14C dating of lime mortar – preparation of the sample, a challenge for the geologist and the mineral chemist

Lime mortar from old constructions can he successfully dated using the 14C method if special care is taken during sampling and sample preparation. The main problems with dating is identification and removal of fossil limestone in the filler. Especially in limestone areas contamination from filler limestone can be severe. Proper identification of the contaminants enables us to develop optimal laboratory protocols for sample handling. Contaminants including limestone and marble filler material, incompletely burnt limestone residues, and recrystallisations in the mortar can be identified in thin sections of intact mortar samples and in the fine fractions of crushed mortars using polarising microscopy and cathodoluminescense. Careful crushing and sieving of the mortar samples, however, effectively removes limestone grains and particles. The proportion of limestone contaminant in the samples can be assessed by traditional point counting or computer image analysis of luminescence micrographs. A sufficient number of samples from each construction phase are needed for statistical significance of the dating

Optimisation of the radiocarbon dating process of mortar samples. A case study in the Colosseum, Rome (Italy)

This project highlights the importance of an integrated planning of field and laboratory procedures for the success of the radiocarbon dating of mortar samples. In this research bulk mortar analysis was complemented with lime lump analysis. The two materials were dated at different laboratories. Results are discussed considering the historic and archaeological information available on the building and on the structure where the sample was collected

Projektet Ålands kyrkor och murbruksdatering – rapport från en metodutveckling

The Åland Churches and Mortar Dating – State of Research from the Development of a Method. By Åsa Ringbom, Jan Heinemeier, Alf Lindroos & Àrny Sveinbjörnsdottir. Why mortar dating? The project the Åland Churches was initiated with the aim to finally reach a reliable chronology for a group of stone churches upon which there had been deep disagreement. Since there are no contemporary sources to shed light on the matter, and since coins and artefacts cannot date buildings, there was an obvious need for objective scientific methods on a larger scale. The method of dendrochronology was widely applied on wooden structures in the churches in 1991-1992. Even if dendrochronology could not date the first building stages of the churches, due to repairs and fires, this method was very important in providing firm dates for secondary structures, and for comparative research. Mortar is not an organic material. Yet, absorbing CO2 from the atmosphere during the hardening process, makes mortar an ideal material for 14C dating. Compared to all other datable materials, mortar has the advantage of being found in the original in large quantities, from all the different building stages. Thus, the project focused on developing the method of mortar dating. Since 1994, reliable results have been reached, thanks to the introduction 14C AMS (Accelerator Mass Spectrometry) analysis. To begin with the analysis took place in the 14C AMS Dating Centre at Aarhus University, Denmark. The project turned international in 1997 when the method was tested in classical archaeology, upon mortars from the margins of the Roman Empire, and on hydraulic pozzolana mortars from Rome itself. Since 2005 the collaboration for the analysis includes the Oxford Radiocarbon Accelerator Unit, and the NSF-Arizona AMS Laboratory, in Tucson. Our conclusion today is that non hydraulic lime mortars, whether medieval or classical, are well suited for mortar dating. From Åland, 96% of all the mortars with age control, have yielded convincing results (for further information see www.kyrkor.ax). It is hardly surprising that hydraulic pozzolana concrete, with an entirely different chemistry, is more difficult. But even so, several important structures in Rome have yielded an age well known from historical sources and brick stamps. From our vast experience we have been able to identify different criteria of reliability for interpreting results where mortar dating is the only method available

Om datering av Gotlands medeltida kyrkor

About Dating the Medieval Churches of Gotland By Heikki Ranta, Joakim Hansson, Alf Lindroos, Åsa Ringbom, Jan Heinemeier, Fiona Brock & Gregory Hodgins In 2006 the project »Mortar dating of the Gotland churches« was initiated, with the aim to test how mortar dating would work in a geological area so dominated by Silurian limestone, and how the results of this method could affect the prevailing chronology of the churches. Initial testing was done on three different churches, the church of Bro in the northern part of the island, and with Hamra and Vamlingbo in the south. The result is that mortar based on Silurian limestone behaves much the same way as mortar including Åland Ordovician limestone. Thus, based on mortar dating a chronology of the church of Bro can be seen as follows: A Romanesque nave from ca AD 1040-1160, with an almost contemporary tower in the west, with an additional chancel in the east from the 13th century. In the church of Hamra, the lower part of the west tower, and possibly also the earlier part of a cruciform plan, dates from 1165-1220. Later, in 1260-80, the tower was heightened. The chancel in the east is an addition from the 14th century. In Vamlingbo, the focus was on a secondary support construction of disputed age, built against a south portal. This time the mortar was contaminated by unburned limestone, and the result of mortar dating remains inconclusive. However, fragments of wood and charcoal, incapsuled in the mortar, suggest a terminus post quem some time in the 14th century. It is most likely that the supporting wall is a medieval construction. At this initial stage it seems that the results of mortar dating in turn support earlier prevailing views on the chronology. The results also coincide with occasional dendrochronological dates and with contemporary inscriptions in the churches. It seems that mortar dating can be a helpful tool in forming an objective base for a chronology of the Gotland churches

Radiocarbon dating historical mortars: lime lumps and/or binder carbonate?

Lime lumps and bulk mortars show different 14C contamination when analyzed in several CO2 fractions isolated from the effervescence of an ongoing hydrolysis reaction. Age profiles of both materials are therefore highly complementary and together they can provide a reliable date. Furthermore, they can also reveal the complexity of the radiocarbon (14C) distribution within the mortar and thus prevent over-interpretation of the data. The lime lump versus bulk mortar dating data presented here has been collected over 22 years, with only a small fraction of the results so far published internationally. Since there has been an increasing interest in mortar dating over recent years with a special focus on lime lumps, and since many laboratories have just begun mortar dating experiments, we wish to present some of the extensive data that already exist. Previously published data from 15 lime lumps (including 34 14C measurements from sequential dissolution) and 43 new 14C measurements from 17 lime lumps are presented here. The samples are from medieval Finland and Sweden, classical Rome and medieval Italy, and the Roman Jerash (Gerasa), Jordan

Successful AMS 14C Dating of Non-Hydraulic Lime Mortars from the Medieval Churches of the Åland Islands, Finland

Fifteen years of research on accelerator mass spectrometry (AMS) radiocarbon dating of non-hydraulic mortar has now led to the establishment of a chronology for the medieval stone churches of the land Islands (Finland), where no contemporary written records could shed light on the first building phases. In contrast to other material for dating, well-preserved mortar is abundantly available from every building stage. We have gathered experience from AMS dating of 150 land mortar samples. Approximately half of them have age control from dendrochronology or from 14C analysis of wooden fragments in direct contact with the mortar. Of the samples with age control, 95% of the results agree with the age of the wood. The age control from dendrochronology, petrologic microscopy, chemical testing of the mortars, and mathematical modeling of their behavior during dissolution in acid have helped us to define criteria of reliability to interpret the 14C results when mortar dating is the only possibility to constrain the buildings in time. With these criteria, 80% of all samples reached conclusive results, and we have thus far been able to establish the chronology of 12 out of the 14 churches and chapels, while 2 still require complementary analyses.The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

Mortar Dating Using AMS 14C and Sequential Dissolution: Examples from Medieval, Non-Hydraulic Lime Mortars from the land Islands, SW Finland

Non-hydraulic mortars contain datable binder carbonate with a direct relation to the time when it was used in a building, but they also contain contaminants that disturb radiocarbon dating attempts. The most relevant contaminants either have a geological provenance and age or they can be related to delayed carbonate formation or devitrification and recrystallization of the mortar. We studied the mortars using cathodoluminescence (CL), mass spectrometry (MS), and accelerator mass spectrometry (AMS) in order to identify, characterize, and date different generations of carbonates. The parametersdissolution rate, 13C/12C and 18O/16O ratios, and 14C age were measured or calculated from experiments where the mortars were dissolved in phosphoric acid and each successive CO2 increment was collected, analyzed, and dated. Consequently, mortar dating comprises a CL characterization of the sample and a CO2 evolution pressure curve, a 14C age, and stable isotope profiles from at least 5 successive dissolution increments representing nearly total dissolution. The data is used for modeling the interfering effects of the different carbonates on the binder carbonate age. The models help us to interpret the 14C age profiles and identify CO2 increments that are as uncontaminated as possible. The dating method was implemented on medieval and younger mortars from churches in the land Archipelago between Finland and Sweden. The results are used to develop the method for a more general and international use.The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

14C Dating of Fire-Damaged Mortars from Medieval Finland

This study focuses on radiocarbon dating of mortars that have withstood city fires and display visible fire damage effects. Some fire-damaged and undamaged original Medieval mortars from the same site have also been tested. The mortars were heated at different temperatures and then analyzed using the same preparation procedures as in 14C dating of mortars to see what kind of changes the heating would introduce to the mineralogy, chemistry, and the carbon and oxygen isotope ratios. We found that decarbonation during heating starts at ~600 °C and recarbonation starts as soon as the temperature drops. Already after a few days, most of the lost CO2 has been replaced with atmospheric CO2. The renewed carbonates are readily soluble in the acid hydrolysis process and their carbon and oxygen isotopes have a light signature. Fire-damaged historical mortars display the same features. If a long time has elapsed between hardening of the original mortar and the fire, the new carbonates have 14C concentrations that point to the fire event rather than to the building event. In several cases, the fire-damaged mortars have an easily soluble carbonate fraction with a 14C age that could be related to a major fire event, but still most of the soluble carbonate yields a 14C age that seems like a reasonable age for the original construction.The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

The Roman amphitheatre in mérida, Spain ˗Augustan or Flavian? Radiocarbon dating results on mortar carbonate

Four lime mortar samples from the Mérida amphitheatre in Spain were dated in 2001 and re-dated in 2019 with refined dating methods and focus on carbon dioxide that was released in late CO2 fractions when dissolved in phosphoric acid. The samples were difficult to date because they contained highly soluble, young carbonate contamination that dominated the carbon dioxide from the early stages of the reaction with the acid in the hydrolysis process. They were also rather hydraulic and rich in magnesium, which could have caused delayed hardening. However, there was very little dead carbon contamination so that late carbon dioxide fraction gave uniform 14C ages, pointing to a late 1st c. AD Flavian, or later age of the amphitheatre.ISSN:1733-8387ISSN:1897-169