For the past several years or so automobile and truck windshields have had a pattern of black dots installed around their edges. What purpose do those dots serve?

I had to go outside and check my own vehicle for black dots. That's called field research. And by golly you're right. There is a pattern of black dots around the edge of the windshield.
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I wonder why that is. Somebody should try to find out. Oh, yeah, that's what I'm supposed to do. OK, I'll give it a shot.

And I'm glad I did because it turned out to involve frits. Frits. What a great word. I thought for a minute it also involved frims, but that turned out to be a typo for firms.

Anyway, this is what a frit is. It's a band of black enamel that gets baked into windshield glass during the manufacturing process. The black dots you see are the border of the frit.

This band of enamel usually is sort of etched on its inside surface, and they use that etching to help bond the windshield to the frame of the vehicle with adhesive.

Why is it black? Because the black enamel on the outside surface of the windshield protects the adhesive from ultraviolet light. That's good, because you wouldn't want to be driving along and all of a sudden have your windshield fall right off your car because the glue had melted.

Rather than a straight black edge, the dot border blends the solid band into the clear glass, says Steve Coyle at Auto Glass Specialists. Some windshields also use the dots as a third sun visor to block the Sun behind the rearview mirror where most visors don't reach.