Advances in Understanding Microbial Deterioration of Buried and Waterlogged Archaeological Woods: A Review

Characterization of Culturable Mycobiome of Newly Excavated Ancient Wooden Vessels from the Archeological Site of Viminacium, Serbia

Two ancient wooden vessels, specifically a monoxyle (1st century BCE to 1st century CE) and shipwreck (15th to 17th century CE), were excavated in a well-preserved state east of the confluence of the old Mlava and the Danube rivers (Serbia). The vessels were found in the ground that used to be river sediment and were temporarily stored within the semi-underground exhibition space of Mammoth Park. As part of the pre-conservation investigations, the primary aim of the research presented was to characterize the culturable mycobiomes of two excavated wooden artifacts so that appropriate conservation procedures for alleviating post-excavation fungal infestation could be formulated. Utilizing culture-based methods, a total of 32 fungi from 15 genera were identified, mainly Ascomycota and to a lesser extent Mucoromycota sensu stricto. Soft-rot Ascomycota of genus Penicillium, followed by Aspergillus and Cephalotrichum species, were the most diverse of the isolated fungi. Out of a total of 38 isolates, screened on 7 biodegradation plate assays, 32 (84.21%) demonstrated at least one degradative property. Penicillium solitum had the highest deterioration potential, with a positive reaction in 5 separate plate assays. The obtained results further broaden the limited knowledge on the peculiarities of post-excavation soft-rot decay of archaeological wood and indicate the biochemical mechanisms at the root of post-excavation fungal deterioration.

A multi-technique and multiscale comparative study on the efficiency of conservation methods for the stabilisation of waterlogged archaeological pine

Archaeological wood can be preserved in waterlogged conditions. Due to their degradation in the ground, these archaeological remains are endangered after their discovery, since they decay irretrievably during drying. Conservation measures are used to preserve waterlogged archaeological objects, maintaining their shape and character as much as possible. However, different methods have been developed leading to varying results. This study compares their effectiveness in order to clarify their mode of action. The methods including alcohol-ether resin, lactitol/trehalose, melamine formaldehyde, polyethylene glycol impregnation prior to freeze-drying, saccharose and silicone oil were assessed by analysing mass changes and volume stability using structured-light 3D scanning. The state of the conserved wood samples including the spatial distribution of the conservation agent was examined using synchrotron micro-computed tomography. Raman spectroscopy was used to observe the agent´s spatial distribution within the cells. The findings demonstrated that melamine formaldehyde stabilises the degraded cell walls. The lumens are void, as in the case with alcohol-ether resin, while polyethylene glycol, silicone oil, saccharose and lactitol/trehalose also occupy the lumens. It is assumed that the drying method has an effect on the distribution of the solidifying agent. The knowledge gained affords insights into the mechanism of conservation methods, which in turn accounts for the varied outcomes. It also allows conclusions to be drawn about the condition and stability of conserved museum objects and serves as a starting point for the further development of conservation methods.

New frontiers review of some recent conservation techniques of organic and inorganic archaeological artefacts against microbial deterioration

The information on the advances and technology of some recent conservation methods (2020–2023) of organic and inorganic archaeological objects against microbial deterioration is recorded. An outline of comparative new protective methods for conserving plant-origin organic artefacts {Fibers (manuscripts, textile) and wood}, animal-origin organic artefacts (painting, parchment and mummies) and inorganic stone artefacts were investigated. The work not only contributes to the development of safe revolutionary ways for more efficient safe conservation of items of historical and cultural worth but also serves as a significant diagnostic signature for detecting the sorts of microbial identification and incidents in antiques. Biological technologies (environmentally friendly green biocides) are the most used recent, efficient and safe strategy acceptable as alternatives to stop microbial deterioration and prevent any potential interactions between the biological agent and the artefacts. Also, a synergistic effect of combining natural biocides with mechanical cleaning or chemical treatments was suggested. The recommended exploration techniques should be considered for future applications.

Non-destructive preservation state estimation of waterlogged archaeological wooden artifacts

Non-destructive preservation state estimation is an essential prerequisite for the preservation and conservation of waterlogged archaeological wooden artifacts. Herein, Near Infrared (NIR) spectroscopy coupled with orthogonal partial least squares discriminant analysis (OPLS-DA) were applied to assess sixty-four waterlogged archaeological woods collected from seven excavation sites in the period range of 2900 BCE-1912 CE, aiming at developing a non-destructive, accurate and rapid preservation state estimation methodology. The role of non-decayed recent wood of relevant species on preservation state estimation was studied in prior, showing the use of non-decayed recent wood could not improve the predictive ability. Besides, the high variability in terms of chemical structure between archaeological softwoods and archaeological hardwoods did affect the preservation state estimation. Thus, a simple OPLS-DA model of non-destructively distinguishing archaeological hardwoods from softwoods, R²X_cum of 0.659, R²Y_cum of 0.836 and Q²_cum of 0.763, was established to avoid and overcome destructive approach for wood identification. Then, the well-defined three grouped separations of slightly-decayed, moderately-decayed and severely-decayed waterlogged archaeological woods were revealed in OPLS-DA models, providing R²X_cum of 0.793, R²Y_cum of 0.738, Q²_cum of 0.680, and R²X_cum of 0.780, R²Y_cum of 0.901, Q²_cum of 0.870, for waterlogged archaeological hardwoods and waterlogged archaeological softwoods respectively. Potential predictive wood spectral bands were screened and tentatively identified as hydroxyls of crystalline cellulose, acetyl groups of hemicelluloses, C-H bands of lignin, which guaranteed the elimination of non-structural compounds, such as water and inorganic components interference. Furthermore, the developed NIR methodology was validated by an extensively used destructive method consisting of anatomical characteristics, maximum water content and basic density analyses. The results indicated that NIR coupled to chemometrics could non-destructively and accurately predict the preservation states of waterlogged archaeological wooden artifacts and avoid the interference of water and inorganic deposits.

Biodeterioration Assessment of a Unique Old Pharaonic Kingdom Wooden Statue Using Advanced Diagnostic Techniques

A recently discovered Egyptian wooden statue of King Djedefre was studied together with some surrounding burial soil samples for assessing the statue biodeterioration. The wooden morphological characterisation identified the hardwood Acacia nilotica as the wood type. X-ray diffraction, micro-FT-IR spectroscopy, and scanning electron microscopy with an X-ray spectrometer were used to evaluate the wood deterioration degree and the soil contribution in wood biodeterioration. Microbiological analyses (fluorescent in situ hybridisation and polymerase chain reaction) were also performed to detect the microbial attack on the statue. The prolonged interaction of the statue with the burial environment caused a strong wood decay due to biotic (fungi and bacteria) and abiotic factors (e.g., humidity fluctuations of the burial environment), which caused the severe cracking and collapsing of the wood structures. The analyses of the burial soil mineral composition were relevant for obtaining an overall picture of the statue deterioration. The results are useful for planning the right conservation procedures for this very particular and important wooden statue. Furthermore, analysis of the woody cell wall will help in the selection of appropriate consolidation and recovery treatments. Because the statue is a unique single piece of wood, and the morphological observations indicated that it is a bald woman in a sitting position, this statue will provide new and interesting knowledge of Egyptian culture.