Sticking stones: Rediscovering medieval wood tar adhesives for stone conservation

Updates from the project

February 2026

Aachen Cathedral research visit

Earlier this month, Bettina, Silas and Paul visited Aachen Cathedral in Germany to experiment with the practical application of wood tar adhesives and to collect historical samples. Together with the expert stonemasons at Schwartzenberg, we mixed different adhesives and practiced glueing replica stone indents on a test piece specially prepared by Schwartzenberg. This provided valuable experience which helps us understand what working properties are important for the adhesives, and what application techniques work best and might have been used in the past.

After a full day of experiments, we visited Aachen Cathedral for a special tour by Jan Richarz, head of the cathedral workshop. Silas and Bettina collected a sample of adhesive dating from the early 13^th Century, which will be sent to Joy and Ingunn for further analysis and characterization. This will greatly improve the breadth of knowledge on historic adhesives materials by further expanding the Sticking Stones archaeological reference collection.

During the sampling, we were also interviewed by reporters from the newspaper “Aachener Zeitung” and the radio station “Antenne Aachen”. Follow the links to see their coverage!

November 2025

Project dissemination activities, autumn 2025

In the autumn, we undertook a range of dissemination activities.

Bettina and Silas presented the Sticking Stones project to delegates of the British-European Cathedrals Conference, or Dombaumeistertagung in London in late September. The presentation was received with enthusiasm, and many new collaborations and connections with a range of cathedral workshops across Europe were formed as a result.

We also had the opportunity to attend several exciting site visits to cathedrals in London, and were successful in our hunt for stone adhesives.

The research project was also presented to the general public in Stavanger as part of the National Science Fair, Forskningsdagene, with a stall and children's activities.

In October, the project group also had a poster presentation, while Silas gave a talk at the Biennial International Conference for the Craft Sciences in Mariestad, Sweden. During November, Bettina gave a talk about the research project to Forsvarsbygg, the Norwegian Defence Estates Agency.

September 2025

Sample preparation for mechanical testing is underway at the Department of Architectural Engineering and Technology, TU Delft

Mechanical testing of adhesives on stone provides a unique challenge. Tests need to be repeated dozens of times to account for the variable nature of the material. This requires hundreds of precisely cut sample pieces before the tests can even begin.  

Using a special diamond-bladed wet saw (the Qcut 400 A) at the Geosciences and Engineering Laboratory at TU Delft, Paul Kozowyk cut soapstone collected from the medieval quarry used to build Stavanger Cathedral. The stone was cut into identical test pieces, matching the sizes required by international adhesive testing standards (ISO). 

Now that the first stage in sample preparation is completed, different adhesive formulations based on archaeological material and historical texts will be prepared. Finally, the soapstone samples will be glued together and tested for both the shear and tensile strength of the adhesive joints. This will tell us how different wood tar adhesive recipes perform; shedding light on medieval knowledge and aiding the development of traditional materials for future conservation work.  

June 2025

Opening of jubilee exhibition, The Cathedral's secrets: Stavanger Cathedral 1125-2025

On the 6th of June, a new exhibition opened at the Museum of Archaeology. The exhibition celebrates the cathedral restoration project, and highlights latest research on the cathedral and the city's medieval past.

Bettina has been one of the experts in charge of the content, and has worked behind the scenes right from the start, handling excavation, conservation, research and documentation of some of the finds exhibited.

Material and knowledge connected to or derived via the Sticking Stones project are included in the exhibition. Medieval scaffolding timbers from the cathedral are on view, as well as medieval tar and stone adhesive repairs undertaken during the Gothic construction period. Our latest research regarding dating of the cathedral's Gothic sections has been utilized to create a revised timescale. Medieval treasures discovered underneath the cathedral sacristy have been displayed for the first time since their excavation in 2024.

March 2025

Presentation for NIKU

In March, Silas presented his research plan at the Norwegian Institute for Cultural Heritage Research (NIKU) in Oslo.  NIKU is an independent institute for applied R&D and services within the wider field of Cultural Heritage in Norway and beyond.

The aim of this get-together was to present his planned PhD research as part of the Sticking Stones project, to benefit from all the assembled knowledge and experience of colleagues working in neighbouring fields, and to make new contacts.
Having representatives from NIKU, Riksantikvaren, Fortidsminneforeningen, NordicTarNetwork, NorskHåndverksinstitutt, Nasjonalmuseet and restoration companies present shows the great and diverse interest in the topic. Thank you all for participating and sharing your knowledge!

January 2025

Visit from Trondheim

In January, we held our second successful collaboration meeting with our colleagues from Nidaros Cathedral Restoration Workshop (NDR) in Trondheim. This time the meeting took place in Stavanger at the Museum of Archaeology.

We presented the Sticking Stones project in detail and then went for a site visit to take a close look at Stavanger Cathedral. Our aim was to exchange ideas with other stonemasons at a professional level. Did they make similar observations in Trondheim? How would they approach historic stone carvings today? Would Nidaros Cathedral be a suitable case study?

Thank you very much for the valuable insights and the friendly visit. See you soon!

September 2024

Participation at a conservation congress in Lima

The Museum of Archaeology recently had the privilege of being represented (for the first time in its history!) with a paper presentation at the International Institute for Conservation’s (IIC) Congress in Lima, Peru. This takes place every other year, and is globally one of the most important events in conservation.

The IIC Congress is a global arena for intellectual exchange and dissemination within the wider conservation discipline. The theme was 'Sustainable Solutions for Conservation: New Strategies for New Times'. Therefore, this was an apt venue for Bettina to present her ongoing research project Sticking Stones. Bettina received a dissemination grant from the EU COST Action POTARCH to travel to Peru and present her paper in-person in Lima.

At the much-anticipated global event that is the IIC Congress, thousands of conservation practitioners, academics, researchers and policy makers gather to address challenges and solutions for the discipline. The scientific program is curated by an international committee that selects circa 40 of the most promising abstracts from many hundred submissions. Selected paper presenters are invited to write a peer-reviewed publication that is published in a special issue of the discipline’s most important and respected journal, Studies in Conservation.

Bettina’s open access publication in Studies in Conservation has proven to be very popular, as it is currently the most read paper in the special issue, with over 1000 reads after such a short time! It was a real privilege to represent the University of Stavanger and the Sticking Stones project on this important stage.

November 2024

Startup meeting in Stavanger

The research group gathered in Stavanger in November 2024 for the kickoff meeting. We had a few intense days getting to know one another, discussing ideas and making plans for the next year.

Exciting times ahead!