The Society for Archaeological Sciences recently sponsored two sessions that focused on the application of chemistry in art and archaeology at the SciX 2019 Conference, which took place between the 13th and 18th October, 2019 in Palm Springs, California. The session was organised by our very own Andrew Zipkin together with Mary Kate Donais. Here are the abstracts of some of the papers presented in the session:
Spectroscopic Characterization of Historic Fabrics from a Turn of the Century New England Mill
Mary Kate Donais1, Giovanna Beaulieu1, Madaleine Hunt2, and Fred Morris
1. Saint Anselm College
2. Bucknell University
3. Bruker
From coast to Karoo: A radiogenic bioavailable strontium isoscape in South Africa for provenience studies
Andrew M. Zipkin1, Erich Fisher1, Gwyneth Gordon1, Hayley Cawthra2, Kelly Knudson1, and Curtis Marean
1. Arizona State University
2. Nelson Mandela University
The use of radiogenic strontium isotope ratios (87Sr/86Sr) has a long and productive history in archaeological science. Provenience analysis of hard tissues like enamel, bone, and shell relies upon a spatial and chemical reference data set of strontium available for incorporation into the skeleton through diet (bioavailable Sr). The construction of such references, such as an archaeological site baseline or a landscape-scale predictive model (an isoscape), is a rapidly evolving area of research. In 2016, Copeland and colleagues published a plant-based strontium isoscape in South Africa for the middle south coast to ~100 km inland, which we refine and extend here.
In 2018 we collected 149 new, non-agricultural, plants in the Swartberg Mountains, north into the Nama Karoo, and within the 2016 study area to fills gaps in sample coverage. We measured 87Sr/86Sr using a Neptune Multiple Collector-ICP-MS. Using Empirical Bayesian Kriging, we generated a predictive model of 87Sr/86Sr variation across the 2016 and 2018 study areas. Modeling was done in ESRI ArcGIS Pro using rasterized lithology and elevation as explanatory variables. We tested model robustness using random validation subsets to generate new models with the same parameters and compared predicted versus observed 87Sr/86Sr measurements for each model.
87Sr/86Sr ranged from 0.7092 -0.7262 for all samples. The final model had an absolute mean Sr prediction error of 0.0007. Prediction errors were greatest offshore where no samples were collected so mean error is likely overestimated. Congruent with the findings of Copeland et al. 2016, 87Sr/86Sr increased north from the coast and peaked in the Swartberg Mountains. In the Karoo north beyond the Swartberg 87Sr/86Sr values decline; the distance from coast positive correlation with 87Sr/86Sr found by Copeland terminates at the mountains.
Similar strontium ratios are predicted north and south of the Swartberg Mountains making archaeological provenience using a single isotope system ambiguous. Artifacts originating from the mountains should be clearly distinguishable based on 87Sr/86Sr alone. Future work will focus on analysis of modern faunal specimens for taxa of archaeological interest, like ostrich eggshell. This isoscape also has implications for conservation of plant and animal species and forensic research in the region.
Micro- to Nanoscale IR in Heritage Science: The Distribution of Metal Carboxylates in Oil Paint
Xiao Ma1, Victoria Beltran2, Georg Ramer3,4, Georges Pavlidis3, Dilworth Parkinson5, Mathieu Thoury2, Tyler Meldrum6, Andrea Centrone3, Barbara H. Berrie1
1. Scientific Research Department, National Gallery of Art
2. IPANEMA, CNRS
3. Nanoscale Device Characterization Division, Physical Measurement Laboratory, National Institute of Standards and Technology
4. Maryland Nanocenter, University of Maryland
5. Advanced Light Source, Lawrence Berkeley National Laboratory
6. Department of Chemistry, William & Mary
Oil paints comprise pigments, drying oils and additives that together confer desirable properties, but can react to form metal carboxylates (soaps) that may damage artworks over time. Despite substantial research, soap formation and aggregation are not well-understood processes. Here, composition-sensitive techniques (µ-computed tomography, IR microscopy and nanoscopy) are employed to determine the distribution of soaps in a 23-year, naturally aged, oil paint sample of known composition. IR nanoscopy and µ-computed tomography show that low density agglomerates of Al-stearate and a Zn-carboxylate complex with Zn-stearate nano-aggregates in proximity are distributed randomly in the paint. IR microscopy reveals gradients in the distribution of Zn-stearate and Zn-carboxylate complex, which is unrelated to the Al-stearate distribution. The results show that metal soap distributions are more complex and heterogeneous than previously known and offer unprecedented insights for understanding soap formation and their effects on the physical integrity of paintings.
Trace Element Analysis of Archaeological Human Enamel and Bone Apatite: Implications for Documenting Biological Sex and Health Status
Beth K. Scaffidi1, Gwyneth Gordon1, and Kelly Knudson1
1. Arizona State University
Iron metabolism is crucial during childhood development and adult reproduction, when poor dietary quantity or quantity, parasitic, or bacterial infection can lead to macronutrient deficiencies which in turn cause iron-deficiency anemia. When the body detects low iron levels in the bloodstream, erythropoiesis begins, stimulating the kidneys to produce extra blood red blood cells. Chronic iron-deficiency leads to diploic expansion of the bony marrow into the thin cortical bone of the eye orbits, called cribra orbitalia. While one early bioarchaeological analysis of trace element concentrations in tooth enamel did not find lower iron levels in individuals with cribra orbitalia (Gleń‐Haduch et al., 1997), a recent study (Zariſa et al., 2016) reports a significant relationship between decreased iron and cribra orbitalia. The body’s iron stores are also vulnerable during pregnancy, when increased iron demands can cause iron-deficiency anemia. Higher levels of iron in male skeletons have been documented in trace elements of enamel (Gleń‐Haduch et al., 1997) and isotope ratios of bone (Jaouen et al., 2012).
This pilot study examines trace element concentrations in a prehistoric Peruvian skeletal population (n = 36), hypothesizing that iron concentrations will be lower in individuals with cribra orbitalia and in females. Enamel and bone were mechanically and chemically cleaned, bone was ashed, samples were digested in nitric acid, and 36 elemental concentrations were measured on the Q-ICP-MS. Individuals with cribra orbitalia (n = 4) showed lower concentrations of iron in tooth enamel than those without (n = 13) for 54 Fe (t-test, p = 0.033), 56 Fe (p = 0.047), and 57Fe (p = 0.056). Females (n = 4) showed lower concentrations of bone iron than males (n = 13) for 54 Fe (t-test, p = 0.059), 56 Fe (p = 0.059), and 57 Fe (p = 0.059).
These results suggest that amelogenesis records periods of childhood iron deficiency, while female iron depletion is recorded during adult bone remodeling. Trace element concentrations of iron can corroborate bioarchaeological findings of cranial pathology and sex estimations. Combined with stable and radiogenic isotope measurements in incrementally-forming tissues, trace element data can be used to identify periods of metabolic vulnerability.
References cited:
Glen Haduch, E., Szostek, K., Glab, H., 1997. Cribra orbitalia and trace element content in human teeth from Neolithic and Early Bronze Age graves in southern Poland. American Journal of Physical Anthropology: The Official Publication of the American Association of Physical Anthropologists 103(2), 201-07.
Jaouen, K., Balter, V., Herrscher, E., Lamboux, A., Telouk, P., Albarede, F., 2012. Fe and Cu stable isotopes in archaeological human bones and their relationship to sex. American Journal of Physical Anthropology 148(3), 334-340.
Zarifa, G., Sholts, S.B., Tichinin, A., Rudovica, V., Viksna, A., Engizere, A., Warmlander, S.K., 2016. Cribra orbitalia as potential indicator of childhood stress: Evidence from paleopathology, stable C, N, and O isotopes, and trace element concentrations in children from a 17th and 18th century cemetery in JL.kabpils, Latvia. Journal of Trace Elements in Medicine and Biology 38, 131-37.
Strengths and limitations of fecal stanols as a population proxy for Cahokia, Illinois and the Jordanian desert
AJ White1, Varenka Lorenzi2, Lisa Maher1, Lora Stevens2
1. University of California, Berkeley
2. California State University, Long Beach
Fecal stanols are organic molecules that originate in the guts of humans from the microbial degradation of cholesterol and may persist in sediment for hundreds to thousands of years. Fecal stanols deposited in sediment provide evidence of trace human waste products, and are used as a proxy for measuring population change over time. We compare fecal stanol data from Cahokia, Illinois and Kharaneh IV, Jordan to discuss the strengths and limitations of using fecal stanols in paleodemographic studies.
We analyzed sediment samples for fecal stanol content through overnight soxhlet extraction with dichloromethane, derivatization into trimethylsilyl ethers through a reaction with N,O-bistrifluoroacetamide, and gas chromatography/mass spectrometry (GC/MS). We identified stanol compounds by comparing characteristic mass spectra fragmentation patterns and gas chromatographic retention times of samples with chemical standard solutions and quantified samples by comparing peak areas with a calibration curve and the relative response factor of an internal standard.
Fecal stanol analysis produced viable data for the Cahokia region that approximates previous population reconstructions. Although we identified fecal stanols in Kharaneh IV sediments, their concentration is similar in on- and off-site contexts. We analyzed camel feces for stanol content and found that camels produce a significant amount of the fecal stanols found in human feces. The fecal stanol record at Kharaneh IV is best explained by historic and modern grazing of domesticates, including camels, over the site, and fecal stanols from their waste migrated into and contaminated older archaeological sediments.
Fecal stanols may be used to track ancient population change, but archaeological, geomorphological, and analytical factors constrain their utility. We find that fecal stanols may be mobile in porous sediments and that waste from modern domesticates can contaminate older deposits.
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