MicroCT- tomography for the study of mineral and organic inclusions in ceramics of the Stone Age sites (North-western Russia)

Transcription

1 MicroCT- tomography for the study of mineral and organic inclusions in ceramics of the Stone Age sites (North-western Russia) A.M.Kulkov 1, M.A.Kulkova 2 1 SPbSU, Uljanovskaja st.1, SPb, Russia 2 Herzen State Pedagogical University, Moika emb. 48, SPb, Russia Aims The reconstruction of pottery technology is the important for understanding of the human society development and cultural and historical processes. Ceramics were the first artificial material developed by man. To construct the pottery the series of complex technological operations are applied that includes the choice of raw material, recipes of ceramic pastes, moulding techniques and firing conditions. The reconstruction of each of these operations is the complicated task also. One of these tasks is the determination of ceramic paste composition, the natural and artificial additives. In this connection the application of the high resolution 3D computed microtomography (microct) is a powerful technique used to visualize and characterize the internal structure of objects. It is a non-destructive method that produces images of the internal structure of an object which does not need to be previously The great advantage of microtomography is that quantitative information such as volume, size, shape, distribution and connectivity of the pores can be obtained through the entire 3D volume of the samples, from micro-scale to nano-scale [1,2]. Along with the organic inclusions from clay material of ceramics, the different types of organic temper could be added by man. During pottery firing the organic admixtures have been burned. Therefore, the assessment of their nature is difficulty. The microct-method is the valuable instrument for the reconstruction and visualization of porosity that were remained after organics has burned. The aim of this work is the analysis of composition and distribution of mineral and organic inclusions inside of ceramic body. Method The samples of Early Neolithic ceramics were scanned using the SkyScan 1172 device of the Geomodel Research Centrum of Saint-Petersburg University with a beam energy of 120 kv, a flux of 80 μa and aluminum filter with a resolution of 4-6 μm, performing a 180-degree rotation with a step size of 0.4 degrees. CTvox and CTan has been used for the visualisation of a void caused by organic temper in fragments, shells, distribution of sand inclusions. The chemical composition of mineral inclusions was determined by the SEM-EDX. Results According to microct analysis there are several types of artificial admixtures in the composition of ceramic pastes that have differences from the clay material on their density and the character of distribution. The several Neolithic ceramic sherds from Podolie 1-3 site located in the Southern Ladoga Region were studied. The pottery is dated by cal BC and they are decorated by Pit- Comb and Comb ornamentation (Gusentsova et al. 2015). The results of micro CT are presented in the Figures 1, 2.

2 Fig.1 Ceramics sherds (samples #1741,#1742) and their microct viewings Fig.2 Ceramics sherds (samples #1743,#1744) and their microct viewings

3 1741. As a temper the fine grinded asbestos (tremolite Ca 2Mg 5(OH) 2[Si 4O 11]) - 29,2% and grog (crushed ceramics) 5% were added As a temper the crushed granite (6,8%) was used. The size of grains is 2-3 mm As a temper the Quarz sand (15%) and cutting plant (34,5%) were added. On the base of chemical composition the material inside of porous has the same composition that is clay, therefore the shells and feather did not use. On the data of 3D porous visualization the parts of grass were recognized (Fig.3). The analysis of sand fraction on the base of microct shows the binary character of distribution that allows to conclude that sand was added as temper. Fig.3. Pores after grass stem and lives in ceramics sherd (sample #1743) As a temper a crushed shell (15%) was used. The size of shell particles is 2-3 mm. The ratio of porosity, temper and clay for these ceramic types is present in the Table 1. Tabl. 1. The components of ceramic pastes (in %) on data of mct. # sample Name of Temper,% Total Open Close Clay,% temper porosity,% porosity,% porosity,% 1741 asbestos 29,2 10,8 9,7 1, granite 6,8 14,1 13,9 0,2 79, sand+plant n/o 35 34,5 0, shell n/o 15,8 13,7 2,1 n/o One sherd belongs to the Early Metal Age ceramics ( cal BC) from Okhta 1 site, located in Saint-Petersburg City (Gusentsova et al. 2012) As a temper the feather, down and crushed shell were used. On the Figure 4 that shows the 3D porous visualization there is clear differences between porous from shells and feather. The 3D structure of feather stem and barbs allows to suggest that was the waterfowl.

4 The last sherd is a part from Early Neolithic pottery (about 5500 cal BC) from Serteya XIV site located in Dnepr-Dvina basin (Mazurkevich et al. 2015). Fig.4 Pores after crushed shells and feathers in ceramics sherd (sample #3363) 231. On the data of microct ceramics were tempered by sand. In the clay matrix the round inclusions were found. The character of their distribution is not uniform and their density is much higher than clay. The amount of these inclusion is about 3-4 %, total porosity is 40%. The composition of these inclusions was determined by SEM-EDX method as Fe-Mn oolites (Fig.5). Fig.5. Ceramics sherd #231, its exterior (left upper), microct reconstruction and SEM-EDX maps of Fe and Mn (left down) and distribution of oolites in sample volume (right)

5 Conclusion The investigations of inner structure of archaic ceramics with help of mct-tomography allow to differ the various mineral inclusions on the base of their density and character of distribution. It is important for differentiation the natural and artificial (temper) additives. The criteria of sand distribution and its amount give possibility to determine whether sand was added as temper or it was the natural content of clay material. One of the most important things in the study of ceramic structure is the reconstruction of results of detail visualization of porosity in a shard. 3D void visualization allows to determine the pores occurred during burning of different types of organics. It needs to note that it is difficult to differ by visual and in the thin sections the pores from shell, feather and cutting plant especially if the firing temperature was more than 780 o С when the shells are decomposed. There are nothing any traces of material in the ceramic body. In this case 3D reconstruction of porosity is essential. Literature 1. M.F.S.Oliveira, I.Lima, L.Borghi, R.T.Lopes, X-ray microtomography application in pore space reservoir rock, Applied Radiation and Isotopes, Vol 70, pp , (2012). 2. A. C. Machado, I. Lima, R. T. Lopes, Effect of 3d computed microtomography resolution on reservoir rocks, Radiation Physics and Chemistry, doi: /j.radphyschem (2013). 3. Gusentsova T.M., Sorokin G.E.. The first site of neolitic and early metal age (Ohta 1) at St-Petersburg //Mezolit and Neolit of East Europe: chronology and culture культурное interactions SPb.: IHMC RAS/MAE RAS, (in Russian). 4. Gusentsova T.M., Sapelko T.V., Ludikova A.V.,Kulkova M.A., Ryabchuk D.V., Sergeev A.U., Holkina M.A /Archeology and paleogeography of Podolje 1 site at South Ladoga region //Archeology of lake settlements at IV-II th bc: chronology of cultures and climatic rithms. SPb., SOT «Pereferja» С (in Russian) 5. Mazurkevich A.N., Dolbunova E.V., The oldest pottery in hunter-gatherer communities and models of Neolithisation of Eastern Europe Documenta Praehistorica XLII, pp