Re: Windshield quality

Posted by Fish'n Jim On 2015/8/5 21:01:37

Windshield glass is safety "laminated" and has clear plastic sandwiched between two sheets of glass to prevent breakage. Over time this plastic can degrade/discolor(heat&UV) and lose strength.
Glass is also susceptible to micro stress cracking over time, so one day it's just fine and the next day it has a crack propagating on one or both sides of the laminate depending on how it was stressed.
If you wash your car on a hot sunny day and the interior/glass gets real hot and then hit windshield with a cold water spray, this will tests it's "crackability". Wash in the shade if possible or while it's still cool.
Side glass sold now is usually "tempered" which makes it shatter, break into small pieces, when it breaks for safety reasons. Shards are deadly in a crash scenario. The older wreck photos, have alot to head imprints in the windshields from being thrown through the windshield, prior to seat belts.
I believe the glass on my '49 is laminated throughout, as the edges are getting yellow, so for the early models tempered wouldn't be "correct" but safer. Not sure what year they switched.
Folklore sez DuPont had a clear overliner material that prevents glass from breaking and it was rejected for cost reasons.
I worked on some glass chemical strengthening projects in my work daze. We made hot end coatings for bottles to prevent them from breaking during packaging and recycling and the Low E flat glass.