Session 6: Non-invasive techniques for the study of wooden cultural heritage


Tailoring X-ray imaging techniques for dendrochronology of large wooden objects

Francien G. Bossema1, 2, Marta Domínguez-Delmás2, 3, Willem Jan Palenstijn1, Alexander Kostenko1, Jan Dorscheid2, Sophia Bethany Coban1, Erma Hermens2, 3, K. Joost Batenburg1, 4

1Computational Imaging, Centrum Wiskunde & Informatica, Amsterdam, the Netherlands. 2 Conservation and Science department, Rijksmuseum, Amsterdam, the Netherlands. 3 Institute of Art History, Faculty of Humanities, University of Amsterdam, Amsterdam, the Netherlands. 4 Leiden Institute of Advanced Computer Science, Leiden University, Leiden, the Netherlands.

Tree rings are not always accessible on the outside of objects and thus X-ray computed tomography (CT) has been applied to visualise the tree rings in a non-invasive way for dendrochronological purposes. For large objects such as chests or cabinets, it is often impossible or impractical to rotate fully within the scanner as is necessary for CT. As a solution to this challenge, we developed a line trajectory X-ray tomography technique, in which the object is moved only sideways. This method, although not yielding a full 3D image, is particularly well suited to reveal tree rings. Using this easily implementable scanning trajectory, sharp reconstruction images of the tree rings can be obtained and used for dendrochronological measurements. This result is of importance to the fields of both imaging and dendrochronology and opens up a wide variety of objects of which the internal tree ring pattern can now be investigated using X-ray imaging.


Old and new, large and small: Non-invasive techniques applied to a musical instrument

Tamar Hestrin-Grader1, 2, 3, Manu Frederickx1, 4, 5, Marta Domínguez-Delmás2, 6, 7, Wolfgang Gard8, Ellen Meijvogel-de Koning9, Jan Willem van de Kuilen8, Francien Bossema10, Tristan van Leeuwen10, Paul van Duin2, Jan Dorscheid2, Tirza Mol2, Giovanni Paolo di Stefano11

1KASK & Conservatorium (HOGENT-Howest), Ghent, Belgium. 2 Department of Conservation & Science, Rijksmuseum, Amsterdam, the Netherlands. 3 Academy of Creative and Performing Arts, Universiteit Leiden, the Netherlands. 4 Objects Conservation, Metropolitan Museum of Art, New York, USA. 5 Department of Art, Music and Theatre Sciences, Faculty of Arts and Philosophy, University Ghent, Belgium. 6 Amsterdam School for Heritage, Memory and Material Culture, Faculty of Humanities, University of Amsterdam, Amsterdam, the Netherlands. 7 DendroResearch, Wageningen, the Netherlands. 8 Biobased Structures and Materials, Faculty of Civil Engineering and Geosciences, TU Delft, the Netherlands. 9 Laboratory of Geoscience and Engineering, Faculty of Civil Engineering and Geosciences, TU Delft, the Netherlands. 10 Computational Imaging, Centrum Wiskunde & Informatica (CWI), Amsterdam, the Netherlands. 11 Musical Instruments, Rijksmuseum Amsterdam, the Netherlands.


Complex wooden objects of cultural heritage such as musical instruments present many challenges to the researcher. Particularly keyboard instruments may contain half a dozen different species of wood (some readily identifiable microscopically, others not) from multiple different provenances, many moving parts, overlapping traces of both the tools used during construction and the wear from use, and a variety of physical challenges to the process of examination caused by such factors as the exterior being largely covered in decoration and the interior largely enclosed or difficult to access. This presentation gives an overview of the non-invasive techniques used so far to study the wooden components of one musical instrument: a virginal built in 1640, attributed to Ioannes Ruckers, a member of one of the most important and influential families of plucked keyboard instrument builders in the 17th century. The techniques include microscopy, endoscopy, radiography, dendrochronology and dendroprovenancing, CT scanning, and micro-CT scanning. The authors hope to demonstrate the importance of both simple and well-established techniques as well as the possibilities opened up by more advanced techniques, in the study of wooden musical instruments.


Micro- and sub-µ X-ray CT scanning of Congolese heritage objects for wood identification

Sofie Dierickx1, 2, Wannes Hubau2, 3, Hans Beeckman3, Siska Genbrugge1, Jan van den Bulcke2, 4

1Collection management, Royal Museum for Central Africa, Tervuren, Belgium. 2 UGent-Woodlab, Laboratory of Wood Technology, Faculty of Bioscience Engineering, Ghent University, Gent, Belgium. 3 Wood Biology, Royal Museum for Central Africa, Tervuren, Belgium. 4 UGCT, UGent Center for X-ray Tomography (UGCT), Gent, Belgium.

Knowing the wood species of objects in a museum collection can not only add to the understanding of the objects, but also enable conservators to optimize preservation conditions, and can facilitate international travel of the objects conform the CITES guidelines. To date, the method for identifying African wood species remains an invasive one, permanently removing a part of the object to study its anatomical features microscopically. The TOCOWO project (Tomography of Congolese Wooden Objects) is a collaboration between the Royal Museum for Central Africa (RMCA) in Tervuren, and Ghent University. It aims to explore the potential of micro- and sub-µ X-ray CT as a non-destructive technique for wood species identification of museum objects. At the halfway point of this 2-year research, over 60 Congolese heritage objects have already been scanned, allowing some preliminary conclusions to be drawn about the challenges of scanning fragile and unique collection objects when striving for the optimal resolution for wood species identification. A case study of 3 scanned objects is presented to illustrate the protocol drafted in the framework of the project, detailing the experience of preparing the objects before scanning, acquiring the scans at the UGCT facilities and ultimately processing and analyzing the scans to result in a wood species identification.


Unveiling the hidden world of wood. Just how far can computerized tomography take us in the stuy of wooden carvings?

Emilio Ruiz de Arcaute Martínez1, 2

1Restoration Service, Diputación Foral de Álava, Vitoria, Spain. 2 Research Group HUM956 - Heritage Conservation: Methods and Techniques, University of Seville, Spain.

The study of the constructive technique of images carved in wood has developed into an essential tool to help determine their origin and authorship.

Radiography has traditionally been used as a non-invasive method to examine its structure and the state of conservation. Computerized tomography however allows for a far more exhaustive and exact analysis of its features and system of construction, especially when the structure is very complex having been made from the sum of numerous fragments of wood.

In recent years this study technique has been used occasionally to obtain images for dendochronological dating, but its use is conditioned by the dimensions and complexity of the objects studied.

The conclusions of the research on a group of Flemish reliquaries from the 16th century serve as base for presenting both the potential and limitations in the application of computerized tomography to the study of more complex pieces.


Non-invasive dendrochronology of large wooden objects: complex use of 3D X-ray μCT and microscopic imaging helps to date the Saint Louis sculpture

Rūtilė Pukienė1, Elena Jasiūnienė2, 3, Akmis Lomsargis4, Rapolas Vedrickas5

1Institute of Geology and Geography, Nature Research Centre, Vilnius, Lithuania. 2 Prof. K. Baršauskas Ultrasound Research Institute, Kaunas University of Technology, Kaunas, Lithuania. 3 Department of Electronics Engineering, Kaunas University of Technology, Kaunas, Lithuania. 4 Vilnius Faculty, Vilnius Academy of Arts, Vilnius, Lithuania. 5 Meno kūrinių tyrimai, MB, Vilnius, Lithuania.

Achievements in high resolution 3D computed tomography (μCT) techniques have fostered non-invasive tree-ring analysis of wooden heritage objects. Nevertheless, the size of an object is still a determinant limiting application of micro-tomography. Generally – the bigger the object – the lower achieved resolution. Whereas, the width of tree-rings is crucial factor for image resolution requirements.

We present a case study of non-invasive dendrochronological analysis of a large size (160x70x30 cm) wooden sculpture made of halved Scots pine trunk. Up to recently the Saint Louis sculpture from Vilnius Saint Nicolaus church has been dated by stylistic art-historical evaluation to the 16th or the early 17th century. However, no data has been proving this evaluation.

Investigation of inner structure of the sculpture was carried out using industrial X-ray 3D computer tomograph RayScan 250E. Extended CT mode involving horizontal sideways moving of flat panel detector while rotating the sculpture around its axis allowed to capture approximately 500 mm of the sculpture width. Achieved voxel size of 128 µm suited for discerning annual rings as narrow as 700 µm in the reconstructed transversal images. Series of 111 rings were identified and measured with CooRecorder and dated to 1501-1611AD.

However, visual inspection of the back side of the sculpture has revealed sharp narrowing of rings in the uncaptured side areas. Digital microscope Dino-Lite was used to record ring images in the longitudinal radial plane close to the sculpture edge. In 6.3 cm of this edge zone extra 117 rings were identified, measured and sapwood boundary detected. Consequently, the last ring of the sculpture was dated to 1728 AD.


The use of CT-scan in a dendrochronological study of a dug-out chest

Petra Doeve1

1Dendrochronological laboratory at BAAC Archaeology and Building history, ’s-Hertogenbosch, the Netherlands.

Few medieval dug-out chests have survived in Europe. They were used roughly until the 16th century for storage, when they were replaced by chests made out of boards. Dug-out chests are unique and new discoveries are rare.

Such is the case for the subject of this study: a heavy sized dug-out chest, measuring 140 cm in length, 39 cm in height and 49 cm in width. The question about its age based on art-historical features is a point of debate: is it medieval or from the 16th century?

Tree-ring research on such exceptionally large pieces of furniture can be an impossible undertaking, primarily because the tree rings are out of sight. Tree rings on the interior side of the dug-out chest were analyzed using standard methods of measuring from photos. Non-invasive analysis through CT-scanning ‘exposed’ the tree-rings patterns previously out of sight and additionally allowed us to identify certain features in the woodwork of the chest.

This paper combines conventional and dendro-CT to answer the age question and the provenance of the wood of the chest. The medical CT-scan proved essential in establishing the exact felling date of the oak tree.


WOODAN. Synthesizing data on archaeological wooden objects from Flanders (N-Belgium)

Stephan Nicolaij1, 2, Silke Lange1, 3, Lien Lombaert4, Ignace Bourgeois5, Natalie Cleeren6, Jonathan Jacops4, Koen Deforce7, Kristof Haneca8, Jelte van der Laan1, 9

1WOODAN Foundation, Groningen, the Netherlands. 2 Qursi Software, Groningen, the Netherlands. 3 BIAX Consult, Zaandam, the Netherlands. 4 Erkend Erfgoeddepot Ename, Oudenaarde, Belgium. 5 Provinciaal Archeologisch Depot (PAD), Antwerp, Belgium. 6 Natalie Cleeren Archaeological Conservation, Geetbets, Belgium. 7 Ghent University, Ghent, Belgium. 8 Flanders Heritage Agency, Brussels, Belgium. 9 Cambium Botany, Kleine Huisjes, the Netherlands.

Over the last decades universities, government institutions and commercial companies have collected a huge amount of information on archaeological wooden artefacts. This information is scattered however, and there is no clear overview of what we know about wood utilisation and its development trough time within a larger region. As most publications are focused on specific sites or excavations, it is often hard to place artifacts in a broader context. In 2018 the WOODAN Foundation started collecting data on wooden artefacts with the mission to function as a central platform to find, analyse and publish information on these artefacts.

Thanks to the Flanders Heritage Agency we are enabled to do a big synthetic research project in Flanders. Our goal is to collect all data that is published on wooden artifacts since the Malta agreements, in order to conduct additional research. Also, the WOODAN database <> will be further developed in order to add data and to expand the functionality of translating the data to (for a start) four different languages. In this way language barriers will no longer be an issue in wood research. Our end products of this project will be:

  • A book with an overview of the wooden artifacts found in Flanders

  • The publication of the many finds in the WOODAN database


Measuring curved surfaces using photogrammetry

Sjoerd van Daalen1, Maarten Sepers2, 3

1Van Daalen Dendrochronologie, Deventer, the Netherlands. 2 Department BBT Archaeology, Saxion University of Applied Sciences, Deventer, the Netherlands. 3 DDEA, Deventer, the Netherlands.

Dendrochronology uses tree-ring patterns in wooden objects to determine the age of the wood. In order to obtain an undistorted tree-ring sequence a radius along a transversal surface is preferred. For objects where destructive sampling is possible, this is easily solved by cutting a cross-section or taking a core. More delicate items, such as panel paintings and furniture pieces, are commonly rectangular and provide a transversal section where the tree-rings can be recorded using non-destructive methods. However, in the case of oval shaped painting or sculptures where the base is not usable, it is impossible to find a transversal section. Although tree-rings can be measured along a curved surface, the recorded values will be more distorted as the curvature increases. This renders the outer most tree-ring unusable. While the relative pattern of smaller and wider tree-rings will be preserved, it can no longer be presumed to be an absolute measurement. It is unclear what the effect of the distorted tree-ring pattern will be on the statistical results, especially if the curvature is not uniform. An orthogonal projection of a 3D model of the object creates a distortion-free view of the tree-ring pattern as well as a digital archive of the source data. 3D tomography has been successfully applied for this purpose, but the required equipment is not easily accessible.

In this paper we explore the possibilities of a photogrammetric approach for several case studies as well as propose practical guidelines for the application of this method.


X-ray-CT as possibility to date archived samples from Hallstatt, Austria

Elisabeth Wächter1, Hans Reschreiter2, Kerstin Kowarik2, Michael Grabner1

1Institute of Wood Technology and Renewable Materials, University of Natural Resources and Life Sciences, Vienna, Austria. 2 Department of Prehistory, Natural History Museum, Vienna, Austria.

In Hallstatt countless wooden samples from Bronze age and Iron age (Hallstatt time) are excavated and analysed every year. This is not the case for the subsequent La Tène period. There is only one spot in a raised bog near Hallstatt so called “Dammwiese” (1350 m a.s.l.) where numerous dwelling houses and a tunnel entrance from this period were examined in the 1880s and the first half of the 20th century. Nowadays these sites are not accessible anymore. Nevertheless, a few wood objects like parts of a log cabin, boards, the bottoms of barrels or buckets and fragments of shovels were excavated in former times and are well preserved available in the archive of the Natural History Museum Vienna. It was not desired to cut or drill holes in these unique finds. With the help of X-ray-CT-scans, it was possible to process these samples in a non-destructive way.

In total on 63 wooden elements from four different wood species (beech, spruce, larch and fir) tree-ring width measurements were carried out. Almost half of the measured samples could be synchronized and dated to the time from -263 to -123 resulting in three local mean curves (larch 89 years, fir 243 years and spruce 220 years).

To conclude, it can be worthwhile to take a close look at “old finds” in the archives and do the dendrochronological analyses in a usual way or non-destructively with the help of X-ray-CT-imaging.