9110/9130
Transparent Beech Vase is a prototype developed as part of the ongoing 9110/9130 research project, investigating historic forest glassworks across Western Pomerania, with a particular focus on the present-day Polish–German borderland and the Ueckermünde Heath.
Glass blown into the plaster mold.
Photos: Mila Łapko
The 9110/9130 research project takes its name from two European Union Natura 2000 habitat codes used to classify beech forests occurring in Western Pomerania: 9110, Luzulo-Fagetum beech forests, corresponding to acidic beech forests, and 9130, Asperulo-Fagetum beech forests, corresponding to nutrient-rich beech forests. Both habitat types are documented in the Polish–German borderland, including the Ueckermünde Heath.
Their primary product was Forest Glass (Waldglas), characteristic of Central Europe. Its greenish hue resulted mainly from iron compounds naturally present in quartz sand and other raw materials used in the glass batch (Wedepohl & Simon, 2010; Stern & Gerber, 2004). A key ingredient was potash (potassium carbonate), obtained by leaching wood ash. Acting as a flux, potash lowered the melting temperature of the glass batch and was therefore essential to forest glassmaking (Cílová & Woitsch, 2012).
Across Central Europe, potash was produced from the ash of various tree species and ferns. From the sixteenth and seventeenth centuries onward, however, European beech (Fagus sylvatica) became an important and highly valued source. Beech ash yielded substantial amounts of potassium, while purified potash provided a cleaner and more predictable chemical composition, allowing greater control over the glass batch (Wedepohl, 2007; Wedepohl & Simon, 2010; Cílová & Woitsch, 2012).
Source: Ralf Wendt, Das Waldglas. Volkskundliche Sammlungen. Bauernkultur in Mecklenburg. Band IV, Schwerin, Historisches Museum, 1977.
Beech, potash and Making of Transparency
The development of purified potash was one of the technological advances that enabled the production of high-quality potash-lime glass. Potash itself did not make glass colourless; rather, as a purer and more predictable flux, it allowed greater control over the glass recipe. Combined with high-purity quartz sand, lime and carefully controlled firing conditions, it contributed to the production of nearly colourless glass, referred to in historical sources as crystal glass or chalk glass (Cílová et al., 2020; Stern & Gerber, 2004).
Glass colour was also influenced by manganese. In some regions manganese occurred naturally in the raw materials, while elsewhere it was deliberately introduced as a decolourising agent (Glasmacherseife). Manganese oxide could counteract the green tint caused by iron compounds, allowing clearer glass to be produced (Stern & Gerber, 2004; Cílová et al., 2020). The technological range of the Stolzenburg glasshouse is reflected in its nineteenth-century production of white (weisse), green (grüne) and brown (braune) glass (Humbsch, 2004).
Glassmaking consumed enormous quantities of timber. Wood served simultaneously as fuel and as the raw material for producing potash. The depletion of nearby timber resources could therefore bring a glasshouse to an end, as happened at Neu Rothemühl, where the glasshouse was closed in 1768 because the wood required for production had become scarce.
The Forest After Glass
Today, many forests across Western Pomerania are dominated by pine, yet their historical composition was more diverse. Research by Mareike Radtke and colleagues on north-eastern Germany—a region adjacent to Western Pomerania with a comparable environmental history—shows that by the late eighteenth century beech accounted for around 40% of tree cover, pine for approximately 36%, while oak also formed a substantial component. Over the following two centuries, forestry practices dramatically increased the dominance of pine, while the share of beech and oak declined. Although the study does not focus directly on Western Pomerania, it documents landscape transformations relevant to the wider region (Radtke et al., 2017).
The 9110/9130 project approaches Western Pomerania through the relationship between geology, forest and glassmaking. The geological mosaic made different mineral resources available within the same region; the resulting diversity of soils supported different forest communities; and the forest supplied both fuel and the chemical raw material needed to produce potash. Transparency was therefore not simply an achievement of the glass furnace. It emerged from the convergence of geological resources, forest composition, material knowledge and glassmaking technology.