"If only EssExTee could be so grossly incandescent" (essextee)
06/28/2019 at 11:51 • Filed to: None
0
3|
"If only EssExTee could be so grossly incandescent" (essextee)
06/28/2019 at 11:51 • Filed to: None | 0
| 3 |
When viewing auto glass through a polarized lense or filter, one can often see a slight check pattern on the glass. What causes this?
This is most apparent with sunglasses or watching professionally shot car films. The contrast of the pattern shifts as the polarization angle rotates. I see it on th e rear window and windshield but never on the side windows. Could it be the lamination layer?
vicali
> If only EssExTee could be so grossly incandescent
06/28/2019 at 12:08 |
|
Back car windows (and most side windows) are tempered for safety as you noted. The windshield is laminated.
This process is usually done by blowing cool air on the hot glass (after forming for example), this create surface stress in the glass, this energy is released when the glass break, fragmenting it.
What you see here are the marks due to the shape of the cool air nozzles. You will notice different pattern on different models due to the securities of the equipment used. The air nozzles make the cooling slightly inhomogeneous,thus the stress is can have a stronger direction making the glass slightly birefringent. Birefringence is well seen using polarized light and detector Photoelasticity
The light coming from the sky is partially polarized, light from
reflection on dielectrics (like glass) also (depending on the angle)
which explains your observations
|
If only EssExTee could be so grossly incandescent
> vicali
06/28/2019 at 12:10 |
|
Aremmes
> If only EssExTee could be so grossly incandescent
06/28/2019 at 12:13 |
|
I’ve seen this pattern on clean glass under sunlight without wearing polarized glasses, although obviously said glasses make it more obvious.
The effect is caused by the tempering process. Each of the spots corresponds to a nozzle that blows cool air on the hot glass after forming. The localized cooling produces surface stress, which control the way in which the glass breaks, and also results in
stress-induced birefringence
.