Schlagwort-Archive: pottery analysis

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.

Excavation in Attab and Ginis, week 5 of the 2023 season

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Week 5 of our 2023 field season just flew by, especially because of several very disturbing incidents.

On the positive side, we managed to close excavations at site AtW 001, postponed further exploration of Vila site 2-S-54 to next year and made good progress in the Kerma cemetery GiE 003.

AtW 001 will require much post-excavation work – we documented several still standing mud brick walls, there were clearly several phases of building and use. Chloe Ward who did an excellent job this season has already arrived back in Munich and is busy finalizing the stratigraphy and feature description as well as other details from her desk back home.

A small glimpse of the final state of site ATW 001 with various remains of mud brick walls.

Most importantly, we managed to reach the same ashy layer on the alluvial surface like in 2022. It is now also clear that apart from a slight natural slope, most of the mound-like appearance of site AtW 001 is actually composed of settlement debris and especially mud brick debris in several layers.

Excavations at Vila site 2-S-54 came to an unexpected stop – the material culture of the mud brick and stone building is really intriguing and currently being studied by Giulia D’Ercole and myself. Giulia arrived this week and already prepared all the samples from site 2-S-54 we will export for iNAA analysis in order to investigate the provenience of Nile clay wares (see earlier posts by Giulia on this subject, e.g. https://www.sudansurvey.gwi.uni-muenchen.de/index.php/2020/12/22/where-are-you-from-a-diverse-material-perspective-on-this-common-tricky-question/). Of course, a substantial part of our 2023 samples will come from site AtW 001, but here I am still busy reconstructing the large number of complete vessels. More than 10.000 sherds need to be checked for matching pieces and this clearly takes a while.

One of the most remarkable vessels I am currently reconstructing – an „in-between“ cooking pot, combining Egyptian and Nubian pottery traditions.

Finally, much progress was made in the Kerma cemetery GiE 003, where work in Trench 3 was concluded (and yielded a total of 14 new Classic Kerma burial pits, closely resembling our results from 2022) and excavation in Trench 4 is still ongoing. All tombs have been looted in antiquity, most probably in Medieval times, but there are still substantial remains of material culture, especially pottery, beads and remains of wooden funerary beds.

Work in Trench 4 is still ongoing.

One of the most remarkable finds of this season is a small ivory bracelet from Tomb 33 in Trench 3. It was clearly used for a long time, was broken at a certain point, and then repaired by means of repairing holes – this is how we found it deposited in the burial pit. An intriguing object in many respects!

The broken but repaired and thus complete ivory bangle from Tomb 33.

Jose M.A. Gomez, Huda Magzoub, Sofia Patrevita and our team of local workmen got new reinforcement this week: two students from Al-Neelain University in Khartoum have joint us. Tasabeh Obaid Hassan and Mohamed Abdeldaim Khairi Ibrahim have been already extremely helpful at the excavation in the Kerma cemetery and for example very quickly learned to measure targets and outlines of stratigraphic units with the totalstation.

I am very grateful to all team members and looking much forward to the results of week 6!