You may have noticed a lot of car windshields have these random black dots along the top edges, but you probably haven’t given much thought to them. Sure, they look cool — but those black dots and the black rims that surround them are there for a reason, and happen to serve an important purpose — one that doesn’t help to defog the glass.
All of those tiny black dots have to do with how car windows are made. In the 1950s and ’60s, car manufacturers applied an adhesive to hold car windows in place, instead of metal trim. It did the job — but wasn’t visually pleasing.
Eventually, new windshield technology was created in the form of black rims you see around car windows today, called “frits.” The frits (and the dots that border them) are made from ceramic paint. The frits hide the icky-looking, but important adhesive from view. Also, since these painted rims are baked into the window, they’re all but indestructible. They hold the glue in place, which holds the windshield in place.
“As for the dots, they’re there to make an aesthetically pleasing transition from the thick black lines to the transparency of the window,” said glass technician, Tyler Rehder, with Discount Auto Glass in Joplin.
The dots aren’t randomly placed. They’re positioned in what’s known as a “halftone pattern,” getting smaller and farther apart as the black recedes. This pattern is less jarring to the eye than black paint with transparent glass. But despite the shape, the dots aren’t just eye candy.
“Besides the visual effect, they provide temperature control. Window and windshield glass must be heated and bent into shape before being installed. Black-painted glass heats faster than the rest of the window. The dots distribute the heat more evenly, which prevents the windshield from warping in the heat,” said Rehder.