Il legno archeologico imbibito in Cina e in Italia: comparazione delle metodologie diagnostiche e dei trattamenti, finalizzata allo sviluppo di nuovi protocolli comuni.

Progetto comune di ricerca

Responsabili di progetto: Nicola Macchioni, Dawa Shen
Accordo: CINA - CACH - Chinese Academy of Cultural Heritage
Bando: CNR/CACH 2016-2018
Dipartimento: Scienze bio-agroalimentari
Area tematica: Scienze bio-agroalimentari
Stato del progetto: Nuovo

Proposta di ricerca

Wet organic archaeological materials are always fragile. They are prone to be destroyed by physical, chemical, mechanical, and biological factors. During the archaeological excavation, wet organic archaeological materials are very hard to be managed.
Among the organic ones, wood is the most important archaeological material. Wood is one of the natural materials earliest utilized by human beings. From the prehistoric period all sorts of wooden objects, from small artefacts to magnificent architecture and shipwrecks, could be found.
China and Italy, due to their important and long history are characterised by fundamental archaeological findings and wood is increasing its importance due to recent excavations in which wooden artefacts were the principal findings. In Italy some important examples are the Roman ships in Pisa, the port of Olbia, several structures and artefacts in Herculaneum. In ancient China, wood was the most important construction material not only for the living but also for the dead. For example, in Han dynasty, (202 B.C.- 220 A.D.), the Mausoleum of the royal family was made with cypress, called "HuangchangTicou" (Walls Built of Cypress Heartwood). In 2010, the largest HuangchangTicou has been excavated in Shandong Province, China, and more than 2200 cubic meter of waterlogged wood was found. More recently some important shipwrecks including Nanhai, Huaguangjiao and Xiaobaijiao were excavated.
Waterlogged archaeological wood refers to wood that has been excavated by archaeologist-regardless of size, species, age, or state of preservation- and is completely filled with water. During burial, cellulose and hemicelluloses in wood cell wall are partially degraded by bacteria and fungi. Due to degradation, cell walls become more porous, causing an increase in water adsorption. In most degraded cases, the cell wall is too fragile to stand the stress, and collapse eventually.
Although there are some successful cases of air-dried waterlogged wood, consolidation is needed in most case due to the fragility of waterlogged wood artefacts. From early XX century, different consolidation methods have been developed to preserve all kinds of waterlogged archaeological wooden objects.
Alum maybe is the first chemical being used as consolidant for the conservation of waterlogged wood. In the early 1900's, alum was widely used in Scandinavia, and then worldwide. But nowadays, conservators recognize that alum could induce lethal destroy to wooden artefacts, and some groups are trying to find the way to extract it from the artefacts.
Poly ethylene glycol (PEG) was abundantly used in the conservation of world famous Sweden war ship Vasa, and since then it became the most widely used consolidation material for waterlogged wood. PEG with different molecular weight including 400, 600, 1000, 1500, 2000, 4000 could be used in the wood with different degradation degrees.
As a replacement of PEG, the analogue of PEG, Poly alcohol is also used universally in Asia. Acetyl alcohol and stearyl alcohol are common polyalcohol used in China.
Sugar and sugar alcohol are also used as consolidant. Sucrose is the first saccharide compound used in waterlogged wood conservation. After 1980's, more and more attention has been paid to the application of saccharides. Trehalose and sucralose were tested as conservation alternatives to sucrose due to their long-term stability and resistance to hydrolysis. In addition, sugar alcohol such as lactitol was used as consolidant too.
Melamine-Formaldehyde resins are also used in consolidation of waterlogged wood. From 1998 Kauramin method was used in consolidation of waterlogged wood in Germany. Good penetration of MF resin in the wood leads to good stabilization of the wood. According to the similar principle, Glyoxal is used in the consolidation of waterlogged wood in China especially for the conservation of the wooden body of Chinese lacquer ware.
Except for the chemical consolidation methods, consolidant combining the physical drying methods, such as freeze drying, and supercritical fluid were also used in the drying of waterlogged wood.
The selection of consolidation method differs from the specific condition of the wood. An object to be consolidated must be characterized firstly to identify the wood species and determine the type and extent of deterioration. Some physical and mechanical parameters are important, such as water content, density and shrinkage. The microstructure could be observed directly through optical microscope, SEM and TEM, to determine wood species and degradation level. Chemical analyses determine the residual chemical composition of degraded wood measuring the amounts of cellulose, hemicelluloses, and lignin. Generally, wood is a natural polymeric material and all instrumental analysis methods used in characterization of polymers are effective in the characterization of wood. FT-IR, Py-GC/MS, NMR spectroscopy and GPC could be used to characterize the composition and degradation of wood qualitatively but also quantitatively. XRD could be used to characterize the degradation measuring the crystallinity of the residual cellulose. Proper description of the wood condition is crucial to design the consolidation method; e.g. an archaeological wooden object in very good conditions could also suggest avoiding any consolidation treatment.
CACH in China and CNR-IVALSA in Italy have a large experience and international collaborations on the above topics. Through meetings and exchanges during a triennial activity they want to shear their experience on each one of the topic: diagnosis, conservation/consolidation and the design of the proper consolidation from the results of the diagnosis.

Obiettivi della ricerca

The general situation of archaeological waterlogged wood conservation in Italy and China will be reviewed. The object typologies, the most common wood species, the decay levels of waterlogged wood in the two countries will be compared. The technical standards related to waterlogged wood conservation will be compared.
In addition, the diagnosis methods used in Italy and China will be summarized. The diagnosis methods will be categorized into anatomical observation, physical measurements and chemical characterisation. The sampling method, measured parameters, instrumental analysis procedure and data processing method will be compared. Pros and cons of these methods will be commented.
The principal consolidation methods nowadays used in Europe and Asia will be summarized and compared. The connection of consolidation methods selection with wood species and degradation degree will be summarized. And the suitability, application scope and effectiveness of different consolidation methods will be commented. The development of waterlogged wood consolidation methods in the future will be suggested.
Based on this research, experiences exchange will be developed among China and Italy in order to develop a common protocol on waterlogged wood conservation. New characterization and consolidation methods can be introduced and a common pave for future collaborations and developments could be built.

Ultimo aggiornamento: 06/05/2025