Hadak Útján. A népvándorlás kor fiatal kutatóinak konferenciája (Szeged, 2000)

Fórizs István - Pásztor Adrien - Nagy Géza - Tóth Mária: Avar kori üveggyöngyök röntgendiffrakciós és elektron-mikroszondás vizsgálata. Alapadatok az üveggyöngyök genetikájához IV. Miből és hogyan?

FÓR1ZS István - PÁSZTOR Adrien - NAGY Géza - TÓTH Mária

may come from the other two main components of the glass: minor elements of sand and limestone), on the other hand it brings up the possibility that there are mixed type glasses. This latter type is born when a broken glass artifact is used for making new artifacts and the type of newly used raw material differs from that used for the broken one. In this case the content of all the three components of MgO, K20 and P2Os must be in a transition position. In the case of the above mentioned three samples it is true, although the phosphate content of samples SlOa and B27 is high enough for Mesopotamian type.

The published phosphate content of Mesopotamian glasses ranges between 0.20% and 0.50% (BRILL 1970;

VERJTÁ 1995; WEDEPOHL ET AL. 1997). The phosphate content of our four samples (S9, SI Ob, T6, Ti2, see Table 1) is considerable higher, it ranges between 1.0% and 1.6%. One may think that the alkali:(sand+limestone) ratio in the case of these beads were far higher than usually, but this case the Ca and Na content should be increased with phosphorus. The CaO content really shows positive correlation with P205 content (Fig. 4. 1), but the Na20 content does not (Fig.

4. 2). This points to the possibility that the used plant ash was not the well known Syrian one, but an other one, even a local source in the Carpathian Basin cannot be excluded.

DISTRIBUTION OF BASE GLASS TYPES IN EUROPE IN THE FIRST MILLENNIUM A.D.

Sporadic data allow us to create only an incomplete, but a very interesting picture on the distribution of the Roman and Mesopotamian type glasses in Europe.

Only Roman type glasses were found: in Brittany (1st millennium, SANDERSON ET AL. 1984), in Maastricht (The Netherlands, 6th-7lh c., SABLEROLLES et al. 1997), in France (Gallo-Roman times, VELDE-GENDRON 1980), in Germany (Roman, Merovingian and Karolingian times until the 9th c., WEDEPOHL ET AL. 1997). Both types were found: in Northern Poland (lst-5th c., STAWIARSKA 1984), in Slovakia (Borovce, 7th—11th c., staSSíkovA-StukovskA-plSko 1997), in Hungary (Zalakomár (7th-9th c., DEKÓWNA 1989; Környe, 6,h-8,h

c., SALAMON ET AL. 1977; Budakalász, Szegvár-Sápoldal, Szentendre, Tiszaföldvár, Tiszavasvári, 4 -7th c., this work), Ukraine (Saltovo, 8d,-9lh c., BEZBORODOV 1969), Russia (Preslav, 9th— 10th c., Staraya Ladoga, 7th-8th c., BEZBORODOV 1969), Germany (after 800 A.D., WEDEPOHL ET AL. 1997).

Summarizing: Roman type glasses in the first Millennium were widespread all over Europe, while the Mesopotamian type glasses appeared in Central and Eastern Europe. This observation indirectly indicates that the technology of studied Avar Age glasses in Hungary have oriental origin or some of the raw material originated from the Orient.

CRYSTALLINE INCLUSIONS

Opaque glasses contain a lot of inclusions, which is not characteristic for transparent and translucid glasses. Crystalline inclusions (morphology, chemical composition, etc.) gives a lot of information about the used raw materials and applied technology. The studied red opaque beads contain a lot of iron-bearing inclusions and their glass matrix has a rather high Fe content indicating that iron was deliberately added to the glass. The oxidation state of the iron in the inclusions varies from reduced state (metal) to the totally oxidized state (Fig. 5. 1-2). The morphology of some of these inclusions resembles to metal turnings (Fig. 5. 2). From these observations we may infer that iron was added in the form of metal turnings, and its role was an internal reducer. We suppose that a two stage technology was applied for making the studied opaque red beads. First stage: making the base glass (frit), second stage: the powdered base glass was mixed with the powdered additives and/or turnings of metal (e.g. iron, copper) and this mixture was very carefully heated up to the point when the powdered frit was molten, but a part of the iron remained in reduced state. After the bead was formed, it was cooled down very slowly in reduced atmospheric conditions (e.g. in the closed kiln), and the reduced state iron helped the precipitation of tiny copper ruby crystals. Latter give a bright red color which is modified by the glass matrix and the result is a brick red color.

It is interesting to have a look on the map showing the places where the excavated red opaque glass was colored by copper or a combination of copper and iron (Fig. 6). The

oldest glasses colored with Cu+Fe were found in the territory of the Hurritan Empire (1400 BC), then it emerged in India (2nd c. BC - 5th c. A.D.), later on in Byzantine (6th c. A.D.), in the Carpathian Basin (3rd-7th c.), and at last in the Netherlands (6u’-7lh c.), in Viking land (811' c.) and Ireland (6th—10th c.). This outline a long rout from India to Northern Europe incorporating many of the most important inland Eurasian merchant routs.

Few relict metal copper inclusions (Fig. 5. 3) were found in the opaque red and blue beads indicating that also copper was added in the form of metal turnings.

Opaque yellow beads are colored by (Pb, Sn)-oxide grains and their glass matrix is very Pb-rich and homogeneous at the same time. Veritá (VERITÁ 1995) refers to a Medieval Venetian glass recipe for making opaque yellow. This recipe describes a two stage technology (see above for red opaque), which explains why the glass matrix is homogeneous when the inclusion is very Pb-rich.

Opaque white beads contain a lot of Sn02 inclusions with size of 1-20 micrometer (Fig. 5. 4). In some beads there are few big (50-100 pm) Sn02 inclusions containing a considerable amount of Pb (Fig. 5. 5). The Venetian recipe cited by Veritá (VERITA 1995) described a way for making opaque white glass (enamel) when the same (Pb, Sn)-oxide was used as that for yellow opaque glass with the difference, that lead-silicate frit was used for opaque yellow and lead-free soda-lime-silicate frit for opaque white. Most probably a few of the studied Avar Age white beads were made in this way.

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