What is the Black Dotted Pattern Around Car Windows?

It’s in front of us all when we drive, but it’s something we rarely acknowledge. Have you ever wondered what purpose the black dotted pattern around your windshield serves? It turns out this fading transition of black dots is of great importance solving multiple inherent issues with the mounting of a glass pane to a vehicle.

The black feature is called Frit; a paste of ceramic composition baked into glass, and is impossible to remove without damaging the glass itself.

It’s easy for the border lining a cars windscreen to go unnoticed.

A car’s windshield has a host of requirements to safely do its job. It has to be incredibly strong and scratch resistant, yet when damage is received it must not fracture into thousands of pieces. It must provide good visibility, and it can also contain a barely visible heating element for heated windscreens. It also needs to be properly sealed onto the vehicle to prevent an ingress of water. To protect from water penetration under the windshield, vintage cars used a gasket under the glass and usually a surrounding chrome trim would clamp the glass and gasket down. Modern cars however use an adhesive which acts as a seal from water, and also to glue the glass itself to the car.

This is where Frit lends a hand. The adhesive naturally doesn’t bond very efficiently to bare glass so Frit is baked into the pane around the edges, and provides a rougher surface for the glue to bond to. It also hides the unattractive look of the seal. Over time however, the seal degrades from exposure to ultraviolet rays from the sun, affecting its adhesion and water resistance. Fortunately, Frit provides protection against the damaging ultraviolet rays, increasing the lifespan significantly.


That doesn’t explain the black dots however. During the process that creates curvature in the cars windshield, the glass is heated to very high temperatures. The dark, heat absorbing Frit will heat up faster than the clear pane, and visually affect the finished product, so a dotted gradient is used to more evenly distribute heat. Lastly, the dot’s gradually fading pattern helps to blend the otherwise visually jarring point where the Frit line transitions to clear glass.

Frit can also have more convenient uses too, like being baked into the area around the rear view mirror to provide some extra sun protection where the sun visors can’t. It is also used in general for aesthetically mounting items on the glass, or around printed text on the glass, as the dots create a natural blending of transparent to opaque.

The Frit can be seen here surrounding where the rear view mirror and sensor box fits to the windscreen.

The fact that this design implement is barely thought about even though it is right in front of our eyes goes to show Frit is doing its job perfectly, creating a soft, gradual transition as clear glass fades to the black border. So who knew that something so overlooked can have such importance in modern car design?


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