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What is this checkered pattern on the rear window of the car? I see it on many (but not all) cars, in wet conditions. Sometimes it has a light rainbow pattern to it (similar to oil spilled on water, so mostly violet shades). I don't think I ever saw it in dry and sunny weather. Sometimes the pattern is diagonal and with slightly larger "tiles", probably depending on the car or its window.

enter image description here

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  • I'm pretty sure it has to do with polarization, but not sure. Sep 6 at 14:45
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That is an artifact of the manufacturing process. The coating is sprayed on by the glass manufacturer and what you see a slight difference in the thickness of the application due to the way the spray lines overlap.

If you look nearly all vehicles with tinted windows will show this and it's often more visible with polarized sunglasses on (in my experience) than without.

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  • Do you have any reference for what you've stated here? To my knowledge, the tinting is within the glass when it's made, not something which is sprayed on. If it were just sprayed on, you'd be seeing a lot more scratching and wear marks after years of abuse. Sep 6 at 22:47
  • Due to the way it's applied during manufacturing, it's not a coating on the surface of the glass but rather a dye that permeates into the material. That's why it cannot be scratched or removed. Aftermarket tinting is a different process with an adhesive film applied to the inside of the glass which can be scratched fairly easily.
    – jwh20
    Sep 7 at 9:42
  • Again, reference? This sounds like something made up, mainly because to my knowledge, glass isn't permeable. Maybe you aren't explaining it very well? Yes, aftermarket tinting goes on using a sheet of tinting to the inside of the glass. This isn't the same as how tinted glass is made from the manufacturer. Sep 7 at 9:52
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From what I could find, this is an artifact from the manufacturing process.

These start as a flat sheet and are "bent" into final shape. The subsequent cooling (annealing) by cool air nozzles leave internal stresses into the glass, which is what you can see. These also act as "guides" for fractures in case of an accident, causing the piece to fragment in a somewhat predictable way.

Here is a link to a previous answer to this question:

https://physics.stackexchange.com/questions/273439/grid-pattern-on-a-car-window-when-viewed-through-polarized-sunglasses

And a "How it's made" video:

https://www.youtube.com/watch?v=fbKulT5GCXQ

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  • This is plagiarized from the existing answer
    – Chenmunka
    Sep 7 at 10:27
  • Please provide additional details in your answer. As it's currently written, it's hard to understand your solution.
    – Community Bot
    Sep 7 at 10:28

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