Glass is one of the oldest materials created by humans, dating back to about 4,000 years ago, when craftsmen working in Mesopotamia, the land between the Tigris and Euphrates Rivers, discovered the art of mixing sand, soda, and lime to make glass.
[3] In 1913 Günther Schulze was the first to study the diffusion of silver ions into the glass using silver nitrate salt (AgNO3) as ion source, starting a whole series of studies aimed to understand the chemical and physical nature of the phenomenon and its effects on some physical properties of the glass so treated.
S. Donald Stookey started research into using it for strengthening by June 1960,[6] and the topic was discussed at a symposium in Florence in September 1961,[7] but it was Steven Kistler[8] and, independently, Paul Henri Acloque and Jean Paul Tochon of Saint-Gobain who managed to improve the compressive strength threefold in 1962.
[6] Replacement of smaller sodium ions (Na+) with larger potassium ones (K+) in the pristine glass matrix was able to prevent or heal over the possible formation of micro/nano-cracks on the specimen surface, increasing its mechanical strength.
This replacement of ions causes the surface of the glass to be in a state of compression and the core in compensating tension.
Since phones are commonly carried in a pocket or purse with items such as keys, scratch resistance is important.
However, the process does not use extreme variations of temperature and therefore chemically strengthened glass has little or no bow or warp, optical distortion, or strain pattern.
Similarly, when the surface of chemically strengthened glass is deeply scratched, this area loses its additional strength.