X-ray diffractometric and electron microprobe study of the Avar Age glass beads
Basic data for the genetics of glass beads II.
Red opaque glasses

 I. Fórizs, M. Tóth, G. Nagy, A. Pásztor

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Red opaque glass beads chosen on typological basis from the Early Avar Age (6^th-7^th centuries A.D.), excavated in Budakalász and Szegvár-Sápoldal cemeteries (Hungary) were studied by means of X-ray diffractometry and electron microprobe, and the results are evaluated. Our previous recognition (FÓRIZS et al. 1996), that a special technology/method was used for coloring these red beads, inspired us to do a detailed study on red opaque glass beads. In the literature we only found HENDERSON (1988b) to recognize this technology beyond us.

According to the chemical composition of the studied beads their base glass belongs to two classical glass types: 6 beads are Roman type (made from soda:limestone:sand), 3 beads are Mesopotamian types (made from halophytic plant ash:limestone:sand), see Table 2 and Figs. 13, 14 & 15. We may draw a further conclusion from the chemical compositions: the three raw materials were used by the same ratio in both glass type, i.e. the same recipe was used. Beads of both glass types can be found in Budakalász and Szegvár-Sápoldal, so regarding the base glass types there is no difference between the two localities.

The authors showed that for getting the red color iron was deliberately added to the beads beside the traditional colorant (Cu) and modifiers (Pb, Sn) at both localities. The amount of the added iron significantly differs at the two localities (Table 2, Figs. 17 & 18), and from this fact it is inferred that the two sets of beads are products of different workshops.

From the types of inclusions identified in the glass beads we may conclude that the copper was added to the glass in metal form (Fig. 10), while the iron was added in the form of metal turnings and/or in the form of an iron-oxide (e.g. bog ore) (Fig. 7).

Based on geochemical data it is most likely that in the case of glasses containing ³3 w% iron (as Fe₂O₃) the iron was deliberately added, while when the iron content is <2 w% the iron is natural contaminant of the raw materials. From the data for red opaque glasses found in the literature and arranged according this above supposition (Table 4, Fig.19) we may conclude that red opaque glass objects colored by copper+iron first occurred on the Hurritan territory (Nuzi, before 1400 BC), then in Persia (Persepolis 5^th c. BC) and India (Kauzambi, 2^nd c. BC - 2^nd c. A.D.). Later on they occurred in Byzantine (Constantinople, 6^th c. A.D.), in the Carpathian Basin (3^rd-7^th c. A.D.), in The Netherlands (6^th-7^th c. A.D.), in Viking Land (8^th c. A.D.), in Ireland (6^th-10^th c. A.D.) and in Kiev (11^th c. A.D.). This technology of combination of copper and iron as colorants in the red glasses most probably was invented in the "Orient" and came through the Byzantine and/or Eastern Europe to the Carpathian Basin and then furtherward to the Northern Europe. Inferable the spreading of this technology was along ancient trading routes or by migration of peoples.

Because of the proximity in time and space we have compared the chemical compositions of our beads with those excavated in Borovce (Slovakia, 8^th-10^th c. A.D., STASSÍKOVÁ-STUKOVSKÁ & PLSKO 1997) in spite they did not analyze red opaque glasses, however remnants of glass workshop were unearthed recently nearby Bratislava (not far away from Borovce; unpublished, STASSÍKOVÁ-STUKOVSKÁ per. com. 1998). So one hypothetical provenance of our beads may be the above workshop and this supposition is more-or-less supported by the base glass types found in Borovce. In this question crucial will be the serving period of this workshop and the chemical composition of red glasses.

The chemical composition of 6^th-7^th century red opaque glasses excavated in Maastricht (The Netherlands, SABLEROLLES et al. 1997) from a waste pit related to the production of glass beads are very similar to one group of glass beads from Budakalász, i.e. to those of Roman base glass type and with high lead content (B-2, B-11 in Table 2). Even the iron contents are very close to each other (in average: 3.8 w% in Maastricht, 4.30 w% in Budakalász).

Glass objects from Rhineland studied by X-ray fluorescent analysis by HOFFMANN (1994) have close typological and typochronological relation to the glass beads of Budakalász and Szegvár-Sápoldal. Hoffmann's results indicate that the surface of the beads he studied were more-or-less weathered, so his published chemical data can not be compared to our results directly, because his data are not related to the original glass, but to a partly weathered glass. However his results foreshadow that the red glasses from Rhineland were colored by copper+iron together, although a definite statement can be said only on the basis of analyses made on unweathered (freshly cut, see COX & POLLARD 1977) surface of beads.

Summarizing our results: red opaque glass beads from the 6^th-7^th c. A.D. excavated in Budakalász and Szegvár-Sápoldal cemeteries (Hungary) were colored by a special method, the combination of copper and iron. This method most likely originates from Asia and glass beads made by this method can already be found among the Sarmatian glass objects from the 3^rd-4^th c. A.D. in the Carpathian Basin (FLÓRIÁN & ZIMMER 1980a,b). The measured chemical compositions show close relation to those excavated in Borovce (Slovakia) and in Maastricht (The Netherlands). Latter localities hypothetically may be production sites of some of the investigated glass beads, however there are many areas where the glass objects are typologically closely related to our ones and no analytical investigation have been carried out on these glasses up to now. Definite statement on the provenance of our Avar Age glass beads can only be formulated after completion of these investigations.