Schlagwort-Archive: petrography

Performing XRD analysis on Nile clay Nubian- and Egyptian-style samples from Attab and Ginis

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Exams never end, not just for humans but even for archaeological artifacts.

Already before the Christmas break, I had happily returned to the lab, this time to prepare a new bunch of ceramic samples to undergo X-ray powder diffraction (XRPD) analysis. Thanks to a new cooperation with the TU München, and especially with Prof. H. A. Gilg (Chair of Engineering Geology) we decided in fact to complement our iNAA and OM analyses with this new laboratory methodology, with the aim of expanding our knowledge on the composition, provenance and technology of production of our Nile clay samples. All in all, we preliminary selected 30 ceramic specimens, among Nubian- and Egyptian-style sherds from the 2022 and 2023 excavated sites at Attab West and Ginis East. To this sample, we added a replica in modern Nubian (from Abri) Nile clay manufactured by us during our last workshop in Asparn.

Generally speaking, X-ray powder diffraction analysis is a well consolidated analytical technique used in the field of archaeometry and ceramic technology to determine the mineral phases present in the pastes, including those clay phases which are typically not visible under the microscope. This technique also provides information on the firing process the pottery went through. Certain minerals (e.g., calcite as one of the most known) can in fact degrade, disappear or be altered at given temperatures because the crystalline structure collapses through the process of dehydroxylation (Magetti 1982; Rice 1987). The analysis itself based on the phenomenon of diffraction of electromagnetic radiation, by exploiting the fact that X-rays falling on crystalline planes in minerals are reflected at varying angles (Velde and Druc 1999; Quin 2013). Hence, each mineral type will produce a characteristic X-ray diffraction spectrum with diagnostic peaks placed at given angular distances (expressed in degrees 2θ), allowing the qualitative identification of the minerals present within the ceramic sample. The heigh of those picks permits otherwise a semi-quantitative estimation of the ratios in which minerals are more or less represented.

Figure 1 – Lab kit for the preparation of samples for XRD analysis. Photo by G. D’Ercole.

Sample preparation is pretty much straightforward although partially destructive. The procedure requires that a tiny portion of the sherd be ground up (about 1g of powder) by hands with an agate mortar and a pestle, alike those used for iNAA, pressed in the mounting smear slide, and then put into the instrument. Proper pulverization and homogenization are crucial to achieve highly quality XRD data.

Figure 2 – Pulverization of the sample by hands in the agate mortar. Photo by G. D’Ercole.

The sample needs to be as representative of the ceramic sherd as possible – for this reason, it is sometimes advisable to grind a larger quantity of powder and above all finely ground so as to prevent larger crystals (e.g., coarse quartz grains) from interfering with the measurement. This latter can be carried out with different timing and levels of accuracy depending on whether one wants only a rough semi-quantitative estimate of the mineral phases in the sample or more accurate information.

Figure 3 – First set of potsherds ground up and ready to be analysed by XRD analysis. Note the diverse powder colours from black (reduced fired Nubian samples) to reddish-brown (oxidized fired Egyptian sherds). Photo by G. D’Ercole.
Figure 4 – Samples ready in the mounting smear slides. Photo by G. D’Ercole.

In performing XRD analysis, our main archaeological questions were the following:

  • Can we recognize the use of different clay raw materials for the different sites/locations (e.g., Attab, Ginis…);
  • Can we differentiate between Nubian- (also Pan-Grave) vs. Egyptian-style samples;
  • Can we differentiate between the different ceramic types and wares;
  • Can we demonstrate the intentional addition of tempers (calcite and/or quartz and/or feldspar and/or mica) in particular samples?
  • Can we know more about the firing process (i.e., firing temperatures) the ceramics went through?

Currently, together with Prof. Gilg, we just started to interpret the results of the first diffractograms. The data are not always straightforward to read and the differences between the various samples look sometimes very subtle – on the other hand our Nile clay samples have used us to significant challenges for many years already!

Preliminary, we can say that, based on the diagnostic mineral phases in the various spectra, it was possible to recognise four distinct groups or types of samples. These groups do not depend on the main phases (quartz or feldspar) as these are present in nearly homogenous amounts in all samples. Rather, some differences can be spotted in the clay minerals. Whether these latter can be ascribed to different clay sources, preparation recipes, or eventually the pot production (i.e., firing) has yet to be fully assessed.

References

Maggetti, M. 1982. Phase Analysis and its Significance for Technology and Origin. In J. S. Olin and A. D. Franklin (eds.), Archaeological Ceramics: 121−133. Washington, Smithsonian Institution Press.

Quinn, P. S. 2013. Ceramic Petrography: The Interpretation of Archaeological Pottery & Related Artefacts in Thin Section. Oxford, Archaeopress.

Rice, P. M. 1987. Pottery analysis. A sourcebook. Chicago, University of Chicago Press.

Velde, B. and Druc, I. C. 1999. Archaeological Ceramic Material. Origin and Utilization. Berlin Heidelberg, Springer-Verlag.

Good news during very sad times for Sudan: our DiverseNile 2023 samples successfully sent to lab for INAA and OM analyses

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Archaeologist is a meaningful career although our amazing job is constantly challenging under many respects and it often is physically and emotionally demanding. This is especially true for those among us who work in the field and even more for archaeologists who are part of projects, like ours, that investigate very remote and fragile geographical areas. And Sudan was in the past, and is clearly still nowadays, an extremely fragile and unpredictable land both in terms of its environmental and climatic conditions, resources, borders, cultural entities, and interregional socio-political relationships. This can be certainly attributed to the vastness of the country and to its long history of intricate and fragmented cultural, linguistic and religious identities which intertwine with an alike complex mosaic of many diverse and complementary landscapes and ecological niches.

Having said that, with these words, I do not want in any way to justify under the umbrella of the general geo-political complexity of the country, the horrible conflicts and fighting that have been going on in the capital city of Khartoum for days now and that make us seriously fear for the lives of our colleagues and friends there, as well as for the possibility of being able to return to work in our beloved Sudan. This insane war has in fact to do with geo-political balances and power games, and at the moment I consider myself blessed to have still had the privilege of having a successful field season there and hence returning just in time to get safely back home, in Munich – our team left Khartoum just five weeks ago, before all this catastrophe started!

Even more grateful we can consider ourselves, although in the last days ours is not just normal business, to manage to successfully export to Germany all our bunch of samples for laboratory analysis. And this was possible as usual thanks to the kind cooperation of our inspector and friend, Huda Magzoub, and of the NCAM in Khartoum.

A few days ago, just before the Easter break, my desk, or rather, every flat surfaces of my office (!) was still covered by a multitude of tiny, beautiful ceramic sherds for analysis. These samples, selected during the two weeks of field season I spent in Ginis, include a total of 131 specimens, attributable to Nubian-style and Egyptian-style ceramics made in Nile clays. Of these, 129 were eventually destinated to INAA and have been already successfully delivered to the AI of Vienna, where they are now in the wise hands of our colleague, Johannes Sterba. 28 intended for Optical Microscopy were additionally sent to Prague and are currently in the process of being manufactured as polished thin sections.

The sample incorporate mainly ceramic material from the Bronze Age sites in the area of Ginis and Attab, and specifically from the two excavated settlement sites of Attab West 001 ( 60 sherds in total) and Attab West 002 = Vila Site 2-S-54 (17 sherds in total), and from the cemetery GiE 003 in Ginis East (44 sherds in total). To these are added 10 samples from a surface collection conducted by our PI, Julia Budka, in the district of Kosha East (Kerma cemetery 3-P-7).

All in all, this material is highly significant in terms of diachronic representativeness of the area, covering in fact a wide time span from the Middle Kerma to the Kerma Classic and up until the 18th Dynasty of the New Kingdom period. Furthermore, these samples appear extremely promising with our general aim of understanding cultural diversity and investigating interregional and local social relationships between Egyptian and Nubian entities, comprising exceptionally not only Nubian Kerman material but also ceramic wares and types potentially attributable to the Pan-Grave cultural sphere (from Trench 5 at GiE 003).

I was glad to once again have a pleasant déjà vu of myself photographing, documenting, and packing these tiny samples that are now waiting to be analysed, while I am now busy in entering each of them in our Samples FileMaker DB.

Looking forward to revealing more about the inwardness of these tangible precious testimonies of Nubia’s Bronze Age material culture, I wish a bit of rest, peace, and hope for our beloved Sudan and mostly for all people and citizens who are now in danger because of this unjust violence.

Tentative steps towards reconstructing cultural diversity in the Attab to Ferka region through material studies

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One of our objectives within the DiverseNile project, to reconstruct cultural encounters based on the material record by the detailed assessment of the most important productive activities, technologies and foodways, has received plenty of new material evidence during the 2022 excavation season. Most importantly, thanks to the support of NCAM and especially our inspector Huda Magzoub, I was able to export a selection of pottery samples for scientific analysis to Germany. These new samples from our excavations in Ginis East (sites GiE 001 and 003) and Attab West (site AtW 001) are of huge importance for the project, especially because due to the restrictions caused by the corona pandemic for archaeological fieldwork in the last two years, we could until now only investigate the petrography of ceramic samples from Dukki Gel.

Such a privilege: unpacking ceramic samples in Munich just one month after excavating the sherds and their contexts in Sudan!

This ties in with what our PostDoc Giulia D’Ercole has summarised in a recent paper: „For over seventy years, theoretical approaches and methods of classification of ceramic objects in Sudan have gradually changed, as have the perspectives and the general purposes of archaeological research. In general, scholarly attention has progressively shifted from forms (i.e., decoration and shape) to mineral and chemical compositions of ceramics and vessel contents (i.e., petrographic, compositional, and organic residue analyses)“ (D’Ercole 2021). This changed focus already influenced our research within the framework of the AcrossBorders project and is now continued with the DiverseNile project.

The analysis of the material culture in Work Package 3 of the DiverseNile project is undertaken from a multi-perspective level, including scientific analyses focusing on provenience studies (e.g. ceramic petrography and iNAA, see already D’Ercole and Sterba 2018). For the ceramics, we will combine macroscopic observations with analytical approaches and evaluate the results of optical microscopy (OM) and chemical analyses (XRF and iNAA) in conjunction. Together with LMU colleagues, Giulia has also introduced Raman spectroscopy as a new application to answer various technological questions, in particular on the manufacturing stages of production and firing of the pots. This will especially help to understand questions about local productions and influences of Nubian ceramic traditions for preparing wheel made pots in the Middle Nile region.

In the last days, I was busy preparing the documentation of our new ceramic samples from Ginis East and Attab West. I selected twenty-one samples for optical microscopy (OM) and thus for the preparation of thin sections, while I will bring 108 samples later this week to the Atominstitute in Vienna where they are being analysed for instrumental Neutron Activation Analysis (iNAA) by our colleague and external expert in the project, Johannes Sterba.

Documenting a set of early New Kingdom samples from Attab West.

The new samples comprise sherds of various surface treatments and different fabrics of the Kerma ceramic tradition as well as diverse Egyptian style wheel made samples of which the majority seems to attest to a local pottery production in the Attab to Ferka region. Photographing the samples, I was again struck by the extremely interesting appearance of the material from the domestic site AtW 001. Although I know that the scientific analyses will take some time and I need to be patient, I cannot wait to integrate the results from iNAA and petrography with my archaeological assessment and macroscopical observations and discuss them further with Giulia and Johannes.

Like Aaron M. de Souza and Mary F. Ownby very truly remarked in a recent paper: more micro-analyses of Nubian material culture need to be undertaken to achieve a better understanding of cultural diversity in the Middle Nile (de Souza and Ownby 2022, 55).

References

D’Ercole, G. 2021. Seventy Years of Pottery Studies in the Archaeology of Mesolithic and Neolithic Sudan. Afr Archaeol Rev 38, 345–372. https://doi.org/10.1007/s10437-021-09432-y

D’Ercole, G. and Sterba, J. H. 2018. From macro wares to micro fabrics and INAA compositional groups: the Pottery Corpus of the New Kingdom town on Sai Island (northern Sudan), 171–183, in: J. Budka and J. Auenmüller (eds.), From Microcosm to Macrocosm: Individual households and cities in Ancient Egypt and Nubia. Leiden.

de Souza, A.M., Ownby, M.F. 2022. Re-assessing Middle Nubian cultural constructs through ceramic petrography. Afr Archaeol Rev 39, 35–58. https://doi.org/10.1007/s10437-022-09473-x

First preliminary remarks on the petrography of the Dukki Gel ceramic samples

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In the last few weeks I haven’t been very present in our blog since I spent much time sitting at the microscope of the Department of Earth and Environmental Sciences of the LMU, just nearby to our office, examining and documenting the first batch of ceramic samples from the site of Dukki Gel. These samples have been included as a reference collection within our DiverseNile project thanks to the kind agreement of the excavator, Charles Bonnet, and the responsible ceramicist Philippe Ruffieux. Philippe has already studied all of these samples within their context and we can now address fresh questions within the DiverseNile work packages and with scientific analysis.

In times of the Covid pandemic, the procedure to access the laboratories is rightly strict: registration is mandatory before working in the microscopy room, only a maximum of three people are allowed to work simultaneously in the lab and of course we are required to wear medical masks and disinfect all devices and workspace at the end. All this will seem obvious, but what I personally find curious is the contrast between the meticulousness of the analytical procedure, further complicated by the current Covid rules, and the simple and tangible nature of the ancient ceramics, whose immense  anthropological and material complexity, and huge archaeological interpretative potential is all enclosed in a thin section of just 30 microns thick.

In my last blog post – I introduced the method I use for the classification of the ceramic samples and the layout within the Filemaker database which I specifically designed for the purpose of the petrographic study.

So far a total of twenty-one ceramic samples from Dukki Gel has been analysed by optical microscopy (OM), while forty-three samples are currently located at the Atominstitute in Vienna where they are being analysed for instrumental Neutron Activation Analysis (iNAA) by our colleague and external expert in the project Johannes Sterba.

Most of the samples for OM (18 out of 21) are Nubian vessels among which are cooking pots (both basketry impressed and incised ware), jars, globular vessels and also fine black topped Kerma ware. Further, three Egyptian-type vessels (two red slipped bowls and one fragment of a bread mould) were analysed under the microscope.

Petrographically, the Nubian samples from Dukki Gel appear quite homogeneous in term of their composition, displaying mineralogical and textural features which also resemble very much the petrography of the Nubian samples analysed from the New Kingdom town of Sai Island (see D’Ercole and Sterba 2018; D’Ercole in prep.). Differences in the textural features, in the proportion of some specific mineral phases, and in the amount and type of the organic tempers contained in the paste allowed distinguishing four principal petrographic groups or micro fabrics. The first group is characterized by a very sandy framework with a dominant grain size in the class of silt to very fine-grained sand, a good sorting of the non-plastics and very few organics mainly small and tubular in shape. The second group also displays a sandy framework, sorting is moderate with some medium sized rounded quartz and feldspar possibly added as temper, and common tubular organics partially carbonized and moderately aligned. Group 3, to which belongs the majority of the analysed samples, is sandy, moderately sorted, with common to abundant organics, either partially or completely carbonized, heterogeneous in shape and size,  and possibly referring to various parts of plant remains (including stem, glume, palea, and lemma?) (Fig. 1) and also herbivore dung. Finally, the fourth group of Dukki Gel Nubian samples contains abundant heterogeneous organics similar to group 3 but also large carbonate inclusions of microcrystalline calcite most likely intentionally added as tempering material. To this last group, which does not show a real comparison with the material from Sai, where the presence of calcite was ubiquitous and seemed a natural component in the clay source/ soil rather than a tempering agent, refers exclusively cooking pots with basketry impressions and a single jar.

Figure 1 – Detail of organic inclusion with visible plant cell structure from Sample DG-17. PPL micropho by G. D’Ercole.

All in all, similarly to what was observed for Sai Island, the petrofacies of the Nubian ceramics is very homogeneous and points to the selection of clays, or better soils, derived from local Holocene Nile alluvia, with a composition very similar along the various sectors of the Nile river (D’Ercole and Sterba 2018). These ceramics were possibly tempered with some medium- and coarse-sized aeolian sand or with quartz grains drained by the local river systems. Technologically, the amount and type of the organic material added to the paste (more or less abundant and selected) makes the main difference and allows distinguishing among various sub-recipes or ways of doing the vessels. Further, the orientation of the voids left by the combustion of the organic matter into the paste permits to recognize among the use of different manufacturing techniques. Specifically, in the cooking pots with basketry impressions which were built on a mat, the organics appear generally well or moderately aligned with a prevalent presence of longitudinal features like stems or plant stalks (Fig. 2a). Differently, in those pots (e.g., globular pots, bowls) built with the coiling technique, the organics show mainly a poor alignment and a specific orientation that indicates the ‘relict’ coil features (Fig. 2b). The black topped and the fine polished Kerma ware generally contain less organics, these latter are also smaller in size indicating either the use of herbivore dung and/or a selection of added plant remains.

Figure 2a – Thin section scan of Sample DG-18 (Nubian cooking pot). The good alignment of the pores structures and of the voids and relicts left by the combustion of the organics indicates that this vessel was built on a mat. Image by G. D’Ercole.
Figure 2b – Thin section scan of Sample DG-17 (Nubian large bowl). The specific concentric alignment of the pores structures and of the voids and relicts left by the combustion of the organics indicates that this vessel was manufactured with the coiling technique. Image by G. D’Ercole.

Highly interesting in the sample from Dukki Gel, is the presence of a jar with a roughly polished / wet-smoothed black surface which although showing clear Nubian technological exterior features is characterized by a coarser and sandier fabric with more abundant feldspar and granitoid rock fragments resembling certain Egyptian cooking pots (Fig. 3). This sample, so far an unicum in our selection, points to an hybridization of Nubian and Egyptian traditions (this time with the intersection of some performance of ‘Egyptian’ criteria to a general Nubian technological and stylistical formula) and well supports our overall theoretical framework and working approach on the complexity and diversity among various Nubian local narrative experiences and conceptions of material culture.

Figure 3 – Sample DG-22 (Nubian jar) with roughly polished / wet-smoothed surfaces characterized by a sandy fabric rich in alkali feldspar. Photo by G. D’Ercole.

Hopefully by the end of this month, we also will have the first set of chemical data from the reference collection from Dukki Gel in our hands which we will then compare with the macroscopic evidence and with these petrographic remarks.

References

D’Ercole, G. In prep. Petrography of the pottery from the New Kingdom town of Sai, in: J. Budka, with contributions by G. D’Ercole, J. Sterba and P. Ruffieux, AcrossBorders 3: Vessels for the home away from Egypt. The pottery corpus from the New Kingdom town of Sai Island. Archaeology of Egypt, Sudan and the Levant. Vienna.

D’Ercole, G. and Sterba, J. H. 2018. From macro wares to micro fabrics and INAA compositional groups: the Pottery Corpus of the New Kingdom town on Sai Island (northern Sudan), 171–183, in: J. Budka and J. Auenmüller (eds.), From Microcosm to Macrocosm: Individual households and cities in Ancient Egypt and Nubia. Leiden.

Designing the petrographic documentation for the ceramic samples of the DiverseNile project

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Documentation is the bread and butter of archaeological research. Archaeologists are daily committed to documenting everything: sites formation processes, dwellings, funerary remains, and above all the various products of material culture.

Any method of documentation, from the most essential and traditional (i.e., technical drawing of archaeological strata and finds) to the most elaborated (i.e., image-based 3D-modelling of artefacts, human remains, and sites) constitutes a fundamental step toward archaeological reconstruction. Documentation mainly serves the archaeologist to record and understand the material remains, settlement and funerary features identified during the archaeological excavation and to leave a trace of it. Also, through documentation, a preliminary process of interpretation and critical reading of the data is carried out. Furthermore, the system we adopt to document and classify archaeological data is not unbiased, rather it already implies a methodological choice and a specific scholarly interpretative approach.

As responsible, within the Work Package 3 of the DiverseNile project, for the technological and compositional analyses of the ceramic materials, I want to outline the method I use for the petrographic classification of the ceramic samples which we are going to analyse from the new concession area in the Attab to Ferka region and from our reference collections (e.g., the AcrossBorders ceramic samples from Sai Island; the New Kingdom/Kerma-Dukki Gel pottery samples; see also D’Ercole and Sterba 2018).

Generally speaking, petrography, via optical microscopy (OM), is a well-established procedure employed to examine ceramic objects and identify the source of clay raw materials and tempers used to manufacture the vessels (Fig. 1). This technique allows answering to crucial archaeological questions on pottery provenance and technology.

Figure 1. Example of ceramic thin section illustrating some common features documented for petrographic analysis. Adapted from Smith 2008: 74, Fig. 6.1.

In Sudanese archaeology, the interest in provenance and technological studies on pottery started approx. 50 years ago. In 1972, Nordström, referring to the work of Anna Shepard (1956), produced a systematic publication on early Nubian ceramics from the region of Abka-Wadi Halfa and defined the term fabric meaning the set of the compositional and anthropogenic characteristics of the ceramic material that could be determined by microscopic observation and comprised both the composition of the groundmass (or clay matrix) and non-plastic inclusions plus the potter’s technological choices adopted to make the vessel.

For the study of the ceramic material of our DiverseNile project I have designed a specific petrographic layout within the Filemaker database of the ceramic samples (Fig. 2).

Figure 2. Layout of the petrographic database designed for the DiverseNile project.

The petrographic layout includes information on the archaeological provenance and dating of the samples. It also correlates the micro fabric or petrographic group to the macroscopic evidence, that is the visual description, shape, function, and macro ware of the ceramic specimens. The consecutive entries inform on a) the groundmass or clay matrix of the sample (i.e., colour, homogeneity and optical activity); b) non-plastic inclusions (i.e., sorting, dominant grain size, maximum grain size, abundance, and mineral composition); c) plastic inclusions (i.e., clay pellets, argillaceous rock fragments etc.); d) porosity (i.e., voids abundance, type, dominant size, iso-orientation); e) organics (i.e., abundance, type, dominant size). The database also notifies on the firing regime of the ceramic sample (i.e., oxidised, reduced, reduced with narrow ox margins, dark core due to insufficient ox, oxidised to reduced). Finally, a graphic field incorporates the microscopic photos of the thin section taken under both cross-polarised (XPL) and plane polarised (PPL) light. Comments, possible comparison with other samples, and a link to the iNAA compositional groups are included as further relevant information.

The purpose of this database is to simplify the data entry of the petrographic evidence and to standardize it according to an easy-to-use, flexible, and consistent classificatory system that embraces the main information on the composition and technology of production of the ceramic data (see among others Quinn 2013).

At a subsequent step, this information will be intertwined with the results obtained from the other laboratory analyses and eventually with the archaeological data to provide a further analytical and interpretive tool for understanding the diversity and complexity of the material culture of the human groups living in the periphery of the Egyptian towns in Sudanese Nubia.

References

D’Ercole, G. and Sterba, J. H. 2018. From macro wares to micro fabrics and INAA compositional groups: the Pottery Corpus of the New Kingdom town on Sai Island (northern Sudan), 171–183, in: J. Budka and J. Auenmüller (eds.), From Microcosm to Macrocosm: Individual households and cities in Ancient Egypt and Nubia. Leiden.

Nordström, H. – Å 1972. Neolithic and A-Group sites. Uppsala, Scandinavian University.

Quinn, P. S. 2013. Ceramic Petrography: The Interpretation of Archaeological Pottery & Related Artefacts in Thin Section. Oxford, Archaeopress.

Shepard, A. O. 1956. Ceramics for the Archaeologist. Washington, DC: Carnegie Institution of Washington.

Smith, M. S. 2008. Petrography, Chapter 6, 73-107, in: J. M. Herbert, T. E. Mc Reynold (eds.), Woodland Pottery Sourcing in the Carolina Sandhills. Research Report No. 29, Research Laboratories of Archaeology, University of North Carolina at Chapel Hill.