Polarized lens sunglasses and car window 'spots'

What are those ‘spots’ that I see on car windows when I’m wearing my polarized-lens sunglasses?

Automotive safety glass is stretched in such a way as to make it break into little bits. Those spots are a result of that. Usually, the molecules in glass are randomly oriented, so no polarization effect occurs. The stretching changes that.

We had this same question a few months ago, with more answers. I’ll search up the link once board is moving at reasonable speed again.

BigDaddyD – Thanks for the response. It doesn’t quite explain the checkerboard effect that I see, but it’s a start.

Chronos – I searched the SDMB and the column archive and didn’t come up with anything. A link would be appreciated. Did that thread or column also explain why Pontiac minivan windshields look metallic purple through polarized lens?

If Chronos doesn’t beat me there:

You’ve got this thread:

Which, in turn, links to this thread:

(and I threw this one in for good measure: )