Colored glasses and glazes from the European bronze age to the early modern : technological developments of glass processing in four examples
The present study focuses on technological developments in the history of glass technology. I selected four aspects of glass manufacture from different periods, beginning in the earliest period of artificial glass and ending in the Early Modern time. The technology of glass manufacture was investigated by analysis of archaeological glass samples and the reproduction of used materials. The experimental approach enabled a detailed understanding of the challenges and specifications during the manufacture. In a first study, the formation of potential borosilicate layers on Mycenaean LBA relief fragments, that have been found close to gold sheet, were studied. We could demonstrate by infrared reflection spectroscopy that both borate contamination on gold and borax powder interact with the glass surface at temperatures above 800 ◦C. I suggested three mechanisms for potential borate contamination, that is by alteration of the gold sheet, the glass surface or the usage borax as a solder. The second study analyses the opacification process of Roman mosaic tesserae by the calcium antimonates CaSb2O6 and Ca2Sb2O7, and demonstrates that the in-situ crystallization at temperatures below 1200 ◦C produces the most reliable opacification. We reproduced the process in an experimental archaeological glass furnace at temperatures around 1050 ◦C. In a third study, I analyzed a selection of a Medieval glass feature from Münster, Germany, by X-ray fluorescence and optical spectroscopy. I demonstrate that the glass samples were made by at least three recipes. The fourth study focuses on the scattering properties of Cu2O and Cu0 particles with different sizes. I show by simulation of the Mie backscattering and absorption cross sections, how the optical spectra change depending on the particle size and the wavelength of light. Comparison with two late medieval / early modern sample sets from Glashütten, Germany and Wieda, Germany and fitting the backscattering curves into the UV/Vis/NIR reflectance spectra yielded an average Cu0 particle radius of 60 nm to 95 nm. The results were confirmed by SEM microscopy.