Chemical Strengthening of Glass: After more than 70 years of research, glasses can now be made strong enough to be bent sharply.

Although man has known for centuries that glass had potentially large mechanical capabilities, he had been content, until rather recently, to accept the fragility of bulk glass. Annealing, the first step in making glass a useful material, enabled him to make articles with strengths adequate for satisfactory service. Physical tempering provided the next big advance, permitting strengths more than three times those of annealed glass in simple shapes. Today, chemical strengthening is a real possibility for producing glass articles, regardless of design, more than three times the strength of physically tempered ware.