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

A milk and ochre paint mixture used 49,000 years ago at Sibudu, South Africa

Gas chromatography/mass spectrometry, proteomic and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDS) analyses of residue on a stone flake from a 49,000 year-old layer of Sibudu (South Africa) indicate a mixture of ochre and casein from milk, likely obtained by killing a lactating wild bovid. Ochre powder production and use are documented in Middle Stone Age South African sites but until now there has been no evidence of the use of milk as a binder. Our analyses show that this ochre-based mixture was neither a hafting adhesive nor a residue left after treating animal skins, but a liquid mixture consisting of a powdered pigment mixed with milk; in other words, a paint medium that could have been applied to a surface or to human skin. The significance of our finds also lies in the fact that it establishes the antiquity of the use of milk as a binder well before the introduction of domestic cattle in South Africa in the first millennium AD

WET ARCHAEOLOGICAL WOOD: CHEMICAL STUDY OF DEGRADATION AND EVALUATION OF CONSOLIDATION TREATMENTS

The present work describes a thoroughly analytical study of the chemical changes produced in waterlogged woods collected from different different archaeological sites. This study is very important in order to develop appropriate measures for the conservation of historical wooden artifacts. The chemical changes produced in the waterlogged woods were studied by different pyrolytic techniques: direct exposure electron ionization-mass spectrometry (DE-MS), pyrolysis coupled with gas chromatography-mass spectrometry (Py-GC/MS) and Py-GC/MS in the presence of hexamethyldisilazane (HMDS) as a derivatising agent. The study concluded that the main structural changes occurring in waterlogged woods are the removal of carbohydrates. The lignin moiety remains largely unaltered, although some small changes could also be observed, such as depolymerisation, demethylation of methoxyl groups and some evidences of a slight oxidation of α-carbon of the lignin side-chain. In the last chapter, the author also describes the morphology of degraded archaeological waterlogged woods and the evolution of penetration of different wood impregnants by the use of X-ray synchrotron radiation microtomopraphy (SR-μCT), which gives useful insights into the use of different consolidation treatments

Characterisation of archaeological waterlogged wood from Herculaneum by pyrolysis and mass spectrometry

Chemical characterization is a valuable tool for assessing the decay of archaeological or historical degraded wood it and is essential in selecting the most appropriate conservation techniques. This paper reports the results on archaeological waterlogged wood remains from the roof of a Roman villa buried in AD 79 by the eruption of Vesuvius. Parts of the wooden roof were excavated in 2009 under several meters of solidified pyroclastic material in the area of the ancient shoreline, in an extremely wet environment. The sampling was undertaken in 2011 and samples were analyzed and characterized within the framework of the Herculaneum Conservation Project. The degradation of the wood was assessed by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), an analytical approach that achieves semi-quantitative results on the content of lignin and polysaccharides in degraded wood. The characterization was based on a comparison of the pyrolysis profiles of archaeological wood with sound wood of the same species. To compare samples according to their state of degradation, a multivariate statistical approach based on principal component analysis (PCA) was used. The analyzed samples revealed different levels of lignin oxidation, and different amounts of residual polysaccharide components, even between samples taken from the same fragment of the roof. This means that the wood underwent different degradation pathways, such as degradation by fungi or insects

The unprecedented identification of Safflower dyestuff in a 16th century tapestry through the application of a new optimized diagnostic procedure

A set of samples collected from two 16th century silk tapestries belonging to Quirinale Palace in Rome and presently under restoration at the Opificio delle Pietre Dure (Florence, Italy) was investigated in order to disclose the nature of the dyes employed in their production. The identification of the colouring materials was achieved through the application of an optimised reliable procedure, based on dimethylsulfoxide extraction of the dyes from the yarns followed by a hydrolysis treatment in an acidic methanolic solution with hydrochloric acid; the extract is then analysed by high performance liquid chromatography with diode array detector (DAD). This study has lead to the identification of a wide range of colours; expensive dyes were used to dye the analysed silk yarns: coccid dyestuffs, madder, weld, young fustic, tannins and an indigoid dye were identified. Moreover, the use of safflower has been assessed for the first time in a European fabric. (C) 2011 Elsevier Masson SAS. All rights reserved

A unique early medieval pendant (kaptorga) from Opole Groszowice (Silesia, SW Poland) in the light of interdisciplinary archaeometric studies

Finds of early medieval pendants, known as kaptorgas, are not common in Poland. For this reason, the kaptorga found in 1957 in Opole (Silesia), in southwest Poland, is all the more interesting. The artefact is housed in a museum, and on the occasion of its re-conservation, permission to conduct archaeometric studies was given. The kaptorga was subjected to analyses using nondestructive and minimally invasive techniques. Elemental tests with energy dispersive XRF and SEM-EDS spectrometers showed that the pendant is made of brass, not bronze sheet, as was originally thought. In its filling, there is a small fragment of plant-fiber thread (subjected to microscopic observations) and beeswax, which was identified using infrared spectroscopy and gas chromatography with a mass spectrometer