"Patterns" on old car windscreens
Discussion
My memory is shot, I'm sure I know why but during a yarn with a mate today we couldn't find the answer.
Back in the days of Escorts, Allegro's, Capri's etc, it was not unusual to see a pattern on the windscreen at a certain angle in sunlight. Best described as an oil pattern in the shape of a "house" radiator across the middle of the screen end to end.
I did say it might have been an effect of toughened windscreens which were popular back in the day as opposed to the more popular laminated we see nowadays.
I have done a search which explains the "dimpling" effect we often see,https://www.pistonheads.com/gassing/topic.asp?t=1308391 It explains the phenomenon to a point, but not the pattern I recall seeing on the windscreen of older cars back in the day.
Anyone know what caused it,why it stopped being a thing and how long ago it stopped being a thing?. Virtual beer to all who reply.
Back in the days of Escorts, Allegro's, Capri's etc, it was not unusual to see a pattern on the windscreen at a certain angle in sunlight. Best described as an oil pattern in the shape of a "house" radiator across the middle of the screen end to end.
I did say it might have been an effect of toughened windscreens which were popular back in the day as opposed to the more popular laminated we see nowadays.
I have done a search which explains the "dimpling" effect we often see,https://www.pistonheads.com/gassing/topic.asp?t=1308391 It explains the phenomenon to a point, but not the pattern I recall seeing on the windscreen of older cars back in the day.
Anyone know what caused it,why it stopped being a thing and how long ago it stopped being a thing?. Virtual beer to all who reply.
It is a property of 'zone toughened' windscreens to display the pattern that you describe.
It was caused by jets of cool air being directed at the hot windscreen glass once it was brought out of the toughening process. The jets of cool air created vertical lines of old penny (remember those?) sized areas of glass in the event of breakage.
The intention was that when the screen was broken by impact damage (flying stone etc), visibility was provided through the larger pieces of unbroken glass for the driver to stop safely or even finish their journey (!!!) assuming that the screen remained in place.
Without the zone toughening, the screen just went into small fragments and offered no visibility.
The Triplex trade name for the process was Zebrazone.
It was caused by jets of cool air being directed at the hot windscreen glass once it was brought out of the toughening process. The jets of cool air created vertical lines of old penny (remember those?) sized areas of glass in the event of breakage.
The intention was that when the screen was broken by impact damage (flying stone etc), visibility was provided through the larger pieces of unbroken glass for the driver to stop safely or even finish their journey (!!!) assuming that the screen remained in place.
Without the zone toughening, the screen just went into small fragments and offered no visibility.
The Triplex trade name for the process was Zebrazone.
On modern cars, well on my previous 1998 E36, in certain climate conditions, cold misty, you could see a pattern on the windshield. I guess you will still see them on today’s cars - the sucker pad pattern still remaining from the robot-automated pick, place and seal fixing. I had the car (and the same windshield) for 19 years, and would still see it one or two times each winter.
530dTPhil said:
The intention was that when the screen was broken by impact damage (flying stone etc), visibility was provided through the larger pieces of unbroken glass for the driver to stop safely or even finish their journey (!!!) assuming that the screen remained in place.
Without the zone toughening, the screen just went into small fragments and offered no visibility.
The Triplex trade name for the process was Zebrazone.
I’d forgotten that problem. Yes, if the screen crazed over for some reason (maybe a wayward peasant Without the zone toughening, the screen just went into small fragments and offered no visibility.
The Triplex trade name for the process was Zebrazone.
) you would be completely blind without the clear zone.55palfers said:
Polarised light (or polarised sunglasses) will show it up a treat.
Yep, I was surprised that modern cars seem to be worse than the older ones, I've some polarised 'driving' glasses which are useless as they can't read the digital readout on the dashboard unless you rotate your neck at an angle and looking through the rear view glass is hard due to the patterns on the glass.Only benefit I can see when driving other normal glasses is that you can see through the windscreen in other cars so it's useful to have a polarised filter on a dashcam.
untakenname said:
Yep, I was surprised that modern cars seem to be worse than the older ones, I've some polarised 'driving' glasses which are useless as they can't read the digital readout on the dashboard unless you rotate your neck at an angle and looking through the rear view glass is hard due to the patterns on the glass.
Only benefit I can see when driving other normal glasses is that you can see through the windscreen in other cars so it's useful to have a polarised filter on a dashcam.
I've a vague memory that some illuminated cabin items have polarised screens to avoid primary reflections.Only benefit I can see when driving other normal glasses is that you can see through the windscreen in other cars so it's useful to have a polarised filter on a dashcam.
The toughening process described above creates areas of different strain within the glass. These areas alter the phase of light passing through them. Light waves of differing phase from different areas will then interfere with each other; certain wavelengths (colours) will have a positive interference and be boosted, whilst at other wavelengths there will be destructive interference and those colours will be attenuated. Which colours are affected depends on the viewing angle, so different colours are seen at different angles from your eye. Similar phenomena can be observed due to light reflecting from either interface of a thin film such as oil on water or a soap bubble.
jet_noise said:
untakenname said:
Yep, I was surprised that modern cars seem to be worse than the older ones, I've some polarised 'driving' glasses which are useless as they can't read the digital readout on the dashboard unless you rotate your neck at an angle and looking through the rear view glass is hard due to the patterns on the glass.
Only benefit I can see when driving other normal glasses is that you can see through the windscreen in other cars so it's useful to have a polarised filter on a dashcam.
I've a vague memory that some illuminated cabin items have polarised screens to avoid primary reflections.Only benefit I can see when driving other normal glasses is that you can see through the windscreen in other cars so it's useful to have a polarised filter on a dashcam.
aeropilot said:
jet_noise said:
I've a vague memory that some illuminated cabin items have polarised screens to avoid primary reflections.
Many of these modern manufacturer Navigation-digi flat screens etc., are unviewable through Polarised sunglasses Unless your polarised sunglasses are correctly aligned with displays that work this way it will be like getting two pairs of polarised sunglasses and twisting them round till things go dark.
IIRC OLED displays in theory shouldn't be affected in the same way, but they often have a polarised filter included to reduce the effects of internal reflections.
a8hex said:
aeropilot said:
jet_noise said:
I've a vague memory that some illuminated cabin items have polarised screens to avoid primary reflections.
Many of these modern manufacturer Navigation-digi flat screens etc., are unviewable through Polarised sunglasses Unless your polarised sunglasses are correctly aligned with displays that work this way it will be like getting two pairs of polarised sunglasses and twisting them round till things go dark.
IIRC OLED displays in theory shouldn't be affected in the same way, but they often have a polarised filter included to reduce the effects of internal reflections.
Back in the late 2000's when I had my Saab 9-5 Aero I couldn't wear polarised sunglasses for driving as couldn't see the old tech LCD screen....just looked black!
Didn't have the same problem with the Nav screen of the BMW 135i that replaced it in 2011.
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