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Artistic patination is a traditional colouring technique for metal sculpture, employed by artists in ancient and modern times for aesthetic purposes. Today, knowledge of the artistic value and the chemistry of this superficial chromatic layer, called 'artistic patina', can be successfully acquired through a close collaboration between living artists, foundry artisans, and scientists. Starting from several interviews with the Italian artist Nado Canuti and foundry artisans, specific information was gathered about patination methods and the artist's attitude towards materials restoration. Afterwards, the patinas most used by Canuti were reproduced to study their nature before any ageing or degradation. Their chromatic values, morphologies, and compositions were studied employing a range of techniques such as colour measurements, scanning electron microscopy with energy dispersive X-ray spectroscopy, and micro-Raman spectroscopy. The collected data revealed the formation of main compounds (cuprite, cassiterite, rouaite, chalcocite, isocubanite, and ferroxyhite) and additional compounds (atacamite and CN-containing compound). The scientific results, as well as the artist's statements concerning the patinas' significance, maintenance, and conservation, will contribute towards the future care and preservation of Canuti's sculptures. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Solvent- and water-borne fluoropolymer protective coatings for patina-free bronze discs. • Comparison of rheological, SEM, AFM, electrochemical and spectroscopic measurements. • Potentiodynamic polarisation revealed the improved performance of solvent-borne coatings. • Ex situ IR RA showed that hydration was greatest for the water-borne coatings. • In situ Raman suggested diffusion of lead from bronze alloy. Abstract Solvent- (SB) and water-borne (WB) fluoropolymer coatings were produced for the outdoor protection of bronze. The coatings were prepared from commercially available resins with alternating fluoroethylene/vinylether copolymers. Because any application of protective coatings on works of art requires that they be removable in accordance with conservation ethics, various approaches to achieve removability of coatings were tested. The influence of modifications was verified through comparisons of hydrophobic, compact and irremovable protective coatings. Consequently, we prepared four types of coatings: two SB coatings and two WB coatings. The first SB coating was designed to have a hydrophobic compact structure (SB-c coating), and the second SB coating was modified with the addition of agents that impart strippability (SB-h coating). The same approach was used for the preparation of the two WB coatings: a compact (WB-c) coating vs. a hydrophilic (WB-h) coating, the latter being prepared through the addition of hydrophilic polyisocyanate. The surface properties of the coatings were compared using scanning electron (SEM) and atomic force (AFM) microscopy. WB coatings were found to be more homogeneous in comparison with SB coatings and to have lower surface roughness. Contact angles confirmed the more hydrophobic nature of SB coatings. Potentiodynamic polarisation measurements and accelerated corrosion tests (exposure to acid vapours) revealed that protection efficiency not only increased with thickness but significantly depended on the coating structure. The structure of coatings depended on the rheological parameters of the formulations simulating their behaviour during storage, deposition, and formation of the dry coating. Combined electrochemical and vibrational spectroscopic experiments were used to simulate long-term outdoor exposure of the protective coatings. Ex situ IR RA spectroelectrochemical measurements showed that hydration was more prevalent with WB coatings, and oxidation of bronze at the interface eventually occurred (656 cm−1 band). WB coatings with more free C O groups were more prone to degradation. In situ Raman spectroelectrochemistry confirmed the better protection efficiency of SB over WB coatings. The optical properties of the coatings on glass showed higher transmittance for WB coatings compared to SB coatings. [ABSTRACT FROM AUTHOR]

There is not only one methodology for the study of mineralogical phases in archaeological samples. In this paper, we discuss a strategy applied to ancient iron nail samples completely based on non-destructive analyses. The archaeological samples come from the archaeological site of Valle delle Forme (province of Brescia-Italy) and date back to the 1300-1400 ad. Neutron-based techniques, like time-of-flight neutron diffraction and neutron tomography, have been used to determine the mineralogical composition and the structure of nails. An independent check for the assessment of the presence of different mineralogical phases was given by Raman spectroscopy. The combination of different non-destructive techniques has provided very useful information on their chemical composition, nature of the patina and corrosion features of the nails (also in the bulk of the samples). [ABSTRACT FROM AUTHOR]

We report results of the patina study of underwater archeological finding of medieval copper objects performed by means of the Raman and complementary spectroscopic techniques. The objects were found submerged in the sea as cargo part of the ship which sunk in the Gulf of Gdańsk in 1408. The excavated collection consists of 230 oval ingots of the size and mass up to about 60 cm and 18 kg (total of 2 tons), respectively. In the Raman spectra of the strongly porous ingot encrustation, the bands corresponding to the main patina representatives such as cuprite (Cu2O), atacamite (Cu2(OH)3Cl) and chalcopyrite (CuFeS2), and also chalcocite (Cu2S) and covellite (CuS) are observed and confirmed by the elemental analysis. Raman bands located at 1473 cm−1 and also at 909 and 511 cm−1 are ascribed to the organic Ca-oxalate (whewellite, CaC2O4 · H2O) in agreement with the infrared spectra and surface morphology observed in microscope images. The presence of S, C, Ca, and Fe revealed by the energy dispersive X-ray spectroscopy indicate on patina components resulting from reactions in the microbial environment in seawater and on contributions coming from iron bars, tar, and burnt remains which were also found in the excavated cargo. The results are consistent with literature data on copper ingots from Hungary traded along the south-north route in medieval Europe. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper presents the way we used non-destructive methods-optical microscopy (OM), scanning electron microscopy (SEM) coupled with energy dispersive X-ray analysis (EDX), xray diffraction (XRD) and Fourier-transform Raman (FT-Raman) microscopy. The Raman spectra of copper were reported using an Nd-YAG laser operating at an excitation wavelength of 1064, 785 and 532 nm. These analyses were used to understand the corrosive morphological characteristics of the patina, to investigate the corrosion products, analyze the elementary composition of the copper object and to identify the corrosive factors with effects on the alteration processes. This object exhibited at the museum of the faculty of applied arts, Helwan university-Egypt. The results indicated that the object was made of brass alloy, with copper as the main element, beside zinc. Three layers of alteration products with various composition and morphology covered the substrate of the brass alloy. SEM-EDX, XRD analyses and Raman spectroscopy (RS) revealed the elements Cl, S, O, C, from primary and secondary chemical compounds and from soil micro-structure. This study provides useful information for the conservation of copper object. [ABSTRACT FROM AUTHOR]

Colonisation of wall paintings by microorganisms and other organisms is a well-known problematic phenomenon. Besides taxonomic identification of the biodeteriogen, it is essential to evaluate the consequences of the colonisation, e.g., unsightly coloured patinas. This work proposes new methodology for characterisation of the nature of the main carotenoids and their distribution in brown stains or patinas of a deteriorated wall painting on the north wall of the atrium of Marcus Lucretius House (Pompeii, Italy). Characterisation of the brown patinas and surrounding areas (plaster and polychromy) from the wall painting started with in situ screening using, mainly, a portable Raman instrument with a handheld FTIR (DRIFTS sampling interface) in order to select the sampling areas suitable for further analysis in the laboratory. Two wall painting fragments were then analysed in the laboratory in two steps. First, microscopic observations (SEM and phase-contrast microscopy) were used to determine whether biodeteriogens were present in the samples. In a second step, confocal Raman microscopy (785 and 514 nm excitation lasers) was used to characterise the main biogenic compounds of the brown stains. Because of the resonance Raman effect (514 nm excitation laser), it was possible to obtain reliable Raman features to assign not only the nature of the main biogenic pigments (carotenoids) present in the stains, but also their spatial conformation. Moreover, Raman confocal applications, for example, Raman imaging and depth profiling were also used in a first attempt to determine the distribution of biosynthesised carotenoids in the stains, and to determine the thickness of the brown patinas. [ABSTRACT FROM AUTHOR]

Bronze surfaces suffer from corrosion processes if they are exposed outdoors. They are affected by the presence of different aggressive species, the alloy composition and surface preparation. Bronze can be exposed outdoors non-protected or can be pretreated in different ways. Artists use chemical patinations in order to achieve visual effects. In the present study, different finishes were tested on three different patinas: green nitrate, green chloride and an electrochemically prepared patina. The tested finishes were: imidazole and benzotriazole type inhibitors in either ethanol or Paraloid B44, and Carnauba wax as a representative of waxes. The effectiveness of the applied finishes was examined by electrochemical impedance spectroscopy in a solution simulating urban acid rain. Aging experiments were performed in a climatic chamber and a salt spray chamber in order to combine different exposure conditions, the presence of sulphur dioxide, high humidity and a mist of chloride ions. After immersion in an urban acid rain solution, acidified to pH 5, the different patinas were investigated by SEM/EDX and Raman spectroscopy. [ABSTRACT FROM AUTHOR]

Abstract: The bronze artefacts of cultural heritage are often covered with patina, a layer of corrosion products, which confers their aesthetic and also protects the substrate bronze. Due to the increasing atmospheric pollution these layers are often dissolving when exposed in urban environment. In this work we propose the use of an innoxious imidazole compound as a corrosion inhibitor for patinated bronze. On a Cu–6Sn (wt%) bronze, three types of patinas were synthesized: two by chemical methods (in a sulphate solution and a chloride one) and one by an electrochemical process (in a sulphate/carbonate solution). A blue-green patina was obtained in all three cases, and their morphological and structural characterization was performed by SEM, EDS and Raman spectroscopy. It was found that the sulphate patina is composed essentially of brochantite, the chloride patina of atacamite, and the electrochemical patina of malachite. All three patinas have also a smooth part of surface consisted of cuprite. As corrosion inhibitor 4-methyl-1-(p-tolyl) imidazole was used on all patinas, in a solution of 0.2gL−1 Na2SO4 +0.2gL−1 NaHCO3 acidified to pH 5 which simulates acid rain in urban environment. The results have shown that the inhibitor improves the stability of all three kinds of patinas and can be recommended for protection of works of art. [Copyright &y& Elsevier]

Abstract: The effect of leaching rain on the corrosion behaviour of bronze UNSC83600 was investigated as to the influence of alloying elements (Cu, Sn, Zn, Pb) through dropping tests simulating a severe runoff condition with a solution reproducing natural acid rain. Corrosion was followed with time monitoring both samples and leaching solutions (up to 30 days) by SEM, EDS, Raman spectroscopy, XRD, AAS. The bronze patina behaves as a porous layer enriched in stable tin compounds allowing uniform dissolution of Cu, Zn and partly of Pb. Laboratory results are in good agreement with field studies of outdoor bronzes in unsheltered condition. [Copyright &y& Elsevier]

Abstract: Cultural bronze artefacts are exposed in indoor or outdoor environment. They often suffer of a substantial alteration due to an increasing atmospheric pollution. In this work, we propose the use of some innoxious compounds as corrosion inhibitors of bronze objects covered with patina. The bronze used was Cu–6Sn (in wt.%). This composition was selected after a preliminary work on several archaeological bronzes found in Transylvania, Romania, dated from the Late Neolithic to Roman periods. First, an artificial patina was formed on Cu–6Sn bronze under potential regulation, in 0.2gL−1 NaHCO3 +0.2gL−1 Na2SO4 aqueous solution (pH 8), during 4 days. A pale blue to green patina was obtained and characterized using EDS and Raman spectroscopy. Then, four innoxious organic substances were examined as corrosion inhibitors: 5mM 4-methyl-1-(p-tolyl)-imidazole (TMI), 10mM 1-phenyl 4-methyl-imidazole (PMI), 1mM 2-mercapto 5-R-acetylamino-1,3,4-thiadiazole (MAcT), 1mM 2-mercapto 5-R-amino-1,3,4-thiadiazole (MAT), and for comparison 1mM benzotriazole (BTA). The impedance spectra collected showed, for all of them, three depressed capacitive loops. On the basis of these capacitance values, these loops were allocated to the surface film with ionic conduction, the double layer capacitance with the charge transfer resistance, and the oxidation–reduction process involving the surface patina. TMI and MAcT were found to be efficient inhibitors though their performances are significantly lower than that of BTA. [Copyright &y& Elsevier]

Abstract: Lead patination is a well-known phenomenon that occurs when lead is exposed to the atmosphere. A thin film mainly composed of insoluble lead salts is then formed on its surface, protecting lead against further corrosion. A study of the superficial patination of an ensemble of historical stained glass windows lead cames from different European locations (Belgium, Germany, Holland, Spain and Poland) and different chronologies (from 13th to 20th centuries) is reported in this paper. The main goals of the research were to characterise, both morphological and chemically, the patinas formed on their surfaces and to assess the weathering factors influencing the development of these patinas. Conventional optical microscopy (OM), scanning electron microscopy (SEM) with energy dispersive X-ray microanalysis (EDX) and micro-Raman spectroscopy were used to determine the composition of the patinas. The resulting data have proved to be very useful in establishing the degree of advance of the patination process, which seems to be directly influenced by the environmental conditions to which the lead cames were exposed rather than by chronology of the samples. The results have also provided outstanding data to make decisions in conservation/restoration issues of such historical materials. [Copyright &y& Elsevier]