Alterations to the usual glass production process, such as putting the material under stress, can introduce effects that linger even after the material hardens. While manufacturers have long exploited this phenomenon to strengthen glass, a new theory aims to get closer to understanding why it happens.
Glass is not as well understood as most materials, because it straddles the line between liquid and solid. In typical crystalline materials, molecules assemble into a set structure over the span of the entire material as the substance solidifies from a disordered liquid form. Glass, on the other hand, retains a liquid-like disorder even after it hardens.
Without a set architecture, these disordered molecules are particularly vulnerable to outside forces. If you push or pull on a substance, you create internal forces, or stress, in the material itself. Once you remove that force, you’d expect the molecules to return to equilibrium, removing the stresses. But glassy materials “remember” the long-gone force.
Oh, look! It’s one of mine…