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Radiocarbon dating mortar: The identification of a Medieval Irish round tower using a multi-method inter-comparative approach
Abstract
Investigations were carried out to establish the chronology of a building from the city of Derry, Northern Ireland. The date of this structure, previously assumed to be a 17th century windmill, was examined by application of radiocarbon dating to the lime mortar. Multiple sample preparation methods (cryo-breaking, mechanical, suspension) were used to isolate a series of lime binder fractions of different grain sizes. Combined with sequential dissolution and subsequent radiocarbon dating this permitted a) the presence of multiple carbonate components to be identified and, b) aided by inter-comparison of the dissolution profiles and the presence of well-defined plateaus in the age profiles, those components and dates associated with the building’s construction to be resolved. Interpretation of the results was further enhanced by assessing the efficacy of preparations methods through application of particle size analysis, x-ray diffraction, thermogravimetric analysis and Fourier transform infrared spectroscopy. This work revealed that the building can now be recognized as the remains of a mid to late 13th century Irish round tower and, as such, the only building surviving from the Derry’s Medieval monastic era, therefore making it of great cultural and historical significance.
... In the past few decades, the dominant method for extraction of CO 2 from lime binder has involved acid dissolution methodologies, more specifically sequential dissolution where multiple fractions are taken from a single sample to be dated (e.g. [13][14][15][16][17][18][19][20][21][22] ). Recently however, the application of thermal decomposition to mortars has also been re-examined as a means of reducing or removing contaminating components [23][24][25] . ...
... Radiocarbon dating of RP samples was carried out at 14 CHRONO Centre (Queen's University Belfast) using an IonPlus MICADAS. HOXII (SRM 4990C NIST) was used for normalization with background corrections carried out following Keaveney et al. [26] . ...
... Unfortunately, characterization (e.g. FTIR, XRD that would be carried out on binder prepared from bulk as per [14] ) was not conducted on the samples. Because the quantity of material available per sample was limited and the carbon content of each sample was unknown at the outset, retaining all material to optimize the number of RP fractions and quantity of CO 2 trapped was prioritized; this also served to minimize the risk of introducing contaminants or inducing secondary crystallization by breaking up the sample and exposing unreacted surfaces (e.g. if portlandite was present). ...
... This structure, located in the city of Derry, Northern Ireland, was until recently considered to be the remains of a 17th century windmill. However, recent work using conventional mortar dating methods demonstrate that the tower is, instead, composed of the remains of a 13th century monastic round tower, later modified and reused (Barrett and Donnelly, 2019;Barrett et al., 2020). Mortar samples from this previous work were used in the current study. ...
... Mortar samples from this previous work were used in the current study. These samples had been subjected to pre-treatment methods to refine a fractions size of <38 μm and have also previously been characterized by particle size analysis, thermogravimetric analysis, XRD and FTIR, where support was found for the presence of unburnt limestone and secondary calcite (Barrett et al., 2020). ...
... However, the sample Kim underwent no pre-treatment and is a raw lime lump that had been imbedded in a bulk mortar; in this case, the sample is likely to have had low levels of limestone/unburnt limestone contamination to begin with, with the results also having benefited significantly from the selection of temperature fractions on the low end of the CO 2 profile, thus minimizing the contribution from limestone/unburnt limestone contamination (see modelling results discussion below). As well as this, samples LCCA and Kim are also likely to have had low levels of secondary calcite present (Barrett et al., 2020;Daugbjerg et al., 2021b). ...
Current methodologies for radiocarbon dating of mortars typically use mechanical and chemical separation to isolate fractions of carbon dioxide from suitable lime binder carbonates. These methods have a moderate frequency of success, but difficulties are often encountered with (a) secondary crystallisation, (b) the presence of incompletely burnt limestone or limestone aggregate, and (c) more complex hydraulic mortars (e.g. pozzolana or cocciopesto mortars). An alternative approach to isolating CO2 from mortar involves thermal decomposition of the sample.
A new ramped pyroxidation (RPO) facility has recently been constructed at the ¹⁴CHRONO Centre. In RPO, samples are incrementally heated, with CO2 produced as the sample undergoes thermal decomposition in the presence (oxidation) or absence (pyrolysis) of oxygen. The CO2 evolved from different temperature fraction are collected cryogenically and radiocarbon dated. This method was applied to several lime mortars with expected ages to investigate if CO2 fractions only associated with the setting of the lime binder could be isolated.
For all samples tested, positive results were obtained. All but the first of six CO2 fraction taken during the earlier stages of thermal decomposition were in statistical agreement and could be combined to provide an age that was in excellent agreement with the expected ages (for an Irish medieval round tower, and for a Finnish medieval castle and church). The lowest temperature fraction, not in statistical agreement, is significantly earlier and attributed to contamination from charcoal or coke from lime production. Positive results were also obtained from a piece of mortar that had undergone no pre-treatment.
Modelling examining the potential of RPO to isolate lime binder CO2 fractions, where either limestone (or incompletely burnt limestone) or secondary re-crystallised calcite are present as contaminants, further demonstrate the suitability of the approach.
... Using petrography, Nonni et al. (2018) identified secondary calcite attributed to groundwater in buried mortar from the Temple of Minerva Medica, Rome, and found contamination of old material in the radiocarbon results. Meanwhile, some studies with above ground sampling do not report groundwater issues (Heinemeier et al. 2010;Pesce et al. 2012;Barrett et al. 2020a). ...
... Further characterization methods in mortar dating studies have also proven useful for the identification of possible contaminants (Fig. 4). Examples are X-ray diffraction (XRD) (Ponce-Anton et al. 2018), optical microscopy (Pesce et al. 2009), stable isotopes Van Strydonck et al. 1986;Ambers 1987), thermogravimetric analysis or differential scanning calorimetry (TGA/DSC) (Ponce-Anton et al. 2018;Michalska 2019), Fourier-transform infrared spectrometer (FTIR) (Chu et al. 2008;Poduska et al. 2012), leach rates (Lindroos et al. 2007;Michalska and Czernik 2015), inductively coupled plasma mass spectrometry or inductively coupled plasma optical emission spectrometry (ICP-MS/OES) (Al-Bashaireh 2016; Barrett et al. (2020a). Sample from Lumen Christi, Northern Ireland, UK. [Colour figure can be viewed at wileyonlinelibrary.com] ...
... The cryo-breaking method aims to improve the mechanical separation of binder material compared with conventional crushing of samples (Marzaioli et al. 2011;Michalska et al. 2017). Some studies use cryo-breaking and report accurate results (Marzaioli et al. 2011;Michalska et al. 2017;Barrett et al. 2020a). ...
Radiocarbon dating of mortars is a method for absolute dating of historical mortared stone structures. Successful mortar dating studies have answered chronological questions, while other studies have revealed that mortar samples can have complications and contaminants. These can cause inconclusive results even with present state‐of‐the‐art techniques. Previous research shows that adequate and proper sampling of mortar samples is of fundamental importance for a conclusive radiocarbon analysis. Therefore, this article thoroughly reviews the processes and environmental factors that may cause problems for successful radiocarbon dating of mortar samples, and it presents best‐practice sampling‐strategies for radiocarbon mortar dating.
... The results obtained are compared to the consensus values presented at the Radiocarbon conference in Zürich in September 2022. A final discussion lays out the strengths and limitations of the thermal decomposition approach for mortar dating (Barrett et al. 2020;Daugbjerg et al. 2021). ...
The absolute dating of mortar by accelerator mass spectrometry (AMS) has been the subject of renewed interest for several years. International intercomparison campaigns, called MODIS (MOrtar Dating Intercomparison Study), have been carried out. The first MODIS-1 campaign highlighted limitations in mortar dating, due to the similarity between the primary material to be dated (binder) and the contaminant (exogenous CaCO 3 ). Methods have since emerged to overcome this problem and the need for a good preliminary characterization has been proven. The Laboratoire de Mesure du Carbone 14 (LMC14) took part in the second intercomparison campaign, MODIS2, by applying thermal decomposition increments to distinguish the carbonated binder, the organic matter contaminants (late in formation pyrogenic carbonate, LDH) and limestone. The LMC14 results on MODIS2 are quite conclusive on “pure” re-carbonated lime mortar binders containing little contaminant geological limestone but show their weaknesses for mortars heavily contaminated in Dolomites, which are difficult to discern from the binder. Recommendations for users of radiocarbon ( ¹⁴ C) dating on mortar-based materials are made in the conclusion.
... We find two possible origins for these particles. One is char mixed in the plaster, a common historical procedure (Barrett et al., 2020). The other is a possible natural or man-made resin reinforcement used in the plaster. ...
Microbial activity following invasion of human-made structures and artifacts can have profound social and economic consequences including the permanent loss of cultural heritage. The unique frescoes in the 11th century Saint Sophia's Cathedral (Kyiv, Ukraine) have recently suffered from dark-spot biodeterioration. The aim of this work was to elucidate the microbial nature of biodeterioration and the biogeochemical processes occurring in the areas of the dark spots. Culture-independent approaches including scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), micro-X-ray diffraction and real-time quantitative polymerase chain reaction (qPCR) analysis were used in this study. SEM and qPCR data demonstrated that the main agents of fresco biodeterioration were mycelial fungi, with bacteria unlikely to play a major role in the development of the dark spots. SEM-EDS results showed that fungi colonization of the dark spotted areas resulted in mechanical and chemical weathering involving dissolution of mineral components of the plaster (mainly calcite) and displacement of mineral grains, which compromise the stability of the plaster or fresco. SEM-EDS also detected fungal biomineralization of secondary mycogenic minerals: calcium malate, hydrated aluminium and ferric phosphates. Biomineralization of calcium malate by fungi, as found in this study, is a rare biogeochemical phenomenon, possibly linked to the presence of calcite and nitrogen limitation.
... The cryo2sonic protocol pre-treated samples as described by Marzaioli et al. (2013), Nonni et al. (2013) and Barrett et al. (2020). Here an ultrasonic bath produced small particles from a cryogenically broken sample suspended in ultrapure water. ...
Ancient Gerasa (its Greco-Roman name)/Islamic Jerash (its later Arab name) is one of the most well-known pre-modern urban sites in northern Jordan, which flourished throughout antiquity and into the early Islamic period. Direct dating of mortar and plaster in Jerash is challenging due to the area’s abundance of geological carbonates that hamper the use of radiocarbon mortar methodologies as shown by previous attempts. Therefore, this study revisited the important problem of Jerash mortar dating. The aim was to advance solutions to the challenges with geological carbonates through sample pre-treatment and preparation methods such as wet sieving, sedimentation, cryo2sonic and stepwise injection of diluted acid. To characterize the samples we used alkalinity screening and cathodoluminescence microscopy. Ten plaster samples from an Umayyad house, destroyed by the earthquake in 749 CE, in Jerash were radiocarbon dated. These produced 12 conclusive dates out of 20 attempted datings, and here some samples had multiple attempted datings. These dates confirmed the early Islamic date of the house structure, while some samples suggested reuse of older material. Five comparative mortar samples from medieval Finland and Sweden critically evaluated the methodology proposed in this article. These have known ages, and they produced five conclusive dates that compared accurately with the expected ages. Compared to previous attempts at Jerash mortar dating, this study made substantial contributions to Jerash mortar dating.
The Second International Mortar Dating Intercomparison Study (MODIS2) took place in 2020. Three mortar samples from different sites and chronologies were distributed among various research groups in form of bulk mortar and grain fraction smaller than 150 µm. This is the first time the Zagreb Radiocarbon Laboratory, with support of the Center of Applied Isotope Studies, University of Georgia, took part in the international mortar intercomparison. The initial approach of the Laboratory to mortar dating was to separate 32–63 µm grain fraction and collect three CO 2 gas portions by sequential dissolution with acid. After checking the ¹⁴ C date trends of the gas portions, which should be ascending with later fractions, the one for the first and shortest gas portion was reported as the age of the mortar. However, the first gas portion might not be true age of the mortar, since it still might contain some “dead” carbon. Therefore, data extrapolation from the first two initial CO 2 portions was also conducted on the results, but not reported to the intercomparison. Though in general, all the intercomparison reported dates fit the expected historical ages, for one sample, the extrapolated result showed a better match to the historical data.
This paper considers how the data returned by radiocarbon analysis of wood-charcoal mortar-entrapped relict limekiln fuels (MERLF) relates to other evidence for the construction of medieval northern European masonry buildings. A review of previous studies highlights evidence for probable residuality in the data and reflects on how this has impacted on resultant interpretations. A critical survey of various wood-fired mortar materials and lime-burning techniques is then presented, to highlight evidence suggesting that a broad spectrum of different limekiln fuels has been exploited in different periods and that growth, seasoning, carriage and construction times are variable. It is argued that radiocarbon analysis of MERLF fragments does not date building construction directly and the heterogeneity of the evidence demands our interpretations are informed by sample taphonomy. A framework of Bayesian modelling approaches is then advanced and applied to three Scottish case studies with contrasting medieval MERLF assemblages. Ultimately, these studies demonstrate that radiocarbon analysis of MERLF materials can generate reasonably precise date range estimates for the construction of medieval masonry buildings which are consistent with other archaeological, historical and architectural interpretations. The paper will highlight that these different types of evidence are often complementary and establish that radiocarbon dated building materials can provide an important focus for more holistic multidisciplinary interpretations of the historic environment in various periods.
Mortars from different stratigraphic units at Portilla Castle (Alava, North Spain) have been analyzed for mineralogical characterization before radiocarbon dating. The mortar binder at Portilla Castle is composed not only of neoformation calcite but also of double-layered hydroxide (LDH) minerals such as hydrotalcite and hydrocalumite. The mineralogy of several fractions of the binder has been analyzed to determine the granulometric distribution of minerals in the binder. The continuous monitoring of mineralogy during the extraction of different grain size fractions has been performed by using a scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermogravimetric analyses (TGA). Hydrotalcite and hydrocalumite-bearing mortar binders give older ages than expected since they introduce dead carbon into the system.
Lime lumps and bulk mortars show different ¹⁴ C contamination when analyzed in several CO 2 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 ( ¹⁴ C) 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 ¹⁴ C measurements from sequential dissolution) and 43 new ¹⁴ C 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.
Seven radiocarbon laboratories: Åbo/Aarhus, CIRCE, CIRCe, ETHZ, Poznań, RICH, and Milano-Bicocca performed separation of carbonaceous fractions suitable for ¹⁴ C dating of four mortar samples selected for the MOrtar Dating Inter-comparison Study (MODIS). In addition, optically stimulated luminescence (OSL) analyses were completed by Milano-Bicocca and IRAMAT-CRP2A Bordeaux. Each laboratory performed separation according to laboratory protocol. Results of this first intercomparison show that even though consistent ¹⁴ C ages were obtained by different laboratories, two mortars yielded ages different than expected from the archaeological context.
This paper reports the results from applying the Cryo2SoniC (Cryobreaking, Sonication, Centrifugation) protocol to some lime mortars sampled from the citadel of Shayzar (Syria). The overall aims of this project are 1) to use the properties offered by high-precision accelerator mass spectrometry (AMS) radiocarbon dating for the evaluation of absolute chronology with its typical robust time constraints (i.e. 25 ¹⁴ C yr), and 2) to apply the dating directly to the citadel structures in order to prevent possible biasing effects potentially affecting indirect ¹⁴ C dating on organic materials found at the study site. The analyses presented in this paper have been mainly performed as a preliminary check of the Cryo2SoniC methodology in order to assess its applicability to this study site by comparing observed mortar results with archaeological expectations about the citadel development phasing and charcoals found encased in mortars. Petrographic and mineralogical thin-section analyses by optical microscopy (TSOM), X-ray powder diffraction (XRD), and scanning electron microscopy plus energy dispersive spectroscopy (SEM/EDS) investigations were carried out for characterization of the mortar samples to verify the occurrence of some features, related to their production technology, which may introduce dating offsets. The resulting ¹⁴ C calibrated ages were in agreement with the archaeological expectations based on type and stratigraphic site reconstructions, in situ inscriptions, and written sources. Such results showed also a general (with 1 exception) statistical agreement among the charcoals and the analyzed mortars simultaneously, confirming the archaeological expectations for the Shayzar citadel. Results presented in this paper indicate good accuracy for the applied procedure for chronology reconstruction and highlight the capability of Cryo2SoniC to further characterize the Shayzar site.
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 Åland 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 Åland mortar samples. Approximately half of them have age control from dendrochronology or from ¹⁴ C 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 ¹⁴ C 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.
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 14 C 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 ° and recarbonation starts as soon as the temperature drops. Already after a few days, most of the lost CO 2 has been replaced with atmospheric CO 2 . 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 14 C 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 14 C age that could be related to a major fire event, but still most of the soluble carbonate yields a 14 C age that seems like a reasonable age for the original construction.
Since 1994, our team has gained extensive experience applying accelerator mass spectrometry (AMS) radiocarbon analysis for mortar dating, totaling over 465 samples and 1800+ measured CO 2 fractions. Several samples have been analyzed repeatedly. The research covers both Medieval and Classical archaeology. We therefore believe our experience can be helpful when developing preparation procedures for different kinds of mortars in different areas and in varying chronologies. So far, the main areas of interest have been (a) the churches of the Åland Islands (in the archipelago between Finland and Sweden); (b) the churches in the Åboland Archipelago (SW Finland); (c) sites in the Iberian Peninsula including Torre de Palma (a Roman village in Portugal); and (d) Rome, Pompeii, and Herculaneum (Italy). Most of the analyses before 2000 were hydrolized in only two CO 2 fractions per sample, and reliability criteria were defined on the basis of how well the ages of the two fractions agree with each other. These criteria have proved most helpful in determining the reliability of 14 C mortar analyses. Different types of mortar have been investigated, including lime mortars made both from limestone and marble, pozzolana mortars, fire-damaged mortars, and mortars based on burnt shells. Most importantly, separate lime lumps sampled from these mortars have been analyzed sporadically and recently more systematically. The research also includes different types of hydrolysis applied in the pretreatment. In addition to using 85% phosphoric acid (H 3 PO 4 ), the experimental research includes tests with smaller concentrations of phosphoric acid, and tests based on 2–3% hydrochloric acid (HCl) dissolutions. To characterize the dissolution process, results are presented as age profiles of 2–5 CO 2 fractions. In our experience, pozzolana mortars have been difficult to date, and HCl dissolution should be used only in special cases and in complementary tests.
This paper deals with the potentialities and technical and methodological issues associated with the use of lumps of not completely melted lime as material suitable for the radiocarbon dating of aerial lime mortars and plasters. In fact, the identification and selection of single aggregates of unmelted lumps allows one to reduce the possible contamination resulting from external sources of carbon such as “ 14 C-dead” limestone in sand added to the mixture during preparation. This procedure results in the possibility for accurate 14 C determinations from single pieces of masonry, supplying important information about the construction phases of historical buildings. The potential of this approach is shown by presenting the results of the archaeological study on the walls of San Nicolò of Capodimonte church (Camogli, Genoa, Italy), where this technique has been successfully applied to obtain absolute ages of different parts of the building. The obtained results were then compared with the information gathered from historical sources and with stratigraphic and other archaeological studies.
Count rates, representing the rate of 14 C decay, are the basic data obtained in a 14 C laboratory. The conversion of this information into an age or geochemical parameters appears a simple matter at first. However, the path between counting and suitable 14 C data reporting (table 1) causes headaches to many. Minor deflections in pathway, depending on personal interpretations, are possible and give end results that are not always useful for inter-laboratory comparisons. This discussion is an attempt to identify some of these problems and to recommend certain procedures by which reporting ambiguities can be avoided.
The remains of Vindonissa, the Roman legionary camp in Switzerland, have been the subject of extensive archaeological studies. Knowledge of the building time plays a role in reconstructions of the history of this site. We radiocarbon dated mortar samples selected from one of the Roman monuments (Westtor) as well as a nearby Medieval monastery. 14C ages obtained on the first fraction and second fraction of very short dissolution appear close to the expected Roman age of ~2000 BP, while the monastery is dated to historic times, after AD 1308. © 2012 by the Arizona Board of Regents on behalf of the University of Arizona.
Since 1994, our team has gained extensive experience applying accelerator mass spectrometry (AMS) radiocarbon analysis for mortar dating, totaling over 465 samples and 1800+ measured CO2 fractions. Several samples have been analyzed repeatedly. The research covers both Medieval and Classical archaeology. We therefore believe our experience can be helpful when developing preparation procedures for different kinds of mortars in different areas and in varying chronologies. So far, the main areas of interest have been (a) the churches of the Åland Islands (in the archipelago between Finland and Sweden); (b) the churches in the Åboland Archipelago (SW Finland); (c) sites in the Iberian Peninsula including Torre de Palma (a Roman village in Portugal); and (d) Rome, Pompeii, and Herculaneum (Italy). Most of the analyses before 2000 were hydrolized in only two CO2 fractions per sample, and reliability criteria were defined on the basis of how well the ages of the two fractions agree with each other. These criteria have proved most helpful in determining the reliability of ¹⁴C mortar analyses. Different types of mortar have been investigated, including lime mortars made both from limestone and marble, pozzolana mortars, fire-damaged mortars, and mortars based on burnt shells. Most importantly, separate lime lumps sampled from these mortars have been analyzed sporadically and recently more systematically. The research also includes different types of hydrolysis applied in the pretreatment. In addition to using 85% phosphoric acid (H3PO4), the experimental research includes tests with smaller concentrations of phosphoric acid, and tests based on 2–3% hydrochloric acid (HCl) dissolutions. To characterize the dissolution process, results are presented as age profiles of 2–5 CO2 fractions. In our experience, pozzolana mortars have been difficult to date, and HCl dissolution should be used only in special cases and in complementary tests.
DOI: 10.2458/56.17469
This article presents accelerator mass spectrometry (AMS) radiocarbon dates of organic inclusions of cement materials from the House XVII-XVIII Complex located in the Umm el-Jimal archaeological site, east Jordan, aiming at refining the unclear chronology of the house. Fine straws and small fragments of charcoal uncovered from preserved architectural lime mortars and plasters were dated without carrying out extensive excavations. The results indicate that the house most probably was initially plastered or built during the middle of the Byzantine period. The results agree with the historical and archaeological data indicating that Umm el-Jimal flourished during this period; therefore, it is probable that the house was established during this time to meet the housing demand for the increased number of its population.
The morphology of calcium carbonate crystals has been studied at 20ºC during accelerated carbonation using 20% and 100 % volume CO 2 concentrations at ~95% R.H. for lime pastes. Accelerated carbonation resulted in precipitation of calcite crystals with a habit and morphology similar on the sample surface but different along the sample thickness, depending on the lime type and CO 2 concentration. Micrometer-sized rhombohedral calcite crystals precipitated on the sample surface in 100% CO 2 atmosphere while the crystals were sub-micrometer-sized rhombohedral in the 20% CO 2 atmosphere. Through the sample thickness, the carbonated profile was composed of scalenohedral calcite crystals with cracked/corroded surfaces that were disintegrated into nanometer-sized rhombohedra. It has been found that scalenohedral calcite undergoes a significant modification to rhombohedral when exposed to high CO 2 concentrations. This can be explained with a dissolution-reprecipitation process under excess CO 3 2-ions, leading to re-precipitation of nanometer-sized rhombohedral calcite crystals. Despite high CO 2 concentrations, carbonation was not complete due to the heat released during carbonation and precipitated calcite crystals hindering the diffusion of CO 2 .
The Balearic quicklime burials of the Iron Age have been radiocarbon dated. Because the bones found are unsuitable for dating, lime was dated using the titration method, with results indicating that in some samples there is still fossil limestone carbonate present, while other samples suffered from recarbonation. Nevertheless, 14C dates on lime and organic matter agree when both are present. The titration method allows calculating a consensus value. © 2011 by the Arizona Board of Regents on behalf of the University of Arizona.
A number of studies carried out over the last forty years describe the application of radiocarbon dating of lime mixtures such as mortars, plasters and renders. Despite the fact that this method is very simple in principle, several studies have highlighted various practical challenges and factors that must be considered. These arise mainly from the contamination of samples with carbonaceous substances such as incompletely burnt limestone and aggregates of fossil origin including limestone sand.
However, recently studies have shown that accurate sample processing allow a significant reduction of these error sources and moreover adoption of a special sampling procedure based on the careful selection of lumps of incompletely mixed lime, provides an interesting alternative that avoids problems associated with contamination. The founding principle underlying this technique is the use of the pure lime lumps. These are thought to originate from imperfect mixing and are most prevalent in mortars, renders and plasters predating mechanical mixing. Previous sampling methods for radiocarbon dating did not discriminate between pure and contaminated lime lumps. As pure lumps contain the same lime as that used in other parts of the mixtures but importantly are free of contaminants such as sand grains or under burned pieces of limestone, they can dramatically reduce the errors in the radiocarbon dating.
The IntCal09 and Marine09 radiocarbon calibration curves have been revised utilizing newly available and updated data sets from 14C measurements on tree rings, plant macrofossils, speleothems, corals, and foraminifera. The calibration curves were derived from the data using the random walk model (RWM) used to generate IntCal09 and Marine09, which has been revised to account for additional uncertainties and error structures. The new curves were ratified at the 21st International Radiocarbon conference in July 2012 and are available as Supplemental Material at www.radiocarbon.org. The database can be accessed at http://intcal.qub.ac.uk/intcal13/. © 2013 by the Arizona Board of Regents on behalf of the University of Arizona.
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 recrystal- lization 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 parameters— dissolution 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 pro- files and identify CO2 increments that are as uncontaminated as possible. The dating method was implemented on medieval and younger mortars from churches in the Åland Archipelago between Finland and Sweden. The results are used to develop the method for a more general and international use.
The aim of this paper is to explore the full potentialities of Fourier transform infrared (FT-IR) spectroscopy in assessing the chemical and mineralogical composition of ancient pottery, with the final goal of building up a reference databank based on IR spectral transitions. A representative pool of 75 shards excavated in the archaeological district of Canosa (Puglia) was analysed. A detailed attribution of all the spectroscopic frequencies in the spectra recorded in the 4000–400 cm–1 region was attempted and their assignment to different minerals was accomplished, with the support of both literature references and standard materials. In order to demonstrate the reliability of IR attributions, X-ray diffraction analysis was performed on representative samples of the pool. Some information on the firing temperatures, one of the most intriguing aspects in the investigations on ancient pottery, could also be inferred by the FT-IR/XRPD data. The basis is laid for a possible use of IR transitions in assessing the provenance of pottery production.
An error source in radiocarbon dating of ancient mortar is dead carbon of limestone mixed in the matrix. To eliminate the influence of limestone the difference in feasibility to react with acid between mortar and limestone is used. Sin ce the rate of reaction depends on grain size use of a well-defined grain size can give a better separation between mortar and lim e- stone. We present results for the grain size dependence of reaction rates for several mortar and limestone samples and discuss the application for dating.
Abstract: Abstract: Abstract: The presented work shows the methodological problems of mortar radiocarbon dating. Dating of lime mortars is based on setting the present 14C concentration of atmospheric CO2 by mortar carbonates in the hardening process. The big difficulty is the presence of ag- gregate, especially carbonatious one. The application of limestone fragments as aggregate in mortar, is connected with the presence of carbon partially or completely devoid of the radio- active isotope 14C. To carry out radiocarbon dating of the mortars reliably, it was necessary to remove the limestone aggregates. In this context, the application of petrographic studies that enable determination of mineral composition and the percentage of aggregate turns out to be particularly important. Such an identification allows to reconstruct mortar technology and, in combination with geological studies on the investigated terrain, helps to identify the prov- enance of the applied raw material. To make possible the comparison of the analysed mortar results and the verification of the applied methods, in year 2001 control mortars (mortars with established age) were used. The analyses were performed on mortars from a Romanesque castle built in the years 1177-1230 AD (Wleæ, SW part of Poland) and from roman buildings with an approximate age of 140BC-68 AD (west coast of the Dead Sea,). We present the com- plex study of the mortar including both petrographical analyses and radiocarbon dating. The gas proportional counting technique (GPC) was applied for radiocarbon dating. Thin sec- tions of roman mortars showed the carbonatious character of the binder and a large part of the aggregate; this was the source of the apparent age in radiocarbon dating. In spite of ef- forts to eliminate the lime aggregate from the mortar (by freezing, warming up, and separat- ing under the binocular), and taking into consideration the amount of old carbon admixture derived from the carbon stable isotopes composition, there is still a great disproportion be- tween historical and radiocarbon dating of these mortars. The results of the 14C dating show, that improvement of the binder-aggregate separation process is necessary. The mortar aggregate from the Polish castle samples does not contain limestone grits, only scarce quartz grains. These Romanesque mortars were tested successfully and the existing architectural and historical data confirm the results obtained by GPC. K K K
Archaeologists, along with other Quaternary researchers, seldom rely upon a single radiocarbon determination to provide an estimate of the age of the phenomenon which is the object of their study. There is an evident need for an explicitly formulated procedure for comparing sets of radiocarbon determinations from the same and from adjacent strata or sites, and for combining these where statistical and archaeological criteria indicate that this combination is warranted. The present contribution provides explicit modelling for a series of recommended procedures, a critique of previous methods, and paradigms for application of the recommended procedures.
Carbonaceous mortars from Novae (Bulgaria) contain local loess, crushed bricks and ceramic dust (pozzolanic materials). The reaction between lime and pozzolanic additives occurs easily and affects the rate and course of leaching reaction of carbonates in orthophosphoric acid during the sample pretreatment for dating. The composition of the Bulgarian mortars does not allow for unambiguous conclusions about chronology, but together with the observations of experimental mortars, gives new guidelines in terms of pozzolanic mortar application for dating. The presented research illustrates the possible reasons of difficulties with obtaining the appropriate portion of gas for radiocarbon ( ¹⁴ C) measurement. To verify the relative chronology of legionary baths complex in Novae, the charcoals samples were also dated in addition to the mortar.
Radiocarbon ( ¹⁴ C) dating of anthropogenic carbonates (CaCO 3 ) such as ash, lime plaster and lime mortar, has proven a difficult task due to the occurrence of a number of contaminants embedded within the CaCO 3 pyrogenic binder. These include ¹⁴ C-free geologic components and/or secondary phases bearing an unknown amount of ¹⁴ C, and thus the alteration of the original pyrogenic isotopic signature of the material results in major age offsets when carbon recovery is performed through acid hydrolysis. Here we present a characterization/quantification approach to anthropogenic carbonates that includes Fourier transform infrared spectroscopy (FTIR), X-ray diffraction, thin section petrography, thermogravimetric analysis and scanning electron microscopy coupled with high-resolution cathodoluminescence, with which we identified the pyrogenic CaCO 3 fraction in an aerial lime plaster and two hydraulic mortars. The preserved pyrogenic component was then isolated by density separation and its purity checked again using FTIR. Carbon was recovered through thermal decomposition in vacuum. The resulting ¹⁴ C age matches the expected age of the lime plaster, whereas hydraulic mortars are slightly offset due to the carbonation of calcium hydroxide lumps. This approach highlights the importance of a dedicated characterization strategy prior to dating and may be applied to aerial lime plasters to obtain accurate ages.
When sampling mortars for radiocarbon ( ¹⁴ C) dating it is crucial to ensure that the sample has hardened rapidly relative the resolution of the dating method. Soft and porous lime mortars usually fulfill this criterion if the samples are taken from an uncovered surface from less than a few centimeters deep. However, hard, concrete-like mortars may be impermeable for carbon dioxide and even the outermost centimeters may still contain uncarbonated calcium hydroxide. These mortars may harden very slowly and contain carbonate that formed centuries or even millennia after the original building phase, and they can still be alkaline and capture modern ¹⁴ C, causing younger ¹⁴ C ages than the actual construction age. Another problem is reactivation of the binder carbonate if it has been partly decarbonated during a fire later on in its history. It will be shown that these young carbonates dissolve rapidly in phosphoric acid and in many cases a reasonable ¹⁴ C age can be read from ¹⁴ C profiles in sequential dissolution if the measurements from initially formed carbon dioxide are disregarded. However, if a mortar was made waterproof deliberately by adding crushed or ground tile, as in Roman cocciopesto mortars, it may be very difficult to get a conclusive dating.
This paper presents the results of radiocarbon dating of bulk mortars and reports an attempt of implementation of the knowledge about the isotopic fractionation, based on δ13C measurements, to make the age correction for mortars, together with verification of such correction based on the percentage estimation of carbonate components, namely binder and aggregate. To evaluate the variability of isotopic fractionation during CO2 absorption by mortar, dependent on the climatic and environmental conditions, and the type of mortar, the δ13C measurements have been performed for the mortars from Sussita (Golan Heights). Such measurements were also made for fragments of natural carbonate rocks and for mortars produced in the laboratory from the same substrate. We propose the recipe for mortars age estimation.
An accurate radiocarbon ( ¹⁴ C) dating of mortars requires adjusting the sample preparation procedure to each specific mortar composition. In order to follow the influence of mortar components and the preparation procedure on dating results, a mortar intercomparison study (MODIS) was undertaken by 10 organizations (institutes and laboratories) in the analyses of four different types of mortars (see in this issue Hajdas et al. 2017 and Hayen et al. 2017). This paper presents the preparation protocol DoM v.1 applied by the Poznań team, together with dating results on a set of mortar samples used for the of intercomparison. This procedure involved petrographic observations, SEM-EDS analyses, different mechanical-chemical preparation, a test of leaching reaction for available fractions, and finally ¹⁴ C dating of chosen samples. The applied preparation allows one to obtain dry-sieved grain fractions and different fractions from suspension: grain fractions from suspension collected in different times of leaching, repeated suspension (different portions), as well as suspension collected at different times of sedimentation. The obtained results show the great importance of good sampling and the influence of sample preparation on ¹⁴ C dating results.
Absolute dating of mortars is crucial when trying to pin down construction phases of archaeological sites and historic stone buildings to a certain point in time or to confirm, but possibly also challenge, existing chronologies. To evaluate various sample preparation methods for radiocarbon ( ¹⁴ C) dating of mortars as well as to compare different dating methods, i.e. ¹⁴ C and optically stimulated luminescence (OSL), a mortar dating intercomparison study (MODIS) was set up, exploring existing limits and needs for further research. Four mortar samples were selected and distributed among the participating laboratories: one of which was expected not to present any problem related to the sample preparation methodologies for anthropogenic lime extraction, whereas all others addressed specific known sample preparation issues. Data obtained from the various mortar dating approaches are evaluated relative to the historical framework of the mortar samples and any deviation observed is contextualized to the composition and specific mineralogy of the sampled material.
Bayesian models have proved very powerful in analyzing large datasets of radiocarbon ( ¹⁴ C) measurements from specific sites and in regional cultural or political models. These models require the prior for the underlying processes that are being described to be defined, including the distribution of underlying events. Chronological information is also incorporated into Bayesian models used in DNA research, with the use of Skyline plots to show demographic trends. Despite these advances, there remain difficulties in assessing whether data conform to the assumed underlying models, and in dealing with the type of artifacts seen in Sum plots. In addition, existing methods are not applicable for situations where it is not possible to quantify the underlying process, or where sample selection is thought to have filtered the data in a way that masks the original event distribution. In this paper three different approaches are compared: “Sum” distributions, postulated undated events, and kernel density approaches. Their implementation in the OxCal program is described and their suitability for visualizing the results from chronological and geographic analyses considered for cases with and without useful prior information. The conclusion is that kernel density analysis is a powerful method that could be much more widely applied in a wide range of dating applications.
If radiocarbon measurements are to be used at all for chronological purposes, we have to use statistical methods for calibration. The most widely used method of calibration can be seen as a simple application of Bayesian statistics, which uses both the information from the new measurement and information from the 14 C calibration curve. In most dating applications, however, we have larger numbers of 14 C measurements and we wish to relate those to events in the past. Bayesian statistics provides a coherent framework in which such analysis can be performed and is becoming a core element in many 14 C dating projects. This article gives an overview of the main model components used in chronological analysis, their mathematical formulation, and examples of how such analyses can be performed using the latest version of the OxCal software (v4). Many such models can be put together, in a modular fashion, from simple elements, with defined constraints and groupings. In other cases, the commonly used “uniform phase” models might not be appropriate, and ramped, exponential, or normal distributions of events might be more useful. When considering analyses of these kinds, it is useful to be able run simulations on synthetic data. Methods for performing such tests are discussed here along with other methods of diagnosing possible problems with statistical models of this kind.
I have developed a method of dating early medieval Irish buildings using charcoal encased in mortar. Due to the inclement weather over centuries, timbers do not preserve well in these structures, leaving little suitable material for 14 C dating. Initially, several buildings of known age were analyzed to verify the mortar charcoal technique. Then, a series of buildings for which no definite architectural-historical dates existed, e.g., churches, houses, oratories and round towers, was successfully tested. I discuss here the results of this dating approach, and provide architectural historians with a firmer understanding of the origin and antiquity of early Irish buildings.
The presented research involves the analysis and radiocarbon dating of 2 different groups of carbonate mortars, from Kraków, Poland and Hippos, Israel. Differences in composition of the mortars are reflected in different rates of their acid leaching. The Israeli mortars contain carbonate-basaltic aggregates, which may cause overestimation of 14́C age. Preliminary processing of these samples (choice of selected grain-size fraction and collection of CO2 released during the first phase of the acid-leaching reaction), enabled us to obtain good agreement between the 14C dates and the age derived from historical contexts. A similar method of preliminary processing was applied to the carbonate mortars of the Medieval building in Kraków. The Polish samples represent carbonate mortars with some admixture of quartz aggregates, suggesting that they would be an ideal material for 14C dating. However, these samples contained white lumps of carbonates, the structure of which differed from that of the binder. These admixtures, possibly related to the hydrological conditions at the site and to the character of the ingredients, appeared modem, and if not removed prior to acid leaching, they could cause underestimation of the age of samples. The 14C dates of the mortars from the walls of the Small Scales building in Kraków are the first obtained for this object, and their sequence does not contradict archaeological indications on several phases of the building construction. © 2009 by the Arizona Board of Regents on behalf of the University of Arizona.
Radiocarbon dating was first applied to historic lime mortars during the 1960s. However, despite the relative simplicity of the technique in principle, a number of subsequent studies have highlighted important aspects that should be considered. One of the most significant of these challenges arises from sample contamination by carbonaceous substances such as incompletely burnt limestone and aggregates of fossil origin containing "dead" 14C. More recent studies have shown that in the majority of old lime-based mixtures the contamination problem can be avoided through selection of pure lime lumps. These particular types of lumps are believed to originate from areas where the lime is incompletely mixed with the aggregate. It has been demonstrated that even a single lime lump can provide sufficient material for a 14C date of the mortar from which the lump was taken (Pesce et al. 2009). This paper describes the practical challenges associated with location, extraction, and preparation of 4 lime lumps extracted from 2 new sites for 14C dating. These include distinguishing the lime lumps from other lumps present in the matrix and the removal of material surrounding the lime lump. The coherence of 14C dating with other archaeological information on the chronology of historic sites is highlighted through case studies. © 2012 by the Arizona Board of Regents on behalf of the University of Arizona.
This research is aimed at radiocarbon dating organic inclusions and lime-binder powders of mortar layers of mosaic pavements in four churches of arguable archaeological date located in northern Jordan. One mortar sample from each mosaic pavement of each church was collected, examined by thin section microscopy, and then physically pretreated by gentle crushing and dry sieving to collect lime-binder powders of different grain sizes. Charcoal samples uncovered from three samples and the CO2 gases, collected by hydrochloric acid (HCl) hydrolysis of the powders, were 14C dated using accelerator mass spectrometry (AMS). Four powders of 63–45 μm from the four samples and two powders of 45–38 μm from two samples were analyzed in order to get more precise dates and examine previous proposed models for the interpretation of the results. 14C determinations showed agreement between charcoal ages and archaeological data, while the fine lime-binder’s powders, especially from the mosaic’s bedding layer, produced more precise dates. Results suggest that 14C date profiles produced by HCl hydrolysis of the lime-binder powders can be clearly interpreted by the existing models. © 2015 by the Arizona Board of Regents on behalf of the University of Arizona.
Lime mortars as a mixture of binder and aggregate may contain carbon of various origins. If the mortars are made of totally burnt lime, radiocarbon dating of binder yields the real age of building construction. The presence of carbonaceous aggregate has a significant influence on the 14C measurements results and depending on the type of aggregate and fraction they may cause overaging. Another problem, especially in case of hydraulic mortars that continue to be chemically active for a very long time, is the recrystallization usually connected with rejuvenation of the results but also, depending on local geological structures, with so called reservoir effect yielding apparent ages.
Lime mortar can be dated successfully by the following important modifications in technique: 1) crushing and sieving to remove inert aggregate; 2) acidization of live mortar and taking only the first fraction of gas evolved, that fraction which has least contamination; 3) correction of results by δ C13 and dendrochronology. We have applied this technique to buildings in Stobi with generally successful results.
Radiocarbon dating has had an enormous impact on archaeology. Most of the dates are obtained using charred materials and, to a lesser extent, collagen from bones. The contexts in which charred materials and bones are found are often, however, not secure. There are 3 other datable materials that are usually in secure contexts: plaster/mortar, phytoliths, and the organic material in the ceramic of whole vessels. The plaster/mortar of walls and floors are often in very secure contexts. Phy-toliths are abundant in archaeological sites and in some situations form well-defined surfaces. Whole vessels are usually found in secure contexts and their typologies are indicative of a specific period. Dating each of these materials has proved to be difficult, and solving these technical problems represents major future challenges for the 14 C community. The effective use of charcoal and bone collagen for dating can also be improved by paying careful attention to the micro-contexts in which they are found, such as in clusters or as part of well-defined features. Pre-screening to identify the best preserved material can also contribute to improving the accuracy of the dates obtained. A general objective should be to have an assessment of the quality of the material to be dated so that the potentially invaluable information from outliers can be exploited.
The present work describes the methods for detecting and classifying calcite in archeological ceramics, the forms of calcite and their interpretation in archeometric terms. Calcite appears in form of coarse granules and fine particles, and its origin can be primary or secondary. Coarse granules can be polycrystalline or mono-crystals of calcite. Fragments of shells, fossils or microfossils are also found. Primary calcite is the initial calcite preserved in low-fired pottery. Secondary calcite, formed after the ceramic firing, may be reformed (re-carbonated) calcite, precipitated calcite or calcite from alteration. The firing can cause the formation of a ‘reaction rim’ around coarse granules of calcite, while strong decomposition of coarse calcite causes the formation of ‘calcite ghosts’. The identification of the forms of calcite gives information on raw materials, the firing temperature and the manufacturing technology of the pottery.
The results of a masonry analysis of the majority of Irish pre-Romanesque church- es are presented. A number of local styles are identified in high-density areas, most- ly in the west of the country and it is shown that the differences between these styles were not determined by geology. It is argued that these styles represent habitual variation and are therefore indicative of local groups of masons working over a rel- atively short period of time. This assessment is supported by an analysis of stone supply that suggests that quarrying was organised in an ad hoc manner to supply local needs. These churches are normally placed within a broad timeframe span- ning the tenth to early-twelfth centuries but a number of factors combine to suggest that the habitual styles are a relatively late development, perhaps mainly from the mid-eleventh century onwards. Some of the implications of this proposed refine- ment of the existing chronology are briefly discussed.
In the production of lime mortars CaCO3 is converted to CaO. Upon setting the CaO reacts with atmospheric CO2 to form CaCO3. Attempts to date mortars based on the carbon content of the CaCO3 have been hampered by two major factors. The original CaCO3 may not have been completely converted to CaO during heating and the sample will then contain dead carbon leading to an incorrect date. Secondly, marble chips from a construction site may have been added as part of the aggregate material. This will also add dead carbon and produce an erroneous date. The lime mortars contain a second possible source of carbon for dating. Small fragments of charcoal and plant material are often found upon crushing of the sample. This material can be used as the source of carbon for dating. Potential sources of dead carbon in this part of the sample would be if coal was used in the heating process. The use of AMS to determine 14C in lime mortars significantly reduces the amount of sample required and allows measurements to be made on standing structures. The comparison of 14C in lime mortars should allow original and reconstructed or repaired areas of architecturally and historically significant buildings to be discerned. An attempt to apply this method is being made at Pontigny Abbey, a Cistercian church in northern Burgundy which has been dated approximately to the mid-12th century. The building has flying buttresses which appear to belong to the original building campaign, although this structural support is not presently believed to have been developed until several decades later. Conventional art historical methods have been unable to determine whether the flying buttresses are original or added. Recent examinations point to the possibility that they are part of the original structure. Measurements of the 14C content of the plant material found in the lime mortars of the flying buttresses, the earliest parts of the building, and known reconstructed areas of the abbey were attempted.
Carbon dioxide trapped in mortars during preparation yields C/sup 14/
that may be used for dating. Four samples from buildings of known ages were
measured by this method, and the hypothesis was verified. Preliminary
microscopic examinations are necessary to reveal Foraminifera that might add
unknown quantities of ancient carbonates. (H.M.G.)
This research investigates plaster and mortar samples from different structures at Petra, Southern Jordan. It aims at radiocarbon dating organic inclusions uncovered from these samples in order to refine the chronology of the structures sampled. One of the structures has a Latin inscription so it was used to crossdate its radiocarbon date. The radiocarbon dates of most of the samples synchronize the archaeological records and dates of the structures.
This paper describes a method for effective separation of the pure binder fraction of lime mortars for reliable radiocarbon dating. The methodology allows removal of the detrital carbonate fraction and the unburnt limestone particles, obtaining particles of under 1 μm. The extracted fraction ensured that all carbonate has been generated by slaked lime carbonation. Consequently, the measured carbon corresponds to atmospheric carbon. The proposed method allows to obtain pure datable binder, simplifying considerably the performance of radiometric measurements because dating other grain-size fraction is unnecessary. In order to prove the effectiveness of binder refining, the extraction method has been applied to 5 lime mortars of different archaeological periods from the perimeter walls of Santa María la Real parish church (Zarautz, northern Spain). © 2012 by the Arizona Board of Regents on behalf of the University of Arizona.
Centre for Isotopic Research on Cultural and Environmental heritage (CIRCE) has, recently, obtained some promising results in testing the feasibility of mortar radiocarbon dating by means of an ad hoc developed purification procedure (CryoSoniC: Cryobraking, Sonication, Centrifugation) applied to a series of laboratory mortars. Observed results encouraged CryoSoniC accuracy evaluation on genuine mortars sampled from archeological sites of known or independently constrained age (i.e., other 14C dates on different materials).In this study, some 14C measurements performed on genuine mortars will be discussed and compared with independently estimated (i.e., radiocarbon/archaeometrical dating) absolute chronologies of two Spanish sites. Observed results confirm the agreement of the CryoSoniC mortar dates with the archaeological expectations for both examined cases.Several authors reported the possibility of obtaining accurate radiocarbon dates of mortar matrices by analyzing lime lumps: binder-related particles of different sizes exclusively composed of calcium carbonate.In this paper, preliminary data for the absolute chronology reconstruction of the Basilica of the cemetery complex of Ponte della Lama (Canosa di Puglia, Italy) based on lime lumps will also be discussed. Dating accuracy will be quantified by comparing 14C data on mortar lime lumps from a funerary inscription of known age found near the Basilica, in the same study site. For this site, a comparison between absolute chronologies performed by bulk and CryoSoniC purified lime lumps, and charcoal incased in mortars (when found) will also be discussed.Observed results for this site provide evidence of how bulk lime lump dating may introduce systematic overestimations of the analyzed sample while CryoSoniC purification allows accurate dating.
Infrared spectrometry is a well-established method for the identification of minerals. Due to its simplicity and the short time required to obtain a result, it can be practiced on-site during excavation using portable infrared spectrometers. However, the identification of a mineral may not be sufficient. For example, a lime plaster floor and a crushed chalk surface have a similar appearance and are composed of the same mineral – calcite. Here we exploit differences in the infrared spectra of geogenic, biogenic and pyrogenic calcites for the identification of each calcite type. The infrared calcite spectrum has three characteristic peaks in the region of 400–4000 cm−1, designated ν2, ν3, and ν4. When a calcite sample is ground, as part of the measurement preparation procedure, some grinding dependent changes will be revealed in the infrared spectrum. With additional grinding, the ν3 peak narrows and the heights of the ν2 and ν4 peaks decrease, when both are normalized to the ν3 height. By plotting the normalized heights of the ν2versus the ν4 of several grindings of the same sample, a characteristic trend line is formed for each calcite type. The trend lines of geogenic calcites have the shallowest slopes and highest ν4 values when compared to pyrogenic calcites, which can be further divided to ash and plaster/mortar samples. This method can assist in distinguishing between the various calcites, and provide insights into homogeneity and preservation state of the calcitic materials in question. Also available in Memorial University Research Repository at http://research.library.mun.ca/6251/