Achaeometrical Research in Hungary II., 1988

ANALYSES - POTTERY - György SZAKMÁNY: Insight into the manufacturing technology and the workshops: evidence from petrographie study of ancient ceramics

originate from the clay itself may also occur in small amounts. These include carbonates, micas, chlorites and often fossils. The clasts were determined qualitatively, quantitatively or semiquantitatively. The quantitative method is the volume determination and a grid was used for estimation. This is the best-recommended method because the results are more useful than those obtained by semiquantitative estimates. In addition to the determination of clasts, we carried out careful textural and structural observations on the ceramic samples. This observation offers an insight into the ancient technological features used in producing ceramics. Mineralogical and petrographical composition of the ceramics The following clasts occur in the ceramics under discussion here: quartz, feldspar, mica, carbonate grains, quartzite, siliceous (opalic) fossils, accessories, igneous and metamorphic rock fragments, pottery fragment inclusions. Quartz is the most frequently found type of clast in ceramics. Its amounts almost always exceeded 30 volume%, but sometimes reached 80 volume%. The origins of quartz may be igneous or metamorphic (the latter is characterised by undulatory extinction). For example, great amounts of metamorphic quartz were found in the Dressel 6B amphoras (JÓZSAetal. 1994). Feldspar grains are plagioclase or K-feldspar crystals. If the plagioclase has a polysynthetic twin (characteristic of mainly igneous plagioclase), it can be easily distinguished from the K-feldspar. It is, however, very difficult to identify different types of Kfeldspars. Only the microcline is recognisable if its cross-hatched twinning becomes visible. The presence of microcline indicates the granitoid-syenitoid (and very rarely granulitic) origins of the clasts. Zoned plagioclase is evidence for the volcanic rock source of the clasts. The composition of the plagioclase is also indicative the source rocks, however, the exact determination of the plagioclase is possible only using electron microprobe analyses. Feldspar grains are very common clasts, but they usually occur in small amounts (traces to a few volume%). Micas (biotite and muscovite) occur in almost every type of ceramics in small but near-constant quantities (a few volume%). Sometimes their amounts increase (for example in some samples from Szőny, in which the amounts of muscovite exceeded 25%). Great amounts of mica may be indicative of metamorphic source rocks (most likely micaschist) or sands derived from river banks, in which some layers are full of mica. The biotite is often oxidised-limonitised if the firing took place at high temperatures and in an oxidising atmosphere. Due to the excellent cleavage and flaky shape of micas, if the tempering material was crushed, the grain size of micas should show a smaller range than the grain size of micas in the original rock. Carbonate grains are common components in ceramics but in some cases they do not occur at all. The amounts of carbonate grains are highly variable (up to 40-50 volume%). These carbonate grains are primarily limestone fragments and occasionally calcitic fossils. This latter one may originate from the clay as well. If the fossils are not broken, they may have derived from the clay in which fossils are occasionally scattered. In many cases, the sizes of carbonate clasts are larger and less rounded than other clasts (see Dressel 6B amphoras; JÓZSA et al., 1994). It is highly likely that, crushing carbonate to a reasonable size and portioning these carbonate grains to the raw materials were empirically tested because, in some cases, the amounts of the carbonate material depends on the part of the ceramics studied. For example, handle and rim fragments from amphoras contain more carbonate grains than the other parts of these ceramics. Therefore, 78