10,420 research outputs found
Corals, pearls and shells in museum collections: micro-Raman spectroscopy for their authentication
No full text
The 20th Century Wall Paintings in the Chapel of the Fallen in Parma Cathedral (Italy): Scientific Investigations for a Correct Conservation Project
No full textIn this work, we present a diagnostic study carried out on 20th century wall paintings in the Chapel of the Fallen of the Great War in the Cathedral of Parma (Italy). The Chapel was painted in the two-year period of 1921–1922 and has been recently restored. The paintings were investigated in order to study the technique used by the painter, Biagio Biagetti (Porto Recanati, 1877–Macerata, 1948) and their state of conservation. A total of twelve micro-fragments of the painting layers were sampled and investigated using different techniques. Raman spectroscopy revealed the large amount of different pigments used for each hue, many of them being synthetic materials. SEM/EDS analysis showed that the mortar was an aerial lime obtained from calcium carbonate mixed with a small amount of clay. Organic materials were identified by FTIR spectroscopy. GC/MS investigations revealed lipid and proteinaceous materials in the examined specimens; the lipid fraction, however, is not attributable to the presence of drying oils. From the determination of the amino acid content, it became apparent that the proteinaceous fraction is due to the combination of egg and animal glue; this allowed us to infer the use of “a secco” techniques, confirming the visual impressions of the restorer. The results obtained have contributed to the definition of the conservation project in its various phases
Micro-Raman investigation of pigments and carbonate phases in corals and molluscan shells
No full textWe report the results of a micro-Raman investigation, in resonance conditions, on the pigments and on the nature of the biogenic carbonate in different species of corals and marine shells of a wide variety of colours. Corallium rubrum (Anthozoa) and Stylaster roseus (Hydrozoa) show calcite and aragonite skeletons, respectively. The shells are mostly aragonitic, with the exception of bivalves of Pectinidae family which reveal a calcite/aragonite distribution.
The main Raman features of the pigments (carotenoids or polyenes) show Raman dispersion (upshift of the C=C (ν1) and C–C (ν2) stretching vibration frequencies of the polyenic chain with decreasing excitation wavelength). Partially or completely demethylated polyenes with different conjugation lengths may be responsible for the colours of Corallium rubrum and of most of the marine shells. Stylaster roseus and the dark brown colours of Gibbula sp (Gastropod class) show typical bands of carotenoids, similar to those found in canthaxanthin.
Overtones and combination bands are described in terms of the four fundamental vibrations of polyenes. A constant ratio between ν1 and ν2 frequencies, nearly independent of the Raman excitation wavelength, has been determined from a large set of data for corals and shells. A simple relationship between the main Raman frequencies and the effective conjugation length N of the polyenic chains is suggested
Nature of pigments in natural and cultured pearls by using Raman spectroscopy
No full textAmong organic gems, pearls are widely used for decorating artworks and precious jewels; due to their attributes of beauty, they are also in high demand in the nowadays gemstone trade.
The nature of color in pearls is still debated, even if recent studies have attributed to mixtures of methylated (carotenoids) or non-methylated polyenes with different UV-VIS absorption spectra and chain lengths [1]. Previous studies have demonstrated the potential of Raman spectroscopy in detecting pigments in cultured freshwater pearls [2].
With the aim to improve knowledge on the nature of pigments in natural and cultured pearls, several pearls species (Japanese cultured saltwater, Chinese natural and dyed freshwater, oriental natural, Tahitian cultured pearls) have been investigated by Raman spectroscopy using several equipment (laboratory set-up vs. portable) and excitation sources (632.8, 532, 473.1 nm).
Colored natural species showed characteristic Raman double peak indicating pigment belonging to the carotenoid family, with C-C (ν2) and C=C (ν1) stretching modes at 1159 cm-1 and at 1516 cm-1. Overtones and combination modes are observed for all species up to > 4000 cm-1 at 473 nm, in resonance conditions. The ν2 and ν1 frequencies depend on the polyene chain length, i.e. on the number N of the conjugated double bonds. The Raman spectra of pinkish pearls may be interpreted on the basis of a mixture of polyene pigments with different chain lengths. A linear relationship between ν1 and ν2 and a simple approximate rule for their dependence on N: ν1 = 254*103/(N+157); ν2 = 189*103/(N+157) has been proposed [1]. On this basis, contributions from N=6 to N=11 may be found by peak deconvolution.
Polyenes have been identified as responsible of color in freshwater and saltwater pinkish and yellowish pearls; finally, in some Chinese freshwater pearls Raman spectra suggested the use of synthetic dyes.
Aknowledgements
The authors are very grateful to the gemmologist Ugo Longobardo for having provided the studied pearls.
References
[1] L. Bergamonti, D. Bersani, D. Csermely, P.P. Lottici, Spectroscopy Letters 2011, 44, 453.
[2] S. Karampelas, E. Fritsch, J.Y. Mevellec, J.P. Gauthier, S. Sklavounos, T. Soldatos, J. Raman Spectrosc. 2007, 38, 217
The nature of the pigments in corals and pearls: a contribution from Raman spectroscopy
No full textRaman measurements at 473.1nm on corals, both calcitic and
aragonitic, and on pearls (aragonitic) were performed to elucidate the nature
of the pigments, with the relative importance of methylated (carotenoids)
or nonmethylated polyenes involved in the color associated with
marine mineralized organisms still being a debated question. The resonance
condition of the laser excitation enables the observation of overtones and
combinations of four main vibrational modes of the polyenic or carotenoid
pigment up to > 5000 cm 1. Raman spectroscopy proves to be a powerful
tool to determine the biomineralized structure, the nature of the pigments,
and the presence of artificial dyes
Correspondence: Laura Kephart and Arthur Stupka
No full textThis 1936 correspondence, between Laura Kephart (Mrs. Horace Kephart) and Arthur Stupka, concerns a possible Kephart Memorial. Horace Kephart (1862-1931) was a noted naturalist, woodsman, journalist, and author and promoter of the Great Smoky Mountains National Park. Arthur Stupka (1905-1999) was the first park naturalist to work at the Great Smoky Mountains National Park
Mindscapes: Laura Riding's poetry and poetics /
No full textTese (doutorado) - Universidade Federal de Santa Catarina, Centro de Comunicação e Expressão.Esta tese propõe uma leitura revisionista da poesia contemporânea através do exame do caso de um dos mais esquecidos escritores norte-americanos do século XX: Laura (Riding) Jackson (1901-1991). O objetivo é demonstrar que Riding não apenas possuía uma poética definida e singular, mas que ela permanece uma das instâncias mais extremas e paradoxais do modernismo anglo-americano, a ponto de Riding abandonar a escrita da poesia em 1938. Recorrendo a conceitos de "formação do cânone" bem como às noções de "discurso" e "função do autor", em Foucault, investigo a construção do cânone da poesia moderna anglo-americana, recuperando o contexto e as circunstâncias da ocultação de Riding. Enquanto cubro os "discursos" poéticos em circulação na primeira metade do século XX-o "imagismo" de Pound, a "dissociação da sensibilidade", "impersonalidade" e "tradição" de Eliot, a "unidade orgância" e "ambigüidade" da Nova Crítica-ofereço um panorama crítico de modernismos alternativos sendo articulados à época. Minha intenção é demonstrar que os poemas de Riding são expressões vigorosas de um escritor para quem "a mente pensando se torna a força ativa do poema", para usar a apta formulação de Charles Bernstein. Entre minhas descobertas sobre as várias e complexas razões que levaram à não-canonização de Riding estão a hegemonia da Nova Crítica, o exílio voluntário de Riding da cena literária (onde são feitas ou desfeitas as reputações), sua recusa em ser antologiada, bem como em ser explicada em termos críticos que não os dela. Todos esses fatores, mais a "dificuldade" de sua poesia, contribuíram para fazer de Riding "a maior poeta esquecida da poesia norte-americana", como escreveu Kenneth Rexroth. Ajudado pelos insights de dois importantes críticos de poesia norte-americana, Charles Bernstein e Marjorie Perloff, defendo que a "poesia da mente" de Riding-onde o que está em jogo é que o que pensamos ser a nossa realidade-representa uma mudança radical no paradigma da poética modernista: de uma poesia centrada na imagem para uma poesia centrada na linguagem. Focalizando a experiência consciente e o tempo duracional do pensamento presente em seus poemas, concluo que as "pensagens" de Riding têm o objetivo preciso de constatar um fato universal: enquanto seres humanos e pensantes, estamos numa condição permanente chamada linguagem
The Polychromatic Inscriptions on the Relief Sculpture <i>Deposition from the Cross</i> by Benedetto Antelami in Parma Cathedral, Italy
No full textThis paper reports on the studies carried out on engraved inscriptions of the Deposition from the Cross by Benedetto Antelami (1150–1230), a relief sculpture conserved in the Cathedral of Parma (Italy). The inscriptions between the characters show residues of colored material in alternating red- and dark-colored stripes. The purpose of this specific investigation was to identify the materials (pigments and organic binders) used for the polychromy that are still present on the relief sculpture. Seven microsamples were taken to carry out laboratory analyses. In red-colored letters, mercury, and sulfur, constituents of the cinnabar (or vermilion) pigment were easily identified by SEM-EDS. This result is confirmed by Raman spectroscopy and XRD measurements. In the dark letters, carbon, iron, and lead are observed. The presence of materials containing metals is compatible with a mastic encrustation technique. FT-IR, Raman, and XRD techniques clearly detect beeswax, which was probably used as a polishing material. Amino acids and lipids that are typical of eggs have been identified by means of GC-MS investigations, suggesting their use as organic components of the mastic encrustation
Preservanti del legno: trattamenti innovativi a base di poliamidoamine e proposta di norma standard per termiti “del legno secco”
No full textIl legno è una risorsa rinnovabile ampiamente usata come materiale strutturale e per una varietà di manufatti, grazie alle proprietà meccaniche particolarmente vantaggiose ed alle caratteristiche estetiche. Tuttavia, a causa della sua natura organica, è soggetto a deterioramento fisico e biologico e in particolare all’attacco di insetti xilofagi come le termiti. È stato sviluppato e brevettato un trattamento innovativo del legno a base di poliamidoamine (PAA) funzionalizzate con silossani, che è stato testato su diversi agenti di biodeterioramento. A livello europeo e italiano, nell’ambito della tecnologia e dei prodotti per la protezione del legno, le norme standard esistenti riguardano test di efficacia e durabilità del legno nei confronti di diversi organismi, come i funghi lignivori, organismi marini perforanti (es. Teredini) e, tra gli insetti, i coleotteri xilofagi (Anobiidae, Lyctidae, Cerambycidae) e le termiti (Dictyoptera: Isoptera). Tuttavia, considerando in particolare le termiti, le uniche norme esistenti (UNI EN117, UNI EN118) riguardano esclusivamente le termiti sotterranee (Rhinotermitidae) come Reticulitermes spp. Le cosiddette termiti “del legno secco” (Kalotermitidae), rappresentate in Europa da Kalotermes flavicollis e Cryptotermes brevis, sempre più frequentemente si annoverano come pericolosi infestanti di manufatti lignei ed elementi strutturali per abitazioni/edifici. Queste termiti sono assai diverse da quelle sotterranee per caratteristiche biologiche ed etologiche, modalità di attacco e tipologia di danno sul legno e non è pertanto proponibile ne accettabile utilizzare le norme esistenti relative alle termiti sotterranee. Per sopperire all’assenza di norme internazionali ufficiali idonee, viene quindi proposto un protocollo specifico per verificare l’efficacia di trattamenti su legno contro specie di Kalotermitidi. Il presente lavoro era volto a testare l'efficacia di tre formulazioni di PAA (denominate A, B, C) come preservanti del legno, utilizzando per la termite sotterranea R. lucifugus lo standard EN 118, e per la termite del legno secco K. flavicollis il protocollo appositamente sviluppato. Dai risultati è emerso che tutte le formulazioni si sono rivelate efficaci come trattamenti preventivi nei confronti di R. lucifugus, facendo registrare un consumo di legno trascurabile ed una mortalità significativamente maggiore rispetto al controllo. Per quanto riguarda K. flavicollis, tutte le formulazioni di PAA hanno comportato una riduzione significativa del livello di attacco del legno e la formulazione B si è rivelata la più efficace anche nel ridurre la sopravvivenza delle termiti. Nel complesso, i trattamenti innovativi a base di PAA appaiono promettenti nella protezione del legno dagli attacchi delle termiti, risultando efficaci a basse concentrazioni, oltre ad avere un ridotto impatto ambientale e a dimostrare un buon fissaggio nel legno. Il protocollo proposto per la norma standard sulle termiti del legno secco si è rivelato valido ed efficace e potrebbe essere candidato tra le norme internazionali a questo scopo
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