Pretty much every car on the road has a black frame, baked into the glass of the windscreen. It is around 3-4 centimetres wide and usually has a dotted pattern right next to it. While it may seem like just a strange design feature, this frame, called the frit, actually serves a purpose.
Even if you crack your original windscreen and get it replaces, they are going to install glass with a frit – it is simply unavoidable. Actually, its function has a lot to do with how windscreens are installed. Back in a day when windscreens were held in place with a rubber frame, frits didn’t exist. But now they are glued in and that is why there is a black frame baked into your windscreen.
And we do mean it when we sake “baked in”, because the frit is nothing else but ceramic enamel, which is applied during the manufacturing process, before the laminated glass is heat treated. Glass is very hard and smooth material, which is great, but because of that it glue doesn’t stick to it very well. That is one of the reasons why ceramic is baked into the perimeter of the windshield – glue sticks better to ceramic than it does to glass.
Furthermore, black ceramic enamel hides the glue from the plain sight. Glue is ugly and so it makes sense to cover it with something. Glue also needs protection against the UV rays, because they can make glue hard and brittle, which is not great, having in mind all the vibrations it has to withstand. Eventually hardened glue would simply let go in some points, probably causing the windshield to crack. That wide frit band helps keeping the glue flexible and strong.
And finally, what are those dots for? The answer is simple – for the looks. They break the hard contour of the enamel frame, allowing it to transition smoother into the clear glass. That dotted pattern does not serve any practical function. However, some manufacturers use it to hide some Easter eggs in their cars. For example, you can find a little Willys MB on the windshield of the JEEP Renegade. This little detail is formed from the same black ceramic enamel and is also baked into the laminated glass.
By the way, you can also find the frit line around the side windows of the bus as well and there it serves the exact same purpose of hiding the glue.
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