Many cars and trucks have solid windows and windshields with a black edge and black dots near the black edge that get smaller in size as they move away from the edge. Did you ever wonder why the black edge and the black dots are there? The explanation is pretty simple and logical.
Windshields and solid windows are held in place with a type of glue known as a urethane sealant. Glass is notoriously difficult to glue because its surface is so smooth. The black edge is called the “frit band” and is basically a ceramic based paint. This ceramic paint is baked into the glass during the manufacturing process which then gives the glue a rough surface to bond to that has been bonded into the glass during the baking process. The frit band also acts as an ultraviolet screen from the Sun’s radiation that would break down the glue over time. It certainly wouldn’t do to have your car’s windshield pop out after hitting a large pothole due to deteriorated glue.
And those dots inside of the frit band? Well those are placed there to help during the manufacturing process. Since the black edges will absorb heat faster than the rest of the glass while being heated and molded into shape, the higher heat on the edges can cause distortion in the glass that the consumer would find quite objectionable. With the black dots being placed alongside the black band, they will help absorb heat at a bit higher rate than the glass in order to eliminate the distortion caused by uneven heating. That’s why the dots get smaller as they move inward from the solid black frit band, to cause a more even heating from edge to center.
So now you know! I just found out the day I wrote this blog post and had often wondered myself what the black dots were all about.