They have more than just one purpose. <small> Cover image via Tundras </small>
At some point, while driving your car, you may have noticed little black dots and black band running along the edge of the windshield
And may have wondered, “What purpose do they serve?”
We will talk about those little black dots later because first, we need to talk about that black band running along the edge of the windshield.
It’s called “frit”, a semi-transparent glossy substance that serves two specific purposes.
It is literally baked into the edges of the windshield from the factory, accompanied by the border of black dots, which we will discuss after this.
The purpose of this frit is to provide an etched surface that allows adhesive to bond to the glass. When a manufacturer installs a new windshield, the glass is bonded to the vehicle with the frit as the contact point between the glass and the frame.
Now here are the frit band’s two specific purposes
From its inward facing side, the frit provides a surface that allows adhesive to bond to the glass, and from outside, it acts as a shield against ultraviolet Sun rays in order to protect the adhesive bond, which would otherwise be weakened by continual exposure.
Additionally, the frit also has an aesthetic purpose as it nicely conceals the adhesive used to install the windshield and provides a more “polished” appearance.
And now let’s talk about those little black dots
Those black dots appearing in a halftone pattern help distribute temperature evenly to lessen optical distortion in the glass, also known as 'lensing'.
You see, when windshields are made, they are bent in a hot oven. During that process, because the frit band is black, it heats up much faster than the glass.
A sharp thermal gradient between the frit and the clear glass can cause optical distortion, also known as ‘lensing’, so those ‘gradually sinking’ black dots help lessen this phenomenon by dissipating the heat and spreading it out evenly.
Additionally, the little black dots also provide a more visually pleasing transition from the black frit band to the transparent glass.
There’s another group of dots on the windshield right behind the rearview mirror of modern cars. It’s called the ‘third visor frit’.
While many people assume they are an antenna, but that's wrong.
The “third visor frit”, as those dots on the glass behind the rear-view mirror are called, was created to help block the sun as it beams in from between the two front sun-visors.
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