As you are peering through your windshield (windscreen) patiently waiting for the traffic light to change, you have probably wondered, “What are those little black dots doing around the edge of my windshield?” The answer may surprise you, as it did me.
What are they called? Turns out those little darlings, are called “frits”. Don’t ask me where that name came from, I couldn’t find the answer to that question but I did find out quite a bit about what functions these frits perform.
How did they get on the glass? The black border and dots are made from ceramic paint, are baked onto the window, and are virtually indestructible.
What purpose do they serve? Back in the day, auto manufacturers used to use rubber gaskets to keep windows sealed from the elements, and over top of that gasket, they’d fasten chrome trim to make it look nice and help secure the windshield. In the ‘50s and ‘60s, as auto manufacturers began transitioning from metal trim to adhesives to hold the glass in place, a way of protecting the glue and ensuring good adhesion became necessary. The frit provides an etched surface that allows the urethane adhesive to bond to the glass. The adhesive worked OK but the black goop wasn’t pretty to look at. The frit concealed the ugly adhesive and presented a more finished appearance as it transitioned from the solid black band to the glass. The outward facing side of the frit also acts as a shield against the sun’s UV rays, protecting the adhesive from weakening.
Why is there an outer solid band followed by dots of diminishing size? They make an aesthetically pleasing transition from the thick black line to the transparency of the window. The dots aren’t randomly placed; they are 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 opaque black paint juxtaposed with transparent glass.
There is a functional reason as well. Rapid temperature changes and extreme temperatures can be detrimental to your auto glass, and that goes for the cold and the heat. I learned this the hard way one cold winter morning when I turned my Discovery’s defroster on full blast to melt the ice off the windshield and promptly cracked the glass!
When the windshield is manufactured, it is baked to allow the glass to be curved The black paint of the frit band heats faster than the rest of the glass, but the dots distribute the heat a little more evenly, preventing the windshield from warping or causing an optical distortion.
Why are there a bunch of them behind my rear view mirror? Some manufacturers use this to the occupants’ advantage by expanding the dot pattern downward between sun visors to create a kind of “third visor”, which helps to reduce glare from sunlight that the driver and passenger visors can’t block. Some car makers even take it a step further and use small logos or other unique designs in place of the traditional circular dots.
So that’s the story of these simple little black dots and the many functions they perform for us.