That diffused black band with tiny black dots surrounding the windshields and the fixed glass in our cars is something you probably never notice. It’s there, you see it every day but you don’t give it much attention. You likely think it’s just an aesthetic detail and since it doesn’t affect the car’s operation, you move on.
However, there is a reason for everything.
It’s All About Frit
The frit (nothing to do with French fries) is the name given to that black band surrounding the fixed panes of our cars. According to the definition of the National Association of Manufacturers of frits, glazes and ceramic colors, frit is “a mixture of inorganic chemical substances obtained by rapid cooling of a melt, which is a complex combination of materials, turning those chemically prepared substances into insoluble vitreous compounds that appear in scales or granules”.
In short, it is a glass-like material produced by melting a mixture in a melting furnace and its subsequent rapid cooling in water. In its finest form it is applied as if it were a ceramic paint.
In the past, when the windshield and other glass panes were installed in the car, they were held in a frame surrounded by a gasket (to seal and prevent vibrations), which exteriorly was often finished with chrome strips. Over time, manufacturers began to use glues to keep the glass in place.
And that’s where frit becomes necessary. It protects the adhesive, which also acts as insulation, from UV rays that could deteriorate it. With the adhesive-insulating intact, not only does water not enter the car but the windshield remains in place.
And the Dots?
The dots serve both an aesthetic and a technical function. From an aesthetic standpoint, they allow a smooth visual transition from the black frame to the glass’s transparency. The technique used is halftoning and screening. It is the same method printers use to reproduce a color or image. It’s a printing technique still in use today. By the way, when they surround the rear-view mirror it is also to act as a sunshade.
At a technical level, it helps prevent optical distortion of the glass (as if it were a lens) during the manufacturing process. The curved shape of windshields and other panes is obtained by bending the pane after heating it in a furnace.
Since black absorbs more heat, the temperature difference between the dark area and the transparent area would be very abrupt—causing optical distortion—without a smooth transition. The dot pattern allows for a softer heat transition and thus prevents optical aberration.
