The Lost World of Friese-Greene

I've found that only toughened windsceeens give the vertical rib pattern; lamininated glass seems to be immune to this - that's why polarising sunglasses are OK with laminated. I'll check with a real photographic polarising filter tomorrow when it's light.

In article , Martin Underwood writes

I think it varies, depending on the method of manufacture. I've certainly seen some laminated screens that show patterns, but not the pronounced grille pattern of toughened windscreens.

I tend to use my pola filters mainly for fish watching nowadays though :)

Regards,

Simonm.

Not so. Early cars had laminated glass - it used to go yellow with age. Think that's where the name Triplex came from. I *think* toughened only became popular after WW2. And even not then were all windscreens toughened. My first car was a 1953 MG Magnette and that had a laminated screen which was original - you can date them by the logo. I removed it to replace the rubbers which were perished and leaking, and when I carefully laid it down it cracked. I replaced it with a toughened one, but this was in the '60s.

As I recall, old flat automotive glass was usually laminated, and the centre layer was prone to yellowing especially from the edges where I guess the integrity of the sandwich seal was most likely to start to fail. Toughened glass, especially the later "Zebra Zone" style, was only seen in curved glass. I imagine that the technology back then wasn't up to cost-effective curved laminated glass, and toughened - i.e. case hardened - glass was cheaper.

You could be right, but it didn't really have that look about it (the interior looked too bright), and I could have sworn the windscreen seal was missing too. I've now remembered it was the "Piranha" from the Man from U.N.C.L.E. series. The car had no engine in - they pushed it down a hill at the end of the feature to show it being "driven". So, it's possible that it was in mid restoration and the screen wasn't properly fitted anyway.

That has to be a cross-polarising effect, surely. You're eliminating the reflections effectively enough, but some of the transmitted light is also eliminated because the pre-stressing has polarised it at the wrong angle. Fiddling about with a polariser, looking out of my window at the car-park, I can't see any of these 'interesting' effects on any of the cars parked there. The biggest issue is how much darker the interiors appear than the surroundings.

It was a very low production sixties kit car with a distinctively curved screen, so I expect it would have been fitted with whatever could be made cheaply enough in small quantities.

Willy Eckerslyke wrote in e2sk4f$sia$ snipped-for-privacy@fantastix.bangor.ac.uk:

That's because modern cars tend to have laminated rather than toughened windscreens. I think my early-1980s Renault 5s had toughened, but every car since then (starting with 1988 VW Golf) has had laminated. I'm judging this by the fact that I got the horrible pre-stress pattern on the Renaults with polaroid sunglasses (I had to keep a special set of tinted glasses in the car, just for driving) but I've had no problems using them in any more recent car.

I hadn't realised that laminated glass pre-dates toughened glass, fell out of favour and has only now become almost universal again: I'd imagined that laminated was a fairly recent phenomenon and that early glass was all toughened - or else (on very early cars) ordinary window glass :-(

What surprised me was that the sunroof in my first Golf was only toughened. I got in my car one morning to find the inside covered in glass "pebbles" and a three-inch hole in the sunroof - probably where it had been hit by a bit of frozen wee from a passing aeroplane since I was under the approach path for Heathrow. With laminated glass the glass might have crazed but maybe wouldn't have actually been penetrated by the "missile". I'm glad my insurance had to pay the £300 bill for a new piece of sunroof glass.

Yebbut, some of them are parked with their backs or sides to me. I think side windows are usually toughened so that you can smash them and get out if you need to. But then, I've never noticed those off patterns on side windows, so perhaps it's done in a different way.

Willy Eckerslyke (oss108no snipped-for-privacy@bangor.ac.uk) gurgled happily, sounding much like they were saying :

Because it's cheaper, lighter, and less likely to be subject to flying stones...

Probably because they're less curved? I've seen the "zebrazone" type pattern on some older rear windows.

Some modern stuff does now have laminated side/rear glass, but that's for "security" and to make 'em quieter. Also the occasional double-glazed (think lam but with a tiny airgap) - again, quieter, but also helps to reduce misting. Not that that's relevant, because the kinda car with it tends to have aircon as a given...

Adrian wrote in Xns97B36EFC8FE46adrianachapmanfreeis@204.153.244.170:

That's a point: my car has toughened side windows but there's no pattern. Must be because the glass needs less stressing when it's almost flat so the stress marks of a (curved) toughened windscreen are not there. I know they're toughened because I've twice had to clear up all the glass "pebbles" when a towrag has broken into my car - both times without stealing anything!

I can see you feel strongly about this and sympathise! I remember once using a Hillman Hunter screen lying on the lawn as a trampoline having seen someone doing it on the telly. It bounced quite nicely three or four times and then disintegrated. I can say for sure that Rootes were using toughened glass windscreens in 1973.

You should have seen the Z cars used for studio back projection stuff. No bodywork in front of the windscreen to allow the cameras in close. No windscreen - partially for reflections and to allow a boom to be used for the sound. No mechanics whatsoever - the body was mounted on castors for easy moving. But hey - it looked ok in those days. And got an audience of millions.

You'd have a hell of a job to smash a side window without some form of tool. Even with the correct 'hammer' it took 6 goes to break a rear door window on an Audi for The Bill recently. It left a big mark each time, though.

How old are you, Dave?

I know that a Ford Transit van window can be broken with no more than a half-brick and an arm swung back a couple of feet - no need for a hammer and screwdriver. I witnessed a man do precisely this a couple of months ago... and received a commendation from the police last night for helping to catch him and restrain him till the police arrived.

The first time my own car was broken into, it was parked very close to a wall - probably there was about a foot between the side windows and a high wall. But some "kindly soul" managed to smash one of those windows despite not being able to get a good swing at it. The windows on the other side where there was plenty of space were untouched. Thank goodness for deadlocks: even after he'd broken a window, he couldn't unlock any of the doors to get inside. So he took it out on the keyholes instead! Bastard! The second time I was probably within a hundred yards or so of my car and yet I never heard the explosive bang as the energy stored in the toughened glass was disippated.

Very very old. Started work with the BBC in 1962. ;-)

In a previous existence I had to organise some very simple tests of means of escape from railway coaches. We equipped a volunteer with a variety of means of breaking the toughened glass, and urged him to panic as if the coach was on fire. The first choice weapon was a fireman's axe, with which he took a mighty swing at the centre of the window. It bounced off. We gave him one of those "toffee hammers", now sealed behind glass (how do you break into the box to get it out?) in modern railway coaches. Nothing, no matter how hard he hammered. The we showed him how to use it - rest your knuckles on the window, and give the hammer a quick flick, but as close to the corner as possible. Bingo!

An automatic centre punch is also effective and a lot more subtle than a house brick.

It was my understanding that toughened was usual in door windows because it took flexing much better than laminate. I suppose it must have improved because a good slam of the door could at one time crack laminate or maybe the glass was just old and delaminating

Malcolm.

Yet your local car stereo thief uses nothing more than a pointy stone.