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The paper presents a set of glass fragments excavated at several different locations within and outside the late Roman fortified imperial residence Felix Romuliana (Gamzigrad, Serbia). This small group of eighteen fragments and mosaic glass tesserae are distinguished by their cobalt blue colour. The majority of the finds are mosaic tesserae (six pcs) and sheets of glass (five pcs), which could be related to architectural decoration (sectilia panels). Others are pieces left behind from secondary glass working (four pcs). There are also two fragments tentatively identified as window pane pieces, and only one find is a vessel sherd. The materials are dated to the 4th century. Significantly, some of the production debris and the two “window pane” fragments were found inside the destruction of a glass furnace. The analyses of the chemical glass composition of the finds confirmed that the blue colourant in all samples is cobalt, and antimony is also present at notable levels (except for one sample), likely to produce opacification of the glass. Regarding the origin of the raw glass, the data on almost all pieces suggests a Syro-Palestinian provenance, and a single sample could be related to Egyptian primary glass production. Importantly, the concentrations of the oxides added to the base glasses in order to modify the colour are positively correlated in certain samples, hinting at the makeup of the cobalt bearing ingredient and at a likely existence of particular production practices of the late Roman period.

Strongly coloured glass vessels decorated with marvered threads of white glass are a wide-spread and popular, but rarely studied group of high-quality glassware of medieval Islamic origin. Relatively little is known about the composition and production places of these vessels, and their chronological range is not very well defined, as many of the published finds lack contextual evidence. Here, we present detailed chemical and microstructural data on a set of well-dated purple glass vessels decorated with white threads, excavated at the Mali Grad site in Braničevo, Serbia, in an archaeological context dated to the middle/second half of the 12th century AD. The set comprises at least sixteen different vessels, manufactured from two different batches of probably Levantine plant-ash glass coloured by manganese oxide. Significantly, the results demonstrate that these batches are correlated to particular vessel shapes. The base glass of the white threads is comparable to that of the purple vessel glass, but instead of being coloured by added manganese oxide, it contains considerable amounts of tin and lead oxides which provide the effect of opacity and white colour. No difference in composition can be seen between the white glass threads used to decorate the vessels from the two different manganese-coloured batches, thus indicating a likely common production origin of the whole set. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. 177021: Urbanization Processes and Development of Medieval Society]