New developments in early industrial stained glasses

In the present work, 50 samples of stained glass have been studied in order to disclose the improvements in glass production introduced after the growth of industry in the late 18th and early 19th centuries; the large scale production of glass and the development of new techniques led to a revival of stained glass manufacture, culminated during the late 19th century with the addition to the batch of many new colouring agents, or syhnthetic versions of the old ones, and synthesized raw materials (such as Solvay processed soda). The sample repertory includes both transparent and opalescent glasses produced by some Italian, German and American glassworks between the late 19th and the first half of the 20th centuries. All samples have been preliminarily analyzed by SEM-EDS and XRF in order to characterize the batch composition and the colouring agents. XRD has been utilized as well to identify crystalline phases employed as opacifying agents. Based on major element contents, the majority of samples can be considered as soda-lime-silica glasses, with few examples of mixed alkali-lime and lead-potash glasses. Concerning coloured transparent glasses, the addition of new colouring agents synthesized during the 19th century such as pure cobalt (mainly used for blue tints), cadmium (yellow and orange), selenium (pink and amber) and zinc (associated with sulphur to produce a deep red tint) has been confirmed. Moreover, high contents of calcium and fluorine have been detected in all opalescent samples by SEM-EDS and XRF (XRD analysis confirmed the presence of fluorite, CaF), while zirconium (introduced as zircon, ZrSiO4 or zirconium dioxide,ZrO2), has been detected as well in some samples.