The development of toughened glass dates back to the mid-17th century. One of the Rhine princes, Robert, who had done an interesting experiment, put a drop of molten glass in cold water and made a Very hard glass. This high-strength granular glass is like a drop of water with a long, curved tail called "Prince Robert". However, when the tail of the pellet is bent and broken, it is surprising that the whole pellet therefore suddenly and violently collapses, and even becomes a fine powder. This practice, much like metal quenching, which is quenching glass. This quenching does not make any change in the composition of the glass, so it is also called physical quenching (physical tempered), so tempered glass called tempered glass, also known as quenched glass.
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