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

the carbonates cannot be frequently used in identifying ceramics. It is for this reason that, if possible, it is advisable to "sample" ceramics at the same part of the vessel. The absence of the carbonate material in certain ceramics can be explained by firing at a high temperature. X-ray diffraction and a careful textural-structural study of the thin sections are needed to prove this point. The occurrence of fine grained material in a thin layer on the wall of hollows in ceramics is indicative of high temperature firing. Originally these hollows were filled by carbonates. Generally the sizes of these hollows differ from the those of other pores in the ceramics. A late, secondary type of carbonate also exists. Since ceramics were covered by soils for a long time and carbon-dioxide rich fluids had percolated through them, precipitations of carbonate minerals formed on the walls of the pores in ceramics. Evidence for the presence of this type of the carbonate minerals may be observed with great certainty by using a cathodic luminescence microscope. Quartzite is a very common clast in the ceramics. The amounts of quartzite vary from trace until 15-20 volume%. There are two main types of quartzite: coarse quartzite and "microquartzite". Coarse quartzite (actually polyquartz) shows obvious metamorphic origins. Microquartzite (chert) sometimes is indicative of schistosity or a foliated texture. Microquartzite may be related to limestone in origins. Generally speaking, quartzite grains, similarly to carbonates, are not useful in identifying ceramics. However, the original locality of some Bronze Age pottery of Moncin ceramics in Aragon (north-eastern Spain), which have characteristic fibrous radial chert, could be identified mostly on the basis of these features (GERRARD 1991). Siliceous (opalic) fossils, which occur mainly in the form of siliceous sponge spicules, are characteristic of the Neolithic potsherds from Bicske-Galagonyás (SZAKMÁNY, 1996). Based on this clast, we were able to hypothetically identify the source of raw materials used in making these ceramics. We have also found a few other siliceous fossils, probably siliceous sponge spicula or radiolaria, in the ceramics, thus it can be concluded that the presence of this clast is general. However, with the exception of a few cases, they are of little importance in our studies. Accessories occur but very rarely in ceramics, and sometimes their grains are of very small in size. The quantity (and therefore importance) of accessories could increase if the tempering material was not sand or sandstone but some other substance, containing great amounts of heavy minerals. Among the accessories in ceramics, heavy minerals such as pyroxene and amphibole can be significant. For example, some Hispanic amphoras contain relatively large and numerous clinopyroxene crystals (JÓZSA and SZAKMÁNY, 1987). Also, zoisite-clinozoisite is widely spread in the Dresse! 6B amphoras (JÓZSA et al. 1994). Additional accessories frequently occurring in ceramics include: tourmaline, garnet, zircon, rutile, epidote, sphene, chlorite and opaque minerals (e.g., magnetite). It is suggested that all these minerals be identified and determined, because they together offer useful information concerning the source rocks used in ceramics. Electron microprobe analyses provide a more exact and precise identification of the accessories than micromineralogical (heavy mineral) studies. This latter technique also requires major quantities of ceramic material. Igneous and metamorphic rock fragments are not common constituents of ceramics. Usually, the grain size of these clasts in ceramics is small. It is smaller or close to the grain size of rock forming minerals in the majority of the igneous and metamorphic rocks. Therefore, these materials are present as mineral fragments derived either from clastic sediments or by the crushing of tempering materials. To identify and determine these 79