Bizarre rear window mystery phenomenon
 

OK, somebody tell me what the hell this is...It's been bugging me for a while now. I only see it on newer cars, including mine. On the back window, you'll sometimes see what looks like a moire pattern (grid of spots) on the back window. It doesn't wash off, and you can only see it in the sunlight, and it only shows up on the rear window. WTF is it? Has anyone else seen this?

If there's a dumb obvious explanation, please be kind.

i bet it has something to do with the safety glass thingy :p

Re: Bizarre rear window mystery phenomenon
 

I can't see the spots on my sedan unless I use my polarized driving glasses, then they're visible in my car and many others on the road. I never gave this much attention until now... :D

A quick search on Google returned this:

This effect is the result of the tempering process of glass. The internal stresses in the tempered glass change the polarization of light passing through it. The glass is made that way so it crumbles when it breaks.

The manufacturers could effect more uniform methods of tempering and the result would be clear glass on all the surface. But why should they? Iit would cost more and the public accepts shoddy work as standard fare.

:)

Thanks Yellowdragon. Is there anything the Google searchbots CAN'T find?

So it's just b/c they're too cheap to make the glass right? Should have known. :mad:

I just noticed those spots recently when I got my new Oakleys. Thought it was a bit weird. I only noticed it on tinted glass.
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is it a circle? cuz they use a suction cup type deal to put the window in at the plant.

I don't know about anybody else, but I always see two red circles.
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Hi Proto2k; those might be the suction cup marks...

The circles I refer to are small and cover the whole glass in a pattern. They can only be seen at an angle or with polarizing lenses. But in very shoddy glasswork, they can be plainly seen...

OoOoh . . . Mothman Prophesies anyone? :eek:

:bat: :bat:

For me, they are seen only at a certain angle, approximately 3 feet to the right of the trunk lid.

The spots I was talking about are about an inch around, and evenly spaced over the whole window, like a "half-tone" pattern. (or, on my neighbor's Prizm, a series of vertical streaks) They kinda look like oil slicks embedded in the glass. What I can't figure out is if it's a result of the tempering process, why do I only see it on back windows?

When I first got polarized sunglasses a couple of years ago, the lady at the optometrist's office was trying to tell me how wonderful they were:

"Now you'll be able to see the stress marks in the car windows!!"

I'm not lying, that's what she said.

And she's right, but I'm not sure how wonderful a thing that is.

:confused:

I've seen them in my side windows as well.

I, too had these marks - almost looks like the window is "plaid" ;).

Interestingly, getting my windows tinted made the marks completely disappear. Maybe I'd see them again with polarized glasses, but I do not see them anymore with regular glasses or sunglasses on.

I have seen the spots on everything from Hyundais to Bimmers. It's not just the "cheap" cars that have them.

I asked the dealer when I first got my car, and he told me to go look around - I'll see tons of cars with the glass like that - and he was right.

~HH

On a completely unrealated note, my entire rear window is impossible to see out clearly because the damn tint makes everything blurry. I need to take it back to the tint shop but I'm fearing they are going to rip half the defroster grid off the glass to fix it.