Progetto comune di ricerca

Il legno archeologico bagnato: un approccio multi-analitico per diagnosticare il degrado

Responsabili di progetto
Mariaperla Colombini, Boguslaw Gediga
Accordo
POLONIA - PAN (NUOVO ACCORDO) - Polish Academy of Sciences/Polska Akademia Nauk
Bando
CNR-PAN 2017-2019
Dipartimento
Scienze umane e sociali, patrimonio culturale
Area tematica
Scienze umane e sociali, patrimonio culturale
Stato del progetto
Nuovo

Proposta di ricerca

The project aims to involve Polish and Italian research institutions in a program that will adopt a multi analytical approach to investigate the chemical composition of wet wooden materials in archaeological artifacts and to evaluate their preservation state.
Wet wood is defined as a porous, spongy material, found in aquatic or humid environments, with extremely high water content (100-2000%). The prolonged permanence in an aqueous environment usually causes an extensive loss of cellulose and hemicelluloses, as well as partial degradation and alteration of the lignin, in addition to the loss of soluble extractives. Drastic dimensional changes, structural distortions and cracking may occur during drying of wet wood artifacts. Consequently, conservation treatments of wet archaeological wooden objects are generally aimed at preventing these phenomena, and in many cases, they involve the replacement of water by filling the microcavities of the wooden structure with compatible materials.
The investigations of the chemical alterations occurred in wet archaeological and historical wooden objects allows us not only to study the degradation pathways of lignocellulosic materials, but also to develop appropriate consolidation methods and/or conservation treatments.
Many different analytical techniques have been developed and employed to measure the extent of wood deterioration. The classical gravimetric methods of wood analysis, developed in the field of pulp and paper industry, can be used to determinate the amount of wood components after their isolation and purification. Analytical thermal degradation techniques (EGA-MS, Py-GC/MS) can be used for characterization of holocellulose and lignin in archeological wood. Furthermore, techniques based on X-rays such as SEM-EDS, XRD or XRF are commonly used for the assessment of the inorganic components present in archaeological waterlogged wood rich in salts and sediments, which are often unstable and interact with wood inducing specific deterioration pathways.
Within the proposed project an analytical protocol will be developed and applied by using different analytical techniques to study wet archaeological wood, in order to obtain complementary results. This will be possible by exploiting the skills and equipment present in the laboratories of Italian and Polish partners.
The methods adopted by the Polish partner will be based on classical wet techniques for the characterization of the main components of wood, and on spectroscopic techniques (FT-IR) The Italian laboratories will conduct an analytical study applying thermal degradation techniques as evolved gas analysis (EGA-MS) and analytical pyrolysis coupled to gas chromatography and mass spectrometry (Py-GC/MS) in order to characterize more in detail lignin, cellulose and hemicelluloses, and also to better understand the alterations which affect each lignocellulosic polymer during burial environment.
The gain of knowledge about the inorganic components present in the wooden structure also proved fundamental for the preservation of archaeological wooden objects. Inorganic species derive from burial environments , and their instability can contribute to induce degradation processes of the wood during conservation and after the application of the consolidation treatments. The Italian partner will apply X-rays based techniques, such as SEM-EDS and XRF, for the assessment of elemental composition, and XRD for the assessment of the composition of crystalline compounds. Morphological investigation and elemental mapping will be also provided by SEM-EDS.
In addition, the evanescent field dielectrometry system in resonant configuration (called SUSI) will be tested during the project for its potential applications to wet archaeological wood. This system is used at present to diagnose the sub-surface presence of moisture content and salts within plaster, mortar, stone and particularly in frescoes, but a properly calibration could be used to detect the water level inside wood.
Furthermore, since the analytical techniques employed for carrying out the project allow to collect large data set relating to a high number of samples and analytes, multivariate statistical techniques will be applied to interpret the results (pattern analysis, principal component analysis). This will allow to compare samples in a quantitative way, in order to integrate the information from the same sample studied by more than one analytical technique.
During the project analytical methods will be optimized, verified and compared by the Polish and Italian research groups, with a focus in assessing the potentiality in the study of archaeological wood-based materials. The second main result will be to obtain reliable data related to the characterization of archaeological waterlogged wooden objects studied in the project. The results obtained during the project will be included in scientific publications and catalogs describing the sites and investigated objects, and used to implement the display of the investigated objects in museum In fact the results will hopefully allow to better contextualize the objects in the society that produced it, assessing their technological skills of , in addition to determine the state of preservation.
The Italian and Polish partners have been working together since several years studying the degradation of archaeological wood. The collaboration has led to many publications in scientific journals and several communications at national and international conferences. In addition, as part of the COST IE0601 wood for the Conservation of Cultural Heritage, one of the members of the Italian research group carried out a research period of one week in the Polish laboratory. This cooperation has allowed reciprocal understanding of the scientific competence of both Polish and Italian parties.

Obiettivi della ricerca

o to achieve the exchange of scientific knowledge between the Polish and Italian research groups. Since several years both groups work in chemistry applied to wet wooden materials, particularly for conservation purposes. The Polish group is specialized in the study of the composition of wood by classical wet methodologies, whereas the Italians in studying wood by instrumental techniques.
o to develop and evaluate a multi-analytical approach able to obtain information on the state of preservation of wet archaeological wood, by microscopic techniques (MO,SEM-EDX), spectroscopic measurements (FT-IR, XRD, XRF) and by thermal and chromatographic techniques (EGA-MS, Py-GC/MS). The SUSI system will inform on the water and salt contents in situ. The final diagnosis comes from connecting up the various analytical results, also with the aid of statistical analysis, making it possible to correctly evaluate the actual state of preservation of the archaeological material. The chemical study of degradation processes will contribute not only to understand the biodegradation of wood structure, but also to the development of appropriate conservation treatments.
o to a better understanding of degradation processes occurring in wet archaeological wood; elucidation of the mechanisms and the causes of the deterioration processes taking place in degraded wood. The knowledge transfer will involve also graduate and undergraduate students participating to the project.

Ultimo aggiornamento: 28/03/2024