Trivia Junction

A Compendium of trivia I find interesting
...for the curious

About tempered glass

Tempered glass, and the tempering process creates a stress pattern that is visible within the glass.

To temper glass, it is heated to 1,200 degrees F, and then the outer surface of the glass is cooled rapidly by blowing air over it. The center of the glass cools more gradually. As it cools, it contracts, compressing the outer surfaces of the glass together and creating a stress pattern along the midplane of the glass.

Tempered glass is stronger than regular glass, but when it does break, the internal stress causes the glass to shatter into many small pieces. Since it would be dangerous if a stone shattered the windshield while someone was driving, the windshield is made from laminated safety glass.

Some upscale auto manufacturers offer laminated safety glass in side windows for added occupant safety and break-in resistance.

Laminated safety glass consists of two sheets of non-tempered glass sandwiched together with a sheet of vinyl in the middle, to which the glass adheres when it breaks. Windows made from laminated safety glass lack the grid of circles characteristic of windows made from tempered glass.

The rear windows of certain cars with window tints definitely have a more noticeable grid pattern. It is possible that the plastic tinted layer has some pattern associated with it, but it is more likely that the tint acts like polarized sun glasses to block out some of the scattered light, making it easier to discern the stress pattern in the tempered glass.

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