Ilon Gábor szerk.: Pápai Múzeumi Értesítő 1. (Pápa, 1988)
VARGA István - SÜVEGH Gábor - NAGYNÉ CZAKÓ Ilona: Egy későbronzkori kerámia komplett vizsgálata
Complex study of a ceramics from the late Bronze age Lots of ceramics and ceramic fragments have been found at the late Bronze age site of Németbánya .Their colour was mostly black, except some of them which ha a red, reddishbrown or rarely a light gray colour, The studied specimen originated feom 43-118 cm depth of the "G" profile. Both the inner and outer surfaces of the specimen were smo oth as a glass graphitic black. The color of lits fracture plane was also black, but under the outer surface a reddish-brown continous belt of 1 mm thickness has been observed. The vessel s wall thickness was only 7 mm, and had a leaning out rim. It must have been used frequently, because marks of wear could have been seen on it. Despite the fact that the material of the specimen was not very hard, traces of corrosion were not observed. One of the goals of this study was to decide the element creating the colour of the ceramics. Laser emission measurement 5 proved that the distribution of the elements in the specimen was perfectly homogeneous, i.e. the colour difference between the reddish-brovn and black phase can not be explained by their difference in composition.Besides, mangane- * se in higher concentration could not be identified in the specimen, so the black colour was not produced by some manganesecompound. This assumption was supported by the results of neutronactivation analysis identifying 512 ppm Mn in the studied ceramics. The dissolution of pulverized ceramics was attempted in the mixture of Hh and HC10». Undissolved small black grains suggest the presence of graphite or carbon. Since on the DTA curve H of the specimen exotermic peak did not show up above 700*C, the presence of graphite can be excluded.In our opinion the black colour of the ceramics was produced by amorphous carbon. Recently György Duma have investigated the incorporation of carbon into ceramics? He has found that the 2 CO C0 X + C reaction taking place mostly in reducing atmosphere may cause the precipitation of carbon, which has a maximum about 500 "c. The reaction takes place in the temperature of 300 - 700 "C, above 700 'c the equilibrium is shifted completely towarda the formation of CO. The presence of carbon in the specimen proves that the ceramics was fired between 300 and 700 "c. This is supported by the Röntgen-diffraction pattern* of the sample, i.e. clay mineral of illite type was identified, whose lattice should have been destroyed above 700 'C* Usually the incorporation of carbon occurs in a few cm depth from the surface, because dur to the rather big size of the CO molecule, its penatration depth is limited. The penetration range of the CO depends on the pressure of the firing atmosphere, but it is primarily determined by the pore-size of the ceramics. The black colour of the fracture of the ceramics suggests that the sizes of pores were quite large. I A few experiments were carried out to study the effect of carbon incorporation into the ceramics. Two specimens of a clay were fired at 300 - 400'C for the same time, but one of them was embedded in carbon powder to ensure the reducing circumstances. The firing at such a low temperature was incomplete, so the ceramics produced under oxidizing circumstances could be easily crumbled. However the other specimen formed in reducing condition could not be crumbled even after having kept in water for several days.This experimental fact can be explained by the improved hydrophobity of the ceramics due to the incorporation of carbon. The DTA curve of ceramics sample from Németbánya proves that low carbon content can not provide suitable protection against durable influences, that is the sample strongly rehydrated when buried. In the case of graphitic ceramics some favorable effect of the graphite can only be excepted above bh graphite content. 8 The thin section of the studied ceramics 5 showed high silica content of metamorphic origin, and the presence of illite and limonite in large quantity. Opaque grains could „ be seen in it, that were probably some iron-oxide particles. Beside, a small amount of altered biotite and muscovite as well tourmaline, zircon and epidote were found.
