Eli5: what are the black dots around the edge of a car window? What are they called and what do they do?
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I would call them “frits” but the car industry might have a special name for them.
In essence they improve the bond between the window seal and the glass, they create a rough surface for the adhesive to bond too, and I think they help with heat distribution as well (don’t want the hot sun melting your window seal)
They are from manufacturing of the window, for even heat distribution there to prevent the window from warping when it is “baked” also they are in the closer to further apart patter mainly to be more aesthetically pleasing after the process, as after that they are very hard or impossible to remove. Also all of that black, dots included hides glue that bonds adhesive to glass to frame.
The term for these dots are “frits”
The black dots are called “frits”, and they are made of an enamel which is baked onto the glass. This enamel is a contact point between the glass and the frame of the car, something which glue can stick to and keep the glass in place.
By changing in size they gradually form a transition between the transparent glass and the opaque enamel which is viewed to appear nicer than an abrupt transition.
Most of the replies here are partially right… the black band on a car window is called a frit band. It is there to protect the urethane/glue from UV radiation. The dots are there mostly for aesthetic purposes to give a nicer looking transition from the band to the clear glass. The solid bits around the mirror are to protect the glue that holds the mirror on (also sensor/camera brackets on newer cars).
Now, to dispel some myths:
1: It is not an antenna. Although there are sometimes antennas built into windows, they are usually in the back or back quarter windows and they look like defroster lines. Bonus: if you see something that looks like a defroster at the bottom of the windshield, it is… it’s a heater for you wipers that comes on with the defroster.
2: It’s not to help with adhesion. In fact, many German cars have the frit band in the laminate layer between the layers of glass. We use a urethane primer to ensure good adhesion between the urethane and the glass.
3: It has nothing to do with heat distribution. As mentioned above, it functions as a UV blocker.
Bonus fact: Your windshield is made of two layers of glass with a layer of plastic laminate between them. This means that even if there’s a crack in the glass, your windshield isn’t going to fall in on you.
Source: am a glass technician and work with automotive glass 40+ hours a week.
Disclaimer: most of these facts are generalized with exceptions but are true for most cars.
The dots are a form of tint, to give a soft visual edge to the windshield. Makes it less noticeable to you that you’re looking through a window. Older cars achieved this by using an actual gradient, faded tint in the top edge of the glass. The dots are a cheaper way to do this because they already apply black coating around the edge to hide the unsightly glass adhesive, it’s cheaper to just use this same coating to make a faded soft visual edge. Older cars had metal or plastic trim that hid the adhesive from view.
The black dots that cluster around the crack between the rear view mirror and the sun visor are there to keep the full blown sun out of your eyes when it is at that angle. I have never worked on windows and don’t know shit about glass, but that is the purpose.
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