State of research

August 1989 at a conference at Källskär, Kökar in the outer Åland archipelago between Finland and Sweden, Åsa Ringbom and Kenneth Gustavsson (Archaeologist at The Åland Museum) were introduced to the method of dating mortar by Högne Jungner of the Dating Laboratory at Helsinki University. The topic of the conference was Fransiscans in Medieval Scandinavia. As a result it was instantly decided that an interdisciplinary team should be formed to develop the method further for dating the stone churches of the Åland Islands. To maximaze the information the dating of the mortar was done parallel to dendrochronology of all the wood available in the churches.

1994 The International Mortar Dating project was initiated as it became obvious that a tandem accelerator was needed to analyse smaller samples and to achieve more precise results. Members of the team: Åsa Ringbom, Alf Lindroos (Åbo Akademi University Finland), Jan Heinemeier (The AMS 14C dating center, Aarhus, Denmark, Högne Jungner (Helsinki University).

1996 As a result of an invitation to Louisville University, Kentucky, the project expanded to Classical Archaeology with Torre de Palma, the largest Roman village on the Iberian Peninsula, Vaiamonte, Portugal. Stephanie Maloney and John R. Hale were included in the team, both from the University of Louisville, KY.

In 1997 the method was also presented at the conference Medieval Europe in Brüges, Belgium. This conference opened for valuable collaboration with Mark Van Strydonck, one of the real pioneers in mortar-dating from the Kikirpa, in Brussels.

1997 at the Annual Meeting of the Archaeological Institute of America in Chicago, our research was presented to a larger audience, among them Lynne Lancaster from the University of Athens, Ohio. She suggested that we should test mortar dating in Rome.

1998 Mortar dating was introduced to pozzolana mortars in Rome, in collaboration with Lynne C. Lancaster, (Classics Department, Ohio University, Athens, OH).

2003 Our team participated with a poster in the conference on Classical Studies in Boston. (poster)

2005 The Oxford Radiocarbon Accelerator Unit, UK became part of our research team when Fiona Brock and Christopher Bronk Ramsay were introduced to test our earlier results in a quest for intercomparison. Thus, some of our earlier results of Pozzolana mortars from Rome were re-analysed.

2006 at a conference in Oxford, Jan Heinemeier presented our research, with the result that Gregory Hodgins joined our team. He represents the NSF-Arizona Accelerator Mass Spectrometry (AMS) Laboratory, University of Arizona. All of this meant that we were gradually set for testing our results with proper inter-comparison between different laboratories and different types of mortars and pozzolanas. Sampling at Herculaneum and Pompeii was tested in 2006. The result from all laboratories involved was that mortars, or pozzolanas that have been buried in volcanic eruptions are not suitable for 14C-analysis.

2007 Mortar dating of the Gotland churches was introduced in collaboration with Joakim Hansson and Heikki Ranta. Gotland is the biggest island in the Baltic Sea, with an incredibly rich history. More than 100 stone churches were being built on Gotland starting roughly 1100AD, all with an individual building history and lavish architectural and artistic embellishments of the highest quality.

2008 The conference Building Roma Aeterna, in joint collaboration between the Finnish Rome Institute, and the American Academy in Rome, was arranged at the Villa Lante, at the Finnish Rome Institute. Program. The Proceedings of Building Roma Aeterna were published in 2011. See the list of publications.

Obviously, all along from the very start in 1989 there here have been numerous minor workshops on mortar dating. But in 2010 First International mortar dating workshop, was arranged in Åbo/Turku and in the Åland Islands. Program.

2011 Cyprus, 14C and Archaeology. Taking an active part in many other conferences widened the circle of scholars interested in mortar dating in a valuable way.

2012 At The Second International mortar dating workshop, arranged in Mallorca by Mark Van Strydonck and the Kikirpa, Brussels, program, the international network was widened to include important collaborators from all over Europe and the US. Many new methods to date mortars were presented. Thus, time had finally come for the most important decision, to start a wide intercomparison program with different mortars in order to find out what method was best suited for dating different types of mortars.

2013 At the 14C and Archaeology in Ghent, Belgium, 6 European countries involved in developing the method could meet for further discussions. One entire session was devoted to mortar dating. Program. [19 Years of Mortar Dating, Learning from Experience.] Glasgow.

2014 at the Annual Meeting in Chicago, the Archaeological Institute of America. Presentation of poster.

2014 The Third International mortar dating workshop, was held in Padova, April 14-16 (organized by Gilberto Artioli – members of Scientific committee ÅR and AL).

2015, Zürich, program

2016 At the 14C and Archaeology conference in Edinburgh, several papers focused on the analysis of lime lumps, and whether they could in any circumstances provide better material than mortar for dating. Could lime lumps for instance be less affected by delayed hardening, could they be less affected by fires and could they include less contamination of unburned limestone? One of the results was that they can indeed be affected by contamination and they therefore need to be separated in many fractions in the preparatory work. That way, age profiles created through many fractions, will reveal the degree of contamination.

2016 At the Historic Mortars Conference, Santorini, Greece, our interdisciplinary testing was presented.

2017 At a small informal workshop in the Åland Islands. Jan Heinemeier, Irka Hajdas, Danuta Michalska, Alf Lindroos, Åsa Ringbom met to discuss on the importance of continuing with the inter-comparison. The fact is that so far our efforts to perform a strict and objective intercomparison has not been enough, partly due to an unfortunate choice of samples. However, the need of 14C inter-comparisons is recognized in many parts of the scientific field, and this is what we intend to continue giving highest priority in the future. Map of European sites where we have been involved in AMS-analysis of different kinds of mortars and pozzolanas.

Forthcoming conferences and workshops:


The 23rd International Radiocarbon Conference will be held in Trondheim, Norway, .


Bordeaux, at this conference we will present the effects of delayed hardening in mortar dating.


Literature in selection:

Hale, J., J. Heinemeier, L. Lancaster, A. Lindroos and Å. Ringbom, Dating Ancient Mortar, American Scientist, Volume 91, 2003: 130-137.

Ringbom, Åsa, Dolphins and mortar dating – Santa Costanza reconsidered, in Songs of Ossian, Festschrift in honour of professor Bo Ossian Lindberg, Taidehistoriallisia Tutkimuksia, 27, Konsthistoriska studier, Helsingfors, 2003, 22-42.

Heinemeier, Jan, Åsa Ringbom, Alf Lindroos, Árný E Sveinbjörnsdóttir: Successful AMS 14C Dating of Non-Hydraulic Lime Mortars from the Medieval Churches of the Åland Islands, Finland. Radiocarbon, Vol 52, Nr 1, 2010.

Building Roma Aeterna. Current research on Roman Mortar and Concrete. Proceedings of the conference March 27-29 2008. Editors Åsa Ringbom and Robert L. Hohlfelder, Assistant editors Pia Sjöberg and Pia Sonck-Koota, Commentationes Humanarum Litterarum 128 2011. Societas Scientiarum Fennica. 258 pages. ISBN 978-951-653-348-4.

Ringbom, Å., Lindroos, A., Heinemeier, J., Sonck-Koota, Pia, 19 years of mortardating – learning from experience. Proceedings from the 7th Conference on 14C and Archaeology, Ghent April 2013, Radiocarbon, Vol 56, Nr 2, 2014. p 619-635. [PDF copy available]