Polka-dotted windows

Lately, when the sun hits the window on a car just right, I see dots. Obviously this is some sort of window tinting, but why the dots?

Most often seen on late model, expensive cars. Any ideas?

Did somebody use one of those rain repellant or antifog products on the window? I had to use Windex to remove the repellant from my windshield. I saw spots when the sun hit the window at an angle.

Nope…

They’re very uniform dots. Almost in a checkerboard pattern…only with dots.

The explanation I’ve heard is that when the windshield is made, it’s heated to bond in the plastic layer that stops big pieces from flying around in an accident, and then quickly cooled by air jets arranged in that square pattern. You see the pattern when light is (refracted? reflected?) differently according to the uneven stresses in the glass. IIRC, you’ll only see it in polarized light (like that reflected from shiny surfaces), or when you’re wearing polarized sunglasses.

Side windows, at least, are purposely strongly treated that way so the stresses will make the glass shatter into popcorn; windshields are made with less stress because a layer of popcorn glass is really bad for visibility.

Bob the Random Expert
“If we don’t have the answer, we’ll make one up.”

A lot of car window tint kits use a sheet of plastic with a pattern of microscopic dots glued to the inside of the glass.
Reflected light viewed thru two panes of this type of tinted glass will show a visable dot pattern.
t lion

Tequila shooters and driving don’t mix.

::Pulling the spare sheets and pillow from the hall closet::

The LION,

I am a former window and door sales rep and laminated glass (same as windshields) is not produced with glues.

Laminated glass is actually two pieces of glass with a polyvinyl coating or sheet (plastic) in between that is bonded by heat and pressure.

As to why the checkered or grid pattern happens I am not sure. Automotive manufactures have started putting some coating on the glass in recent years. In my window days, I don’t recall ever seeing windows with the grid pattern. Of course, it could be due to the reflective nature as stated previously.

techchick68
As an ex autoglass installer I am aware of the difference between tempered and laminated glass.
What I was refering to was aftermarket window tint kits that use a plastic film with a microscopic dot pattern glued to the inside of the glass.
These kits can be bought at most auto parts stores and are the type that most window tint shops use.
t lion

Sorry LION,

Spose I should read more carefully next time :slight_smile:

techchick68
No problem,I am bad about skim reading myself.
I use similar type films at work in the printing trade.
The ones we use are available in various dot sizes.
Holding two screens lined up into the light generates some very interesting patterns.

t lion