Application example: Glass recycling in the 11th century C.E.

Archaeological artefacts made from glass are often preserved in larger numbers and in better condition than those from more delicate organic materials such as textiles, wood, or paper. They are a valuable source for statistical information on distribution, usage, and fabrication techniques of such objects in ancient times.

A study on byzantine glass bracelets from Nufăru (in today’s Romania) has brought interesting insights on techniques of glass production: The chemical composition of numerous glass bracelet fragments of different decorative styles was determined by means of the ion beam analysis methods PIXE and PIGE (proton-induced X-ray and Gamma emission, resp.). Based on their archaeological context the bracelets had been dated to the 10th to 13th centuries C.E. In this period techniques of glass production underwent significant changes and artisans experimented vividly: they tried various pigments for colouring the glasses and transitioned from natron to certain regionally available plant ashes as fluxes. The majority of the glass fragments from Nufăru turned out to contain both kind of fluxes. Since only one flux is used when a glass is initially prepared, this finding indicates strongly that Nufăru artisans routinely melted down glasses of different production processed, mixed the melts and formed them into new glasswares. The detected pigments lead to the same conclusion: A blue colouring is achieved with either copper- or cobalt-based pigments; a mixture of both is unnecessary. Still, some blue glass from Nufăru contains both types of pigments, indicating that glass fragments were sorted by colour and recycled by melting them down together.

Glass bracelets are a popular adornment since many centuries and in many regions. Findings from physical investigations of these objects complement their art historic assessment in a meaningful way. They show that the the byzantine settlement in Nufăru was at a crossroads in time and space for the production techniques of coloured glass.

• R. Bugoi et al., Investigations of Byzantine glass bracelets from Nufăru, Romania, using external PIXE-PIGE methods.
  Journal of Archaeological Science 40 (2013) 2881
  https://doi.org/10.1016/j.jas.2013.03.003