been modelled using the Chrastil equation (Chrastil, 1982). The model accurately predicts both the crude yield and percentage of valuable wax esters within the extracts enabling maximum extraction efficiency. The key compounds within the waxes (fatty acids, sterols, fatty alcohols, wax esters, β-diketones and alkanes) have been identified and quantified. This study highlighted that, 14,16 hentriacontanedione was extracted at critical temperature and pressure in concentrations of 1000 μg.g⁻¹ straw. This molecule could demonstrate significant potential as a natural chelate for metal recovery and also in the formation of super-hydrophobic coatings.     

Non-invasive Analysis of Artistic Heritage and Archaeological Findings by Time Resolved IR Thermography

The structure and the preservation state of artistic heritage and archaeological findings have been studied by the analysis of the heat diffusion process in the sample. The investigations have been performed by non-invasive time resolved infrared thermography(IRT). Thickness maps, buried defects detection, inhomogeneity and corrosion analysis, as well as the quality check of welding and reinforcements elements, have been performed on the studied samples. This revised version was published online in July 2006 with corrections to the Cover Date.