There is no change in the crack system of glass, no matter its various forms.

That was the heart of the message delivered by both Sebastian Schula and Jens Schneider during a technical session today at the Glass Performance Days Conference in Tampere, Finland. To further their point, the two German glass experts employed tests to better showcase the indentation crack initiation mechanisms and characterization of the scratch visibility of glass, comparing the scratch visibility of annealed, tempered and chemical-strengthened glass.

Schula and Schneider say they proved the crack system the different glass types is generally identical. The lateral crack width for the annealed glass and the tempered glasses (heat-strengthened glass and fully-tempered glass) was comparable (within the range of 150 µm to 175 µm). Contrary, chemical strengthened glasses (soda-lime-silicate and aluminosilicate glass) showed considerable smaller lateral crack widths within the range of 50 µm, meaning that scratches on annealed and tempered glasses are more macroscopic visible than on the chemical strengthened glasses and sapphire crystal.

Cambridge University professor Caroline Butchart also addressed the gathering of industry insiders, speaking about the influence of moisture on the post-fracture performance of laminated glass.

Butchart showed that – in the presence of water – the adhesion between the glass and interlayer was less than half that observed in dry conditions. As a result, she said, full-scale destructive testing should be performed under wet rather than ambient conditions for exposed glazing. Future methods developed to determine the post-fracture performance of laminated glass should distinguish between internal and external laminated glass. Alternatively, laminated glass constructed of three or more layers of glass could be used to protect the interlayer from water ingress, she said.

Stay tuned to for more from the event throughout the week.