have you had to explain to customers what quench marks are.

If I knew what one was, it'd be a start.

The patterns you see in tempered glass caused by the air jets that cool the glass. Mainly visable with polarized sunglasses. Alot of camaro back glass were replace because of them back in the day. They are an inherent part of every tempered glass.

I just learned my new thing for the day!! LOL!!

Yeah it's a new one to me too, and I'm in the customer complaint department LOL, so now I'll be armed with valuable information if anyone calls and complains about a tempered AG glass part or IG unit.

I was under the impression that it was more from the mold, than the quenching. Usually only on curved parts, seldom noticed on flat.

I remember some years back Ford had a problem with a Tbird backglass, if I recall correctly, that Ford was particularly proud of because of a multiple compound curve in the glass for the new body style. They warranted a bunch of them before issuing a memo to dealers that stated 'We're sorry, but we can't change the laws of physics' type of explanation for the customer. We changed a few for Ford, with a written explanation to the customer that the replacement would likely be the same as the one they wanted removed.

Usually with the polarized sunglasses, yes, but high humidity brings it out even worse, like right after a spring rain or car wash when the customer is in the sun before anything has a chance to dry.

One customer didn't believe what Ford was telling him, and was pretty determined to get another backglass. I confirmed Ford's statement, and noted that he wasn't charged any extra for the geometric pattern in the glass. lol

You may be right about that. I was just given the other explanation years ago from a PPG factory rep. I understand that there are guys that can tell you which plant it was made at by looking at the quench mark patterns.