Analyzing The Optical Anisotropy Effects Within the Tempered Architectural Glass by Digital Image Processing

The analysis of the retardation images and the evaluation of the anisotropy quality of the glass are of great interest to detect and sort out very low-quality glass panes directly in the production process.

FREMONT, CA: For its high strength and resilience to thermal stress, thermally toughened glass is frequently employed in visually ambitious buildings. Owing to boundary conditions that are connected to technology, economy, and safety, only thermally toughened glass may be used to reach the glass dimensions needed for high-quality facade projects (fracture behavior). However, this type of glass can produce optical phenomena that the observer can find unsettling. Under specific light incidence, weather, and daytime conditions, the so-called anisotropies or iridescence can be seen as a distinctive pattern on the façade in the shape of grey, white, or rainbow-coloured spots, rings, or stripes. The production of glass panes and how polarised light affects human vision are the root causes of these phenomena. The thermal tempering of glass is a well-known technique that involves heating the base glass in a tempering furnace to a temperature that is approximately 100K above the glass transition temperature, followed by a quick cooling step using air quenching. Remaining tensions are created as a result, which is typical of glass that has undergone thermal toughening. Heat transfer and glass support have an impact on the widely used horizontal tempering technique. When the glass is heated and cooled, local temperature gradients can lead to variations in the primary stresses. The optical characteristics of the glass might change even with minor variations. A birefringent medium with direction-dependent optical (anisotropic) qualities develops from an otherwise optically isotropic medium. Although undesired, anisotropy effects are not regarded as flaws or inadequacies.

The photoelasticity can be used to explain the coloured iridescence effects. A polarised light beam splits into two directions parallel to the main strains when it enters a flat glass. The two