Historically, flat glass production was a handcrafted process, resulting in glass elements with optical imperfections that altered the clarity of the view through windows – this is a decisive aesthetic feature today. In contrast, modern glass used in building industry is predominantly produced through float glass process. Since its development in the 1960s, it enabled the mass
production of fully transparent glass free of irregularities. Thereby, traditional flat glass production methods, such as cylinder-blowing or rolled-glass processes, were displaced to both economic and quality improvements.
However, with the discontinuation of older methods, the authenticity of historical buildings was also diminished.
To preserve authenticity, contemporary projects aim to incorporate glass produced using traditional techniques, embracing the inherent optical irregularities of hand-crafted-glass. One challenge is that mouth-blown-glass lacks standardization in terms of product specifications, with no established values for geometric tolerances or loadbearing capacity. The primary objective of the presented research is to characterize the load-bearing capacity of contemporary produced mouth-blown-glass in comparison with float glass. Additionally, the study explores the effects of thermal toughening on mouth-blown glass. The research involves geometrical and photoelastic analysis of 60 specimens mouth-blown-glass with 2 mm thickness. Afterwards, the four-point-bending-test (EN1288-3) is adapted to test specimens with 2 mm thickness and to evaluate the load-bearing capacity and fracture pattern of mouth-blown glass. The specimens were produced in 2024 using the traditional cylinder-blowing-method. The results of the study confirm and quantify significant thickness tolerances in mouth-blown-glass. But, the results also demonstrate considerable potentials for the use of mouth-blown-glass in building industry. The load-bearing capacity of modern mouth-blown-glass was found to be comparable to annealed and thermally toughened glass.
Furthermore, the fracture pattern of mouth-blown-glass, depending on thickness, corresponds to thermally toughened glass. The paper also discusses the importance of considering thickness tolerances when estimating realistic glass strength values.