Acid-base-acid Research Articles

To pretreat, or not to pretreat, that is the question. The value of pretreatment protocols in the stable carbon and nitrogen isotope analysis of archaeobotanical cereal grains from Croatia and Serbia

ABSTRACT Isotopic analysis of archaeological charred plant remains is a useful tool to infer past agricultural practices. However, debate continues over whether charred seeds should be untreated or pretreated before analysis, to counteract any residual contamination and retrieve the “true” isotopic signature of the seed. This paper presents a case study examining whether archaeobotanical remains from Croatia and northern Serbia should be pretreated before isotopic analysis with the aim to provide a pragmatic technique for wider application. A small subset was first examined with an ATR-FTIR and then four different protocols were examined: water rinse only, two different acid-only methods and ABA (acid–base-acid). The results were inconsistent, displaying variability in the effect each protocol had on the isotopic values. Overall, it was concluded that the slight differences between untreated and pretreated sub-samples should not impact the archaeological interpretation, removing the need for pretreatment of the remaining archaeobotanical material.

THE INFLUENCE OF PLANT SPECIES AND PRETREATMENT ON THE 14C AGE OF CAREX-DOMINATED PEAT PLANTS OF A PEAT CORE FROM JINCHUAN MIRE, NE CHINA

ABSTRACT The comparisons among 126 14C dates of Carex samples including separated leaf and root parts with acid (A)-treatment and acid-base-acid (ABA)-treatment, and 48 published 14C dates of bulk peat plants on a 92-cm core from Jinchuan Mire in NE China, indicate old carbon influence (OCI) on the 14C dates. The OCI varies with plant species, pretreatment and peat depth. In vascular peat plants such as Carex, humin fractions (remains after ABA treatment) and humic acids are representative of the original plant precursor, while fulvic acids are regarded as the secondary mobile product which should be removed for 14C dating. ABA- treatment removes both fulvic acids and humic acids, whereas A-treatment gets rid of only fulvic acids. Carex roots uptake more dissolved CO2 in peat water. Carex leaves may use more CO2 (involving degassing CO2) above the peat surface. By removing humic acids throughout ABA treatment, the OCI may vary differently over depth (time). ABA treatment cannot eliminate the fixed OCI in humin fractions of vascular peat plants, instead, this treatment may enhance OCI by removing humic acid which may represent the true age of the plants. In addition, Bacon model results on this core could not show rapid changes in accumulation rate.

Radiocarbon and luminescence dating of the Wulanmulun site in Ordos, and its implication for the chronology of Paleolithic sites in China

After the Salawusu and Shuidonggou sites, the Wulanmulun site found in 2011 is another important Paleolithic site in Ordos, China, due to its numerous stone artifacts and animal fossils. Here, we carry out a combined luminescence and radiocarbon dating of the site. The luminescence dating was done on coarse-grained quartz from 24 sediment samples using a single-aliquot regenerative-dose (SAR) protocol. The radiocarbon dating was performed on ten charcoal samples and one bone sample using acid-base-acid (ABA) and acid–base-wet oxidation-stepped combustion (ABOx-SC) pretreatments. The results showed that: (i) although some samples show relative large (>20%) overdispersion in De distribution (small aliquots), the quartz grains are considered to be sufficiently bleached before burial; (ii) the quartz OSL ages of ∼4–65 ka obtained for the samples are generally stratigraphically consistent and reliable; (iii) the radiocarbon ages obtained using the ABA pretreatment procedure are much younger than the corresponding OSL ages, and the radiocarbon ages obtained using the ABOx-SC method are beyond or close to the laboratory background. The radiocarbon ages obtained using the ABA treatment were considered to be underestimated. This implication is that caution must be taken for dating Chinese Paleolithic (>25 ka) using the ABA pretreatment procedure on carbon samples. Finally, the cultural layers from the Wulanmulun site are deduced to be between 50 and 65 ka. • Wulanmulun is a newly excavated Paleolithic site in Ordos in north China. • A total of 24 sediment samples were luminescence dated using the SAR protocol on quartz grains. • Ten charcoal and bone samples were radiocarbon dated using different pretreatment procedures. • The radiocarbon ages are underestimated when using the acid-base-acid pretreatment. • The cultural layers of the site are dated to 65–50 ka.

A radiocarbon chronology for Sanamere Lagoon, Cape York Peninsula, using multiple organic fractions

The selection and pre-treatment of reliable organic fractions for radiocarbon age determination is fundamental to the development of accurate chronologies. Sampling from tropical lakes is particularly challenging given the adverse preservation conditions and diagenesis in these environments. Our research is the first to examine and quantify the differences between radiocarbon ages from different carbon fractions and pretreatment protocols from tropical lake sediments. Six different organic fractions (bulk organics, pollen concentrate, cellulose, stable polycyclic aromatic carbon (SPAC), macrocharcoal >250 μm and microcharcoal >63 μm) were compared at six different depths along a 1.72 m long core extracted from Sanamere Lagoon, Cape York Peninsula, northern Australia. Acid-base-acid (ABA), modified ABA (30% hydrogen peroxide + ABA), 2chlorOx (a novel cellulose pre-treatment method) and hydrogen pyrolysis (hypy) were used to pre-treat the organic fractions. The oldest date is ∼31,300 calibrated years before present (cal yr BP) and the youngest is ∼2800 cal yr BP, spanning ∼28,500 years. The smallest offset between the minimum and the maximum age for different fractions and across pretreatment methods at a given depth was found to be 832 years (between SPAC and pollen) and the largest ∼16,750 years (between pollen concentrate and SPAC). The SPAC fractions pre-treated with hypy yielded older ages compared to all other fractions in most cases, while bulk organics yielded consistently younger ages. The magnitude and consistency of the offsets and the physical and chemical properties of the tested organic fractions suggest that SPAC is the most reliable fraction to date in tropical lake sediments and that hypy successfully removes exogenous carbon contamination. • Stable polycyclic aromatic carbon is the most reliable fraction to date tropical lake sediments. • Hydrogen pyrolysis (hypy) successfully removes contamination sourced from exogenous carbon. • The age-depth model from the peroxide+ABA pretreated bulk organics samples agrees with the hypy pretreated samples.

SUITABILITY OF ACID-SOLUBLE AND ACID-INSOLUBLE LEATHER FRACTIONS IN RADIOCARBON DATING

ABSTRACTLeather has been produced by a variety of methods throughout human history, providing researchers unique insight into multiple facets of social and economic life in the past. Archaeologically recovered leather is often fragile and poorly preserved, leading to the use of various conservation and restoration efforts that may include the application of fats, oils, or waxes. Such additives introduce exogenous carbon to the leather, contaminating the specimen. These contaminants, in addition to those accumulated during interment, must be removed through chemical pretreatment prior to radiocarbon (14C) dating to ensure accurate dating. DirectAMS utilizes organic solvents, acid-base-acid (ABA) and gelatinization for all leather samples. Collagen yield from leather samples is variable due to the method of production and the quality of preservation. However, evaluating the acid-soluble collagen fraction, when available, provides the most accurate 14C dates for leather samples. In instances where gelatinization does not yield sufficient material, the resulting acid-insoluble fraction may be dated. Here we examine the effectiveness of the combined organic solvent and ABA pretreatment with gelatinization for leather samples, as well as the suitability of the acid-insoluble fraction for 14C dating.

AMS 14C DATING OF THE MAYAN CODEX OF MEXICO REVISITED

ABSTRACTThe Mayan Codex of Mexico (MCM), the only Mayan codex found in the 20th century, was unveiled in 1971 during the Ancient Maya Calligraphy exhibition at Club Grolier. The codex comprises 10 pages of bark paper in accordion format, coated with a layer of plaster on both sides. It illustrates the synodic cycles of Venus, with its four phases. Since its discovery, the MCM has been subject to controversy and discussions about its authenticity. In 2016, a group of specialists led by Baltazar Brito chief of the National Library of Anthropology and History, carried out an exhaustive study of the codex with the purpose of determining its temporality and authenticity. In this work, the pre-Columbian authenticity of the codex is verified by the radiocarbon (14C) technique using AMS. Two cleaning procedures were contrasted: the standard acid-base-acid (ABA) protocol and a second one with Soxhlet plus ABA. Results obtained when samples were prepared following ABA protocol only, placed the age of the bark paper between 991 and 1147 cal AD. The second cleaning method with Soxhlet plus ABA, resulted in younger ages, between 1159 and 1261 cal AD. However, we consider that when Sohxlet is used as part of the cleaning protocol, organic contaminants are reduced to a minimum, and 14C dates are more reliable. These results indicate that the vegetal support of the MCM belongs to Postclassical Mayan period and place it as the oldest known manuscript of America found to date.

PREPARATION OF WOOD, CHARCOAL AND BONE COLLAGEN MICRO SAMPLES USING AUTOMAT FOR AMS RADIOCARBON DATING.

For the pretreatment of wood, charcoal and collagen from bone micro samples using the Acid-Base-Acid (ABA) method, we have assembled an automated computer-controlled unit in our laboratory CRL. The sample is placed in a glass single-necked cuvette. The machine consists of prepared solutions which are guided through capillaries, switching valve and peristaltic pump into the cuvette with the sample according to the currently selected program. The automat can be used for the pretreatment of charcoal, wood and also collagen from bones.

Study of Jinchuan Mire in NE China I: AMS 14C, 210Pb and 137Cs dating on peat cores

This paper presents dating results of AMS 14C, 210Pb and 137Cs methods on two young peat profiles from Jinchuan Mire in southeast Jilin of China. JC1 (50-cm long) from a hummock of the mire covers 1962–2007 CE with an accumulation rate of 1.12 cm/y, whereas JCA (92-cm long) from a lawn site involves a 1000-year record with a mean sedimentation of 0.09 cm/y. Comparison of the dating results of the last 100-y part of the peat cores, chronologies based on the AMS 14C dating are most reliable, because the mobility of 210Pb and 137Cs in peat profiles causes overestimation of depositional rate with the larger errors in the deeper layers. The F14C of peat samples were significantly lower than that of the atmospheric CO2 for the post nuclear bomb period because of three reasons: (1) uptake of old CO2 dissolved in the water by aquatic plants during photosynthesis; (2) long-term mixing of the atmospheric CO2 in multiple year growth of the plants; and (3) perhaps dilution effect caused by strong surface runoff. Among these factors, Factor (1) accounts for the major influence. Hence, a “bomb 14C curve” from a peat profile is necessary for determining post bomb ages. For the pre-nuclear bomb ages, acid-base-acid (ABA) treatment of a peat sample may cause an older-than-true age due to removal of organic acids produced during photosynthesis. This observation calls for detailed investigation of mechanism study and proper pretreatment of peat samples for 14C dating. The large difference of the depositional rates in the same peatland between JC1 and JCA indicates that estimation of carbon storage in a peatland should be based on the database of multiple sites rather than a couple of cores. For the same reason, one should not use a depositional rate either from a core with distance in the same peatland or from an adjacent peatland.

High-Resolution Peat Core Chronology Covering the Last 12 KYR Applying an Improved Peat Bog Sampling

ABSTRACTThis work focuses on building a high-resolution age-depth model for quantitative palaeoclimate study from the Mohos peat bog, East Carpathian mountains. The investigated core presents a continuous peat profile for the last 12 kyr. The chronology was based on 36 accelerator mass spectrometry radiocarbon (AMS14C) analyses of the separatedSphagnumsamples from different depths of the profile. DrySphagnumsamples for AMS dating were prepared using the classic acid-base-acid (ABA) method followed with an oxidative bleaching step to get clean cellulose.Sphagnumcellulose samples were measured by AMS using the EnvironMICADAS at the ICER (Debrecen, Hungary). A high-resolution chronology was obtained with the use of Bayesian age-depth modeling. Peat accumulation rate has been calculated and the sections with variable accumulation rate values were observed along the profile.

Molecular characterization of charcoal to identify adsorbed SOM and assess the effectiveness of common SOM-removing pretreatments prior to radiocarbon dating

Abstract A significant part of our knowledge on Holocene landscape development and associated human history in northwestern Europe is based on radiocarbon dating of charcoal originating from podzols. However, these soils are characterized by leaching of soil organic matter (SOM) that may adsorb to older charcoal, resulting in incorrect charcoal radiocarbon ages. Several pretreatments, such as an acid-base-acid (ABA) sequence for Holocene-aged samples and a harsher acid-base-oxidation (ABOx) sequence for older samples, have been developed to remove the adsorbed fractions. While commonly used, evidence for the effectiveness of these pretreatments thus far has been circumstantial, by assessing the impact of these pretreatments on the radiocarbon age. In this study, we performed a direct molecular assessment of the presence, adsorption, and removal of SOM-compounds by pyrolysis-GC-MS based characterization of charcoal fragments and SOM obtained from a podzol located in the Laarder Wasmeren area, the Netherlands. In addition, the removal efficiency of adsorbed SOM by four different pretreatments was analysed. Molecular evidence for significant adsorption of SOM was found and the four pretreatments showed different efficiencies in removal thereof as evidenced by the residual charcoal composition. ABOx resulted in the most simplified Py-GC-MS chromatogram and thus comes closest to the isolation of recalcitrant carbon. The most recalcitrant organic fraction is likely to have the best interpretable age, since the highest decontamination can be expected for this fraction. Hence, it is advisable to use ABOx as standard pretreatment for the removal of adsorbed SOM fractions from charcoal, provided that the sample size is large enough.

AMS 14C dating of the hominin archaeological site Chuandong Cave in Guizhou Province, southwestern China

This study presents detailed AMS 14C dating of charcoals, burned and unburned bones, and teeth from the hominin archaeological site Chuandong Cave, located in Puding County, Guizhou Province, southwestern China. The charcoal samples were pretreated with either the acid−base−acid (ABA) or ORAU−XR method, the unburned bone and teeth samples with ABA-collagen pretreatment, and the burned bone samples with the ORAU−CB method. The AMS 14C ages of the charcoal samples provide the most reliable results in this study. The AMS 14C dates of the bone samples are generally younger, possibly due to posterior amino acid contamination. Based on the AMS 14C ages, we propose the following chronology for the site: Layers 3 to 5 formed between 11.5–12.5 ka BP (all 14C ages reported in this study are calibrated ages unless stated otherwise. A BP = years before 1950 CE), a period corresponding to the Younger Dryas; Layers 6 to 7 formed between 14–24 ka BP, a period including the Last Glacial Maximum (LGM); and Layers 8–9 likely formed before 34 ka BP corresponding to the late Pleistocene. According to the above chronology, the Chuandong humans (modern Homo sapiens) were present at 12 ka BP, i.e., the late Pleistocene. This conclusion differs from the previous estimate at ∼9 ka BP, i.e., the early Holocene. Furthermore, the Chuandong Culture likely began as early as 34 ka BP and survived in the region throughout the cold and dry LGM. Detailed studies on the hominin archaeological sites in Guizhou, including Chuandong Cave and Maomaodong Cave, are warranted to better understand hominin evolution in Asia.

Evaluation of Preparation Methods in Radiocarbon Dating of Old Wood

AbstractFrom the early days of radiocarbon dating, the standard sample treatment has involved removal of contamination from carbonates and humic acids by washes in acid and base, respectively. A modification of this acid-base-acid (ABA) method has been suggested, especially for material older than 20,000 yr. However, the criticism of ABA and application of a more aggressive oxidizing method, such as wet oxidation (ABOX) or cellulose extraction, might only be needed in some special cases, for example, in the case of poorly preserved or chemically treated wood. Separation of cellulose seems to be the ultimate solution; however, it is not always applicable when samples contain small amounts of wood. As a part of studies focusing on the chronology of late Pleistocene sedimentary processes in the Venetian–Friulian Plain and Carnic Alps (NE Italy), 14C analyses were performed on old wood samples found in sedimentary deposits of pre-Last Glacial Maximum (LGM) age. Wood samples were treated by five methods: ABA, two modified ABA treatments (ABOX and ABA+Bleach), as well as two different cellulose separations. Infrared spectra of treated samples and 14C results show that in most cases the ABA method is sufficient in removing the contamination of naturally deposited wood, even when the wood is of very old age.

Towards an Accurate and Precise Chronology for the Colonization of Australia: The Example of Riwi, Kimberley, Western Australia.

An extensive series of 44 radiocarbon (14C) and 37 optically stimulated luminescence (OSL) ages have been obtained from the site of Riwi, south central Kimberley (NW Australia). As one of the earliest known Pleistocene sites in Australia, with archaeologically sterile sediment beneath deposits containing occupation, the chronology of the site is important in renewed debates surrounding the colonization of Sahul. Charcoal is preserved throughout the sequence and within multiple discrete hearth features. Prior to 14C dating, charcoal has been pretreated with both acid-base-acid (ABA) and acid base oxidation-stepped combustion (ABOx-SC) methods at multiple laboratories. Ages are consistent between laboratories and also between the two pretreatment methods, suggesting that contamination is easily removed from charcoal at Riwi and the Pleistocene ages are likely to be accurate. Whilst some charcoal samples recovered from outside hearth features are identified as outliers within a Bayesian model, all ages on charcoal within hearth features are consistent with stratigraphy. OSL dating has been undertaken using single quartz grains from the sandy matrix. The majority of samples show De distributions that are well-bleached but that also include evidence for mixing as a result of post-depositional bioturbation of the sediment. The results of the two techniques are compared and evaluated within a Bayesian model. Consistency between the two methods is good, and we demonstrate human occupation at this site from 46.4–44.6 cal kBP (95.4% probability range). Importantly, the lowest archaeological horizon at Riwi is underlain by sterile sediments which have been dated by OSL making it possible to demonstrate the absence of human occupation for between 0.9–5.2 ka (68.2% probability range) prior to occupation.

Successfully Dating Rock Art in Southern Africa Using Improved Sampling Methods and New Characterization and Pretreatment Protocols

AbstractWorldwide, dating rock art is difficult to achieve because of the frequent lack of datable material and the difficulty of removing contamination from samples. Our research aimed to select the paints that would be the most likely to be successfully radiocarbon dated and to estimate the quantity of paint needed depending on the nature of the paint and the weathering and alteration products associated with it. To achieve this aim, a two-step sampling strategy, coupled with a multi-instrument characterization (including SEM-EDS, Raman spectroscopy, and FTIR spectroscopy analysis) and a modified acid-base-acid (ABA) pretreatment, was created. In total, 41 samples were dated from 14 sites in three separate regions of southern Africa. These novel protocols ensure that the14C chronology produced was robust and could also be subsequently applied to different regions with possible variations in paint preparation, geology, weathering conditions, and contaminants.

Evaluation of Sample Preparation Protocols for the 14C Dating of Tupiguarani Pottery in Southeastern Brazil

AbstractThis study evaluates the radiocarbon dating of ceramic samples from Tupiguarani sites in Brazil, a settlement type dating up to 3000 cal BP. In this work, residues from ceramic samples from four archaeological sites in Rio de Janeiro (Morro Grande, Serrano, Barba Couto, and Bananeiras) were analyzed. In order to identify the most suitable sample preparation protocols, the humic fraction was isolated from the bulk material at the Oxford Radiocarbon Accelerator Unit (ORAU), whereas the acid-base-acid (ABA) residue fraction method was applied at the Radiocarbon Laboratory of the Fluminense Federal University (LAC-UFF). The dating results were compared to the current knowledge about the occupational periods of the sites. For the Morro Grande site, the results of humic and ABA residue fractions show a difference of more than 1500 yr. For the Serrano site, the 14C ages obtained from the two pretreatments are identical, and as with the Barba Couto and Bananeiras sites, indicate an occupation during the Brazilian colonial period of the 16th century AD and are compatible with the archaeological data.

Changes of Chemical Structure and Composition of Charcoal by Radiocarbon Pretreatments: Decontamination by ABA and ABOx Treatments

AbstractCharcoal is widely used for radiocarbon dating in archaeological and paleoenvironmental studies. Reliable 14C dating requires appropriate chemical treatment to remove postdeposition contamination from the charcoal samples. This study assesses two pretreatments: acid-base-acid (ABA) and acid-base-oxidation with stepped combustion (ABOx-SC). In addition to 14C, the effects of the treatments on the chemical structure and composition of charcoal were studied using Fourier transform infrared spectroscopy (FTIR) and C/H/O elemental analysis. Samples of pine wood charred in the laboratory at 270, 300, 400, 500, and 600°C, and environmental samples of charred pine wood from pyroclastic flow deposits in southern Kyushu, Japan, were tested. The laboratory-charred samples showed that NaOH treatment removed highly hydrophilic organic components derived from endogenous and exogenous organic materials in the samples and that oxidation treatment caused the oxidative degradation of molecules in samples starting from its edges. The ABA-treated environmental charcoal yielded younger 14C dates than the ABOx-treated samples, probably owing to the effects of remaining organic contaminants bound to the edges of the aromatic molecular structures produced by the original pyrolysis. Meanwhile, it was found that ABA-SC treatment can reduce contaminants as effectively as ABOx-SC treatment. This implies that the stepped combustion (SC), not the chemical oxidation, is the key to reduce contaminant residue left after ABA and ABOx treatments. The results in this study indicate that the investigation of the structural and compositional changes of charcoal during its pretreatment is useful for assessment of the reliability of the 14C ages.

Comparison between luminescence and radiocarbon dating of late Quaternary loess from the Ili Basin in Central Asia

Dust depositions are critical archives for understanding interior aridification and westerly climatic changes in Central Asia. Accurate and reliable dating of loess is very important for interpreting and correlating environmental records. There remains a disparity between luminescence ages and radiocarbon dating of late Quaternary loess from the Ili Basin in Central Asia. In this study, we establish a closely spaced quartz optically stimulated luminescence (OSL) chronology for the 20.5-m-thick Nilka loess section in the Ili Basin. Based on OSL ages, two intervals of higher mass accumulation rate occurred at 49–43 ka and 24–14 ka. We further compare these OSL ages with 23 accelerator mass spectrometry (AMS) 14C ages of bulk organic matter. The results indicate that the OSL and radiocarbon ages agree well for ages younger than ca. 25 14C cal ka BP. However, beyond 30 cal ka BP, there is no consistent increase in AMS 14C age with depth, while the OSL ages continue to increase. These differences confirm the observation that the AMS 14C ages obtained using conventional acid–base–acid (ABA) pretreatment are severely underestimated in other terrestrial deposits in Central Asia, which could be due to 2–4% modern carbon contamination. However, OSL dating is applicable for constructing an accurate chronology beyond 30 cal ka BP. We suggest caution when interpreting paleoenvironmental changes based on radiocarbon ages older than 25 cal ka BP.

The efficiency of charcoal decontamination for radiocarbon dating by three pre-treatments – ABOX, ABA and hypy

Here we report results of a direct inter-comparison of the ability of three radiocarbon pre-treatment techniques to remove radiocarbon contamination introduced by exposing known-radiocarbon-free charcoal made at three different temperatures (300, 400 and 500 °C) to environmental contamination on a rainforest floor for one to three years. The initial charcoal had no measureable radiocarbon, but 14C activity increased after environmental exposure to ∼1 pMC after one year (apparent age of ∼40,000 yrs BP) and ∼5 pMC after three years (apparent age of ∼25,000 years). For the 400 and 500 °C samples, all techniques were able to reduce contamination by >90%. Acid–base oxidation (ABOX) provided the most reliable decontamination, reducing the radiocarbon activity of the one year samples to background, and reducing the radiocarbon activity of the three year samples to 0.04 ± 0.02 pMC or less (apparent age >56,900 yrs BP). The performance of ABOX was superior to that of both acid–base–acid (ABA) and hydrogen pyrolysis (hypy) treatments, with ABA performing better than hypy in most cases. No technique was able to fully remove decontamination from the 300 °C charcoal (although ABOX again removed the most contamination), likely due to the incompletely pyrolized nature of the charcoal which is dominated by aromatic clusters of small ring size. All the techniques rely on removing contaminant carbon faster than indigenous carbon and this condition is not met in the case of charcoal produced at temperatures below ∼350 °C. While all pre-treatments are useful for routine sample processing, the results suggest that ABOX is the only technique that can provide reliable decontamination of charcoal of an age close to the dating limit of the radiocarbon dating technique.

A Simple and Effective Removal Procedure of Synthetic Resins to Obtain Accurate Radiocarbon Dates of Restored Artworks

The issue of contamination in radiocarbon dating is well known and can affect not only archaeological findings but also artworks. In the latter case, a possible source of contamination is represented by the products used during the restoration, e.g. resins of synthetic origin like the well-known Paraloid, applied to wood artifacts as a strengthening and preserving agent. In the case of incomplete removal prior to dating, the resins produce an apparent aging of the samples. Mechanical cleaning using traditional tools and the standard pretreatment acid-base-acid (ABA) protocol are not sufficient to remove such contaminants, while the use of organic solvents, in particular petroleum solvents and chlorine-based products, can be effective. However, the most widely used protocol, based on the Soxhlet extraction system, is very time consuming. Here, in the presence of chloroform-soluble applied products, like the widespread Paraloid B-72, this study proposes the use of a new easily operated pretreatment procedure, developed at INFN-LABEC in Florence, based on the use of chloroform (CHCl3) as solvent and on a simple extraction. First, the effectiveness of this procedure was checked by applying it to remove the resin from wood samples of known age, which had been previously intentionally contaminated by applying large quantities of Paraloid. 14C AMS measurements performed on the test samples before and after contamination and application of the proposed procedure proved its effectiveness for removal, while this was not the case when applying standard ABA protocols. Fourier transform infrared (FTIR) spectroscopy analyses also were used to check the removal of contaminants. The new procedure was applied in two case studies: the wood frame of an altar piece from the Renaissance and a painting on canvas from the early 20th century. For both artworks, the use of synthetic resins was documented in restorations performed a relatively long time ago: the wood frame was restored using just Paraloid, the canvas using a thermoplastic polymer soluble in chloroform. Enough time elapsed for the resins to create cross-linking bonds with the original material. Despite this, the results obtained by 14C AMS dating confirm the reliability of the new chloroform-based pretreatment in removing the contaminations. Also in these cases, spectroscopic techniques were used to compare the effectiveness of the ABA and the new treatments in removing the contaminants.

Assessing natural variation and the effects of charring, burial and pre-treatment on the stable carbon and nitrogen isotope values of archaeobotanical cereals and pulses

The aim of this study is to assess the potential of charred archaeobotanical cereal grain and pulse seed δ13C and δ15N values to provide evidence of crop growing conditions and as a potential component of palaeodietary studies. In order to reliably interpret archaeobotanical δ13C and δ15N values it is necessary to take into account the impact of charring, burial and laboratory pre-treatment procedures. We examine the effects of charring and burial on bulk δ13C, δ15N, %C, %N and C:N ratios in modern cereal and pulse material, and of cleaning by acid–base–acid (ABA) pre-treatment on modern and archaeobotanical charred material. Our study utilised bulk grain and seed samples to help account for within-ear/pod and between-plant variability in δ13C and δ15N values. Heating at relatively low temperatures and for prolonged times (230 °C for up to 24 h) is conducive to the formation of well preserved, undistorted charred cereal grain and pulse seed. Heating for 24 h has a systematic and predictable effect on δ15N values, with increases of around 1‰ on average in cereal grains and pulse seeds, and no consistent impact on δ13C values. Increases in δ15N are likely due to the loss of lighter 14N via N-containing volatiles. Burial (for up to 2 years) and ABA pre-treatment have no significant effects on δ13C or δ15N values. After pre-treatment, however, the %C and %N contents of the archaeobotanical material more closely resembles that of the modern charred grains and seeds, suggesting that archaeobotanical remains accumulate non-structural material during burial but retain their original carbon and nitrogen content. Therefore %C, %N contents and C:N ratios can provide useful criteria for assessing archaeobotanical preservation.