S5006694

208 Halina Dobrzańska and Jan Piekarczyk

Additionaliy. for comparatiye analytical purposes łhe results of examlnlng a modem flne grey wheel-thrown jug Is presenled. It was experimentally mada fbllowing tha composltlon of cłay used in fhe thlrd century AD at Haarhausen. Kr. Amstadt (Thuringia) (Dobrzańska, Piekarczyk 1999-2000: 97).

Testing method

Ultrasonic testing of materials and objects is based on measuring the velocity of wave propagation in elastlc bodies. Velocity is a funćtlon of microstructure, elastic constants, density and geometrie dimensions of an exa-mined materiał (KrautkrAmer, KrautkrAmer 1977). Ultra-sonics can be used to test objects of different shapes and sizes, age and volumes using various parameters and areas analysed. It is a non-destructive but time-consumlng method.

in the ultrasonic testing of the pottery sampled the longitudinal ultrasonic wave was transmltted through the walls of the vessel. A MT-541 (UNIPAN) device was used with a pair of transducers adjusted to point measure-ments of the frequency of 1 MHz. The velocity of the longitudinal ultrasonic wave propagation — which is the characteristic feature of any materiał — is directly pro-portional to the density of the materiał (Piekarczyk et al. 1982; Piekarczyk 1984; 1987; Piekarczyk eta/. 1999). When the ultrasonic wave is sent through adjoining areas of the sample characterised by a different materiał density, that is, of different porosity, different velocities of the ultrasonic wave are measured. The distribution of density in a sample can be determined in a non-destructive way by examining the distribution of vek>cities on its surface and thls is the premise on which ultrasonic testing of pottery rests.

In the present case, ultrasonic testing was carried out along the walls of the vessels at the points indicated on the Figures which accompany thls paper. The values of the average velocities (VL) with the standard devla-tion for each measurement point and the thlckness of the samples (d) at particular measurement points are shown In Figs. 6-10

Results of analyses

Flne grey vessel fragment from Radiowice (Figs. 1, 6)

The ultrasonic wave was directed through the ves-sel'8 base. Measurement points of the longitudinal wave propagation vek>city were selected in such a way as to

determine velocitlas on the thlckened part of the clay coil of which the pot was madę at Intermlttent points, that Is where the areas of the spiral coil bond. At the point where the spiral begins at the centra of the base where It is thlckened (point 1), high ultrasonic wave ve-loclty was recorded (v,=2700 m/s). Velocitiea of higher values (v_t ■2900 m/s) were measured at the adjacent coil in points 4 and 5 and in points 6 and 8 (Fig. 6: VL, d). Velocłty inerease can also be observed in another spiral which forms the vessel's base (point 10). Low volocitios were observed for points where the spiral coil bonds. A velocity drop was recorded In points 2, 3, 7, 9, 11 lo-cated on the bonding points of the spiral coil. The longer the distance from the centre of the vessel the thicker the coil of clay. The minimum velocity (v_L =1850 m/s) was measured at the basal ring (points 11-15).

Flne grey vessel fragment from Roszowickl Las

(Figs. 2. 7).

Ultrasonic testing was performed on a fragment of a pot consisting of part of its base and wali. The basal ring (points 7-8) is the thickest part of the tested fragment (Fig. 7: VL, d). This vessel also shows density changes demonstrated by the ultrasonic wave velocity fluctuations, which occur alternately alongside the ves-sel's base and the wali. The vessel shows considerabłe porosity throughout the clay and intemal shallow cracks alongside its wali can be detected. The shallow crack (points 1,2) causes a serious decrease of the ultrasonic wave veloclty (v_L =650 m/s). The max!mum velocity (v_L =2100 m/s) was reached on the wali in point 4 and in points 10, 11 of the vessel's base. It was observed that in the adjacent areas (points 3 and 6 of the wali and 9 and 12 of the vessel's base) the velocity drops only to rise in the further section (point 13) of the vessel’s base.

Slight corrugation of the vessel's base and convexl-ties at the areas of inereased velocitłes are ample evl-dence for the colling technique forming the base and the wali. The artefact was flred In low temperaturę, which is indicated by low yelocity values and the colour of the vessel'8 section.

Flne grey vessel fragment from Pełczyska (Figa. 3, 8)

We observe a symmetrical distribution of thlckness and partially of wave yelocity against the axis of the tested yessel'8 base. In the middle of the base (point 10) a thicke-nlng was detected as well as the maxlmum yelocity of the longitudinal ultrasonic wave propagation (v_L =2500 m/s) (Fig. 8: VL, d). In the adjoining sections the yelocity of

Flne grey vowel fragment Orewiog: E. Osipowa. Photo: B. Koteckl

Fig. 1. Radlowlce. dolnośląskie provlnoe.