Have you noticed those black dots on the car windows and that black band running along the edge of the glass? You must have done so, but do you know what is their purpose? The answer lies in the explanation of one automotive glass manufacturer, United Kingdom-based company called Pilkington that has been in the glass business since 1826. They were asked for an answer, so they gave one.

It’s All About the Frit! The Black Dots on the Car Windows are There for Purpose After All.

According to them, the black band around the edge of the glass is called “frit,” a baked-in ceramic paint that’s almost impossible to scrape off. That frit band along the edge of the glass, serves three main purposes.

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First and foremost, it acts to prevents ultraviolet sun rays from deteriorating the urethane sealant. Since the sealant doesn’t just keep rain out of the car but holds the glass in place too. That matters indeed. You wouldn’t like is the sun to cook your adhesive, and send your window flying out the next time you hit a speed bump. The frit band is a visual barrier, preventing people from seeing that nasty glue from outside and it also acts to provide a rougher surface for that adhesive to stick to.

The auto manufacturers used to use gaskets to keep windows sealed from the elements, and to prevent the windshield from rattling out, they’d fasten chrome trim over top of that gasket. To hold the glass in place, in the ‘50s and ‘60s, auto manufacturers began transitioning from metal trim to adhesives. To protect the glue and ensure good adhesion, the frit band became standard on essentially all automotive windshields.

The “Dot-Matrix” You See on Windows is a Halftone Pattern

The pattern simulates a smooth gradient by gradually decreasing the size of the solid black dots as it moves inwards. It’s all about visually pleasing transition from the black frit band to the transparent glass. Windshields are bent in a hot oven and since the frit band is black, it tends to heat up faster than the glass. The faded dots are used to help create a more even temperature distribution, minimizing this distortion.

frit-band

Photo: Cadillac

On modern cars, there’s another group of dots on the windshield right behind the rear view mirror called “third visor frit,”. These dots are there to block the sun as it beams in from between the two front sun-visors.

It is simple, and maybe not the most important thing you have read all day, but it is good to keep you informed.