Lo studio del legno archeologico mediante tecniche cromatografiche e spettrometria di massa: il caso del sito di Ercolano

La valutazione dello stato di degrado del legno, soprattutto quello archeologico, è una problematica di grande importanza in quanto il legno è sempre stato un materiale di vitale interesse per l’uomo sin dall’antichità ed è stato utilizzato per ogni tipo di necessità. Nonostante questo, oggetti lignei sono piuttosto rari da trovare nei musei, in quanto il legno può essere facilmente degradato da funghi, batteri e insetti e la sua conservazione dipende in modo drastico dalle condizioni di giacitura dell’oggetto nel corso dei secoli: ambienti poveri di ossigeno, in cui l’attività di funghi e microrganismi è ridotta, permettono la sopravvivenza del legno per lunghi periodi. Tuttavia, una volta estratto dall’ambiente di giacitura, il legno presenta un’altra serie di problematiche legate al cambiamento delle condizioni esterne e in particolare alla sua igroscopicità, che possono causare alterazioni della struttura tali da compromettere la fruibilità dell’oggetto stesso. Il legno bagnato e il legno carbonizzato hanno caratteristiche particolari in termini di conservazione: nel primo caso l’ambiente acquatico previene l’attacco di molte specie di funghi e batteri, ma batteri anaerobi e particolari specie di funghi riescono ad attaccare soprattutto la componente polisaccaridica del legno, lasciando un materiale poroso e spugnoso, le cui cavità sono riempite di acqua; nel secondo caso la carbonizzazione (combustione in assenza di ossigeno) provoca la perdita della maggior parte delle componenti del legno, lasciando un residuo essenzialmente ligninico e molto fragile. In entrambi i casi, tuttavia, la forma dell’oggetto è conservata: trattamenti protettivi e consolidanti diventano di fondamentale importanza al fine di conservare il materiale ligneo nelle migliori condizioni e garantire la sopravvivenza dell’oggetto una volta estratto dal luogo di giacitura. Il primo passo per decidere i trattamenti da applicare su oggetti lignei è comunque la valutazione dello stato di degrado del materiale attraverso tecniche analitiche di tipo fisico e chimico, in quanto non esiste un protocollo di intervento sulla base del quale prendere decisioni a priori: ogni caso deve essere valutato singolarmente. Lo scopo di questo lavoro di tesi è quello di valutare lo stato di degrado del legno prelevato da alcuni reperti ritrovati nel sito archeologico di Ercolano e di individuare la tecnica pittorica usata per quei campioni che conservano ancora una parte dello strato pittorico originale. Il lavoro si inserisce all’interno dell’Herculaneum Conservation Project, un progetto internazionale il cui scopo è quello di sostenere lo stato italiano nella salvaguardia del fragile sito di Ercolano, avvalendosi di strumenti scientifici per ottenere informazioni affidabili e utilizzabili al fine di pianificare un intervento di conservazione il più accurato possibile. La letteratura sulla caratterizzazione chimica del legno degradato si concentra soprattutto sul legno non archeologico, ma il legno fresco e il legno archeologico hanno lo stesso “destino chimico” a lungo termine nell’ambiente, perciò possono essere caratterizzati tramite le stesse tecniche analitiche. Gli studi effettuati sul legno archeologico, inoltre, riguardano soprattutto campioni di legno bagnato o imbibito d’acqua, mentre la letteratura sul legno carbonizzato è piuttosto scarsa. La caratterizzazione del legno è basata su metodi classici di trattamento a umido, che richiedono grandi quantità di campione e di reagenti e un tempo di analisi molto lungo, caratteristiche che rendono questi metodi non adatti all’applicazione nel campo dei beni culturali. Altre tecniche sono state applicate allo studio del legno (NMR, FT-IR, TGA, DSC, XRD ed altre), ma nessuna di queste fornisce risultati quantitativi né risulta utile all’analisi di campioni archeologici, in cui la quantità di campione è spesso molto bassa. In questo lavoro la tecnica di Py(HMDS)-GC/MS è stata scelta ed utilizzata per la valutazione dello stato di degrado del legno, in quanto questa tecnica non richiede pretrattamento del campione, utilizza una quantità di campione dell’ordine di 0.1 mg, è veloce e sensibile e permette di ottenere informazioni a livello molecolare utili all’individuazione dei prodotti di degradazione del legno e a un’analisi di tipo semiquantitativo delle sue componenti. Dal punto di vista chimico, infatti, il legno può essere visto come una miscela complessa dei biopolimeri cellulosa, emicellulose e lignina, perciò la pirolisi analitica è particolarmente indicata, in quanto permette lo studio di macromolecole complesse attraverso l’osservazione di molecole di piccole dimensioni (prodotti di pirolisi), che contengono molte informazioni sui polimeri di partenza. Le condizioni strumentali sono state ottimizzate a partire da quelle utilizzate in letteratura al fine di ricavare un metodo analitico capace di fornire un maggior numero di informazioni rispetto a quelle ottenute con i metodi classici e in un tempo minore. Per quanto riguarda i campioni di legno dipinto, l’identificazione della tecnica pittorica è stata effettuata tramite analisi GC/MS, seguendo una procedura riportata in letteratura, che permette l’analisi di tutti i materiali organici usati in pittura a partire da un unico micro-campione

Timing in Analytical Pyrolysis: Py(HMDS)-GC/MS of Glucose and Cellulose Using Online Micro Reaction Sampler

A novel analytical approach based on pyrolysis-gas chromatography coupled with mass spectrometry of carbohydrates with in situ silylation using hexamethyldisilazane is presented in this work for the first time. A micro reaction sampler was used to simultaneously achieve the pyrolyis reaction and facilitate the derivatization of pyrolysis products, by enabling the materials to react with the derivatizing agent in a sealed capsule at high temperature and pressure for long periods of time. This drastically increased the complete silylation of the pyrolysis products and the chromatographic resolution, resulting in less complex pyrograms and increased sensitivity toward the most stable compounds. Different results were obtained for glucose and cellulose in terms of predominant pyrolytic pathways. The formation of anhydrosugars was the preferential pyrolytic reaction for glucose, while the formation of cyclopentenones and small molecules was predominant for the pyrolysis of cellulose. Steric hindrance effects of polysaccharide chains on the efficiency of the derivatizing agent were hypothesized in order to explain the different results. A good reproducibility was found, with relative standard deviations not greater than 10%. Semiquantitative calculations showed that the partial silylation of anhydrosugars was almost completely overcome after 10 min of reactive pyrolysis. This work discloses a powerful and potentially widely applicable analytical method for the investigations of organic materials under controlled pyrolytic conditions, with the advantage of increasing the effectiveness of in situ derivatization

New markers of natural and anthropogenic chemical alteration of archaeological lignin revealed by in situ pyrolysis/silylation-gas chromatography-mass spectrometry

Analytical pyrolysis coupled with gas chromatography and mass spectrometry with in situ silylation using hexamethyldisilazane (Py(HMDS)-GC/MS) was used to investigate the chemical alteration patterns of a set of archaeological waterlogged oak and silver fir woods. The samples were collected from five piles removed from stilt houses found in a Neolithic village (Bracciano lake, Rome, Italy) and from various parts of the roof of a Roman house (Herculaneum, Italy).We discuss on how the molecular information provided by Py(HMDS)-GC/MS revealed the causes and effects of natural and anthropogenic alteration and degradation of lignin, and how the adoption of silylation reactions lead to the detection of very informative pyrolysis products. Very particular pyrolytic patterns were obtained for the archaeological samples investigated, which were mainly characterised by the presence of oxidised compounds such as vanillin, acetovanillone, vanillic acid, syringaldehyde, acetosyringone, and syringic acid.We also report the first ever identification of the methyl esters of vanillic and syringic acids in their silylated form using this method. The results are consistent with heating processes undergone by archaeological wood due to natural or anthropogenic causes: the wooden roof from Herculaneum was naturally exposed to high temperatures during the eruption of Vesuvius, and the wood piles may have been artificially heated by people in the Neolithic Age to enhance the waterproof properties of wood.Due to the importance of identifying lignin pyrolysis products, the identification and mass spectra of sixty lignin pyrolysis products in their silylated form are also presented

Analytical Instrumental Techniques to Study Archaeological Wood Degradation

Historically, a very large variety of everyday artifacts were made of wood, which makes them representative of their historical period or social context and valuable for archaeologists and historians. In order to preserve degraded wood and to develop and apply suitable conservation treatments, chemical and physical characterization of archaeological wood is needed. This review provides the reader with a survey on state-of-the-art of instrumental analytical tools available to understand the morphology and the chemical composition of archaeological wood. The focus is on microscopic and spectroscopic techniques such as scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Raman, nuclear magnetic resonance (NMR) and analytical techniques based on pyrolysis, such as direct exposure-mass spectrometry (DE-MS), pyrolysis-mass spectrometry (Py-MS), pyrolysis-gas chromtography-mass spectrometry (Py-GC/MS), with emphasis on their respective potentialities and limitations. The advantages of techniques based on synchrotron radiation are also discussed. In addition, the applicability of each examined technique is illustrated and discussed through specific examples from the literature

Analytical Pyrolysis and Mass Spectrometry to Characterise Lignin in Archaeological Wood

This review describes the capability of analytical pyrolysis-based techniques to provide data on lignin composition and on the chemical alteration undergone by lignin in archaeological wooden objects. Applications of Direct Exposure Mass Spectrometry (DE-MS), Evolved Gas Analysis Mass Spectrometry (EGA-MS), and single and double-shot Pyrolysis-Gas Chromatography/Mass Spectrometry (Py-GC/MS) in archaeological lignin characterisation are described. With comparison to cellulose and hemicelluloses, lignin is generally less prone to most degradation processes affecting archaeological artefacts in burial environments, especially waterlogged ones, which are the most favourable for wood preservation. Nevertheless, lignin also undergoes significant chemical changes. As wood from waterlogged environments is mainly composed of lignin, knowledge of its chemical structure and degradation pathways is fundamental for choosing preventive conservation conditions and for optimising consolidation methods and materials, which directly interact with the residual lignin. Analytical pyrolysis coupled with mass spectrometry, used in several complementary operational modes, can gather information regarding the chemical modifications and the state of preservation of lignin, especially concerning oxidation and depolymerisation phenomena. Several applications to the analysis of wood from archaeological artefacts affected by different conservation problems are presented to showcase the potential of analytical pyrolysis in various scenarios that can be encountered when investigating archaeological waterlogged wood

Oak wood degradation processes induced by the burial environment in the archaeological site of Biskupin (Poland)

The open-air Archaeological Museum in Biskupin (Poland) preserves and shows to the public a prehistoric settlement of Lusatian culture dating back to Early Iron Age (eighth century BC). The monitoring of the environment and dynamics of the wood degradation in the burial conditions at the site is fundamental for the in situ preservation of archaeological wooden materials. A monitoring program thus started in 2003 at the Biskupin site, using contemporary sound oak wood that was placed in two wet burial environments, characterised by different conditions. A multi-analytical protocol was exploited to obtain information on the structural, physical and chemical conditions of the buried wood. The study involved the application of gravimetric and wet chemical analysis, and instrumental techniques, including infrared spectroscopy (FTIR) and analytical pyrolysis (Py–GC/MS) to evaluate alterations in the buried oak wood over a 10-year period. The results showed that, during the burial period in both monitoring stations, there was only limited chemical transformation of the polysaccharide component, mostly involving hemicelluloses. The differences observed might be due to the natural compositional variability and inhomogeneity of oak wood. The final condition of the wood was very similar in the two burial environments. It is therefore suggested that the wet burial conditions in the Biskupin site represent a safe conservation environment for the in situ preservation of the wood remains, at least those presenting a good initial preservation state. This supports the conservation strategy adopted in the Biskupin Museum site

An investigation into the curing of urushi and tung oil films by thermoanalytical and mass spectrometric techniques

Urushi is the oldest and most precious lacquer used since antiquity in East Asia. For artistic purposes, in order to obtain suitable rheological properties, the lacquer is usually mixed with a vegetable oil. In this work we investigated the curing process of urushi/tung oil mixtures in order to highlight the chemical interactions at the molecular level between the two materials. A multi-analytical approach was adopted, based on thermogravimetry (TG), differential scanning calorimetry (DSC), gas chromatography-mass spectrometry (GC-MS), evolved gas analysis mass spectrometry (EGA-MS), analytical pyrolysis coupled with gas chromatography and mass spectrometry (Py-GC-MS) and high performance liquid chromatography-mass spectrometry (HPLC-MS). Fresh and aged mixtures were analysed and the results were compared with those obtained from the analysis of the individual materials. The data highlighted that different polymerization and oxidation mechanisms take place in oil/urushi mixtures compared to the pure materials. Py-GC-MS and GC-MS showed that the profile of aliphatic mono- and di-carboxylic acids was drastically different for the aged film of pure tung oil compared to the mixtures. The ratio between the relative content of azelaic and palmitic acids was much lower in the mixtures than in the pure oil, highlighting a lower level of oxidation. On the other hand, the relative content of short chain carboxylic acids, which are produced by pyrolysis of the cross-linked oil network, increased as the concentration of urushi in the mixtures increased, thus indicating an increasing level of reticulation. HPLC-MS showed a relatively higher amount of triglycerides with hydroxylated fatty acids – the intermediate oxidation product of polyunsaturated fatty acids - in the mixtures with respect to pure tung oil

Dinámica lateral de una dupla ferroviaria articulada

Las duplas ferroviarias articuladas son vehículos modulares conformados por dos coches y una unidad motriz (UM) situada entre ellos. Cada coche exhibe la particularidad de poseer sólo un bogie en un extremo y estar apoyado sobre la UM. Estos tipos de vehículos presentan condiciones particulares de inestabilidad debido a la naturaleza propia de la configuración utilizada. Todo fenómeno producido en la dinámica del sistema es magnificado por la complejidad de la distribución de la formación analizada. El módulo de propulsión (UM) constituye el componente con mayor influencia sobre la dinámica de los coches conducidos, generando así, el interés de su estudio. El objetivo general es identificar la gama de parámetros de prueba necesarios para la evaluación del rendimiento del vehículo y determinar las condiciones críticas que limitan la velocidad longitudinal de desplazamiento, lo cual produce la reducción del confort de marcha y afectan la seguridad frente al descarrilamiento. Una limitación importante en el transporte ferroviario es el producido por las vibraciones laterales como respuesta al contacto con la vía. Dichas vibraciones en los coches de pasajeros reducen el confort de marcha, y son capaces de generar un severo desgaste tanto de los rieles como en las ruedas del bogie. Bajo condiciones extremas, estas oscilaciones pueden dar lugar al descarrilamiento de la formación. Existen dos conceptos básicos a considerar en el comportamiento dinámico lateral de vehículos ferroviarios: es el fenómeno conocido como hunting, y la velocidad crítica. El primero de ellos, refiere a la utilización de una sección cónica variable en los perfiles de ruedas, es un movimiento armónico, periódico y oscilante. El segundo, es la velocidad crítica, la cual puede definirse como la velocidad a partir de la cual el vehículo presenta un cambio considerable en su comportamiento dinámico. A bajas velocidades (< 30 km/h), el fenómeno se observa como una oscilación del coche, de gran amplitud, baja frecuencia, a velocidades más elevadas (> 70 km/h), aumenta la probabilidad de producirse una oscilación de aparición violenta, alta frecuencia, generando el peligro de un eventual descarrilamiento. En el presente estudio, se ha realizado el análisis dinámico de la dupla articulada denominada “Alerce”, de la empresa EMEPA. Dicha dupla se encuentra actualmente en funcionamiento como transporte de pasajeros en la línea Belgrano Norte, en el área metropolitana

A multi-scalar investigation of the colouring materials used in textile wrappings of Egyptian votive animal mummies

Commonly exhibited in museum galleries, animal mummies have been the focus of interest of both visitors and researchers alike. The study of these animal remains not only provides new insights into embalming techniques, but also brings a unique perspective on religious, social and economic practices. Twenty animal mummies are discussed in this study, including cats, ibises, crocodiles, calves and birds of prey from the collections of the British Museum (London, UK) and the Museo Egizio (Turin, Italy). The external textile wrappings encasing the mummified body of the animals were investigated with the main aim of identifying the colourants used. In fact, these are mostly patterned using undyed and coloured (mostly red, brown and black) linen strips. Broadband multispectral imaging (MSI) was initially carried out to obtain preliminary information at the macro-scale on the distribution and chemical nature of the colouring agents. Fibre optic reflectance spectroscopy (FORS) was then used to survey several coloured areas of the textile wrappings. Safflower (Carthamus tinctorius) and red ochre were identified non-invasively. Representative samples were then taken and observed using optical microscopy (OM) and scanning electron microscopy (SEM), in order to obtain information at the micro-scale on the distribution of the colouring agents on the fibres, as well as the presence of other materials, including those from environmental contamination. Energy dispersive X-ray spectrometry (EDX) revealed the elemental composition of particles and clear areas of the fibres, whereas high performance liquid chromatography tandem mass spectrometry (HPLC\u2013MS/MS) provided the identification of the organic dyes at a molecular level. The use of hydrolysable and condensed tannins, in combination with iron as a mordant, was found to be used in the very dark shades, which generally corresponded to the textiles with the worst state of preservation. Nevertheless, other aspects, such as fibre processing and bleaching, fungal attack and presence of coating materials appeared to play a role in the evaluation of the conservation state of these textiles. The characterisation of the dyes and the additional inorganic materials contributed to elucidating the production technology of the colours used for animal mummification, and provided insights into ancient dyeing methods