Identifying safety glass

700rpm

700rpm

Well-known member
I heard you can tell whether your glass is safety glass or not by holding a light up to it; if you see a double reflection that means it is safety glass. Is this true? Can I count on my glass being truly safety glass if I get a double reflection?
 
The "mirror trick" and your "light trick" only work for windshield type "Laminated" safety glass.
The side and rear windows should be "Tempered" safety glass which results fom a heating process and they shatter into tiny pieces instead of how the windshield just cracks.
 
Thanks Bruce. I understand that. But what I'm asking is, is I get the double reflection, do I have safety glass?
 
I have the same question as there is no identification on my front windshield. What is the "mirror trick" and how does it work?
 
I have always held a pencil up to the window, put the eraser end on the glass, If there is a double reflection it is AS1 windshield glass. For all flat glass applications that is used for windshield and side/rear windows.
 
Yes, the double reflection means it is safety plate laminated glass. You can hold something small up to the glass and look at an angle for a double reflection. For the side windows, look at the edge when the glass is rolled down, and observe is there is a line, which is the plastic center of the sandwich. As for tempered glass, Ford did not use tempered glass in the model A. It was either safety plate, or plate glass. All Model As had safety plate windshields from the factory, but I have restored several cars that came with plate glass windshields, installed some time between new and when I got the car.
 
OK, I am getting a double reflection on my side glass, but don't see a seam where the laminate might be. How do I interpret that?
 
I looked at a mint frame and windshield glass a few years ago. When I went back to buy it an hour later some jerk had scatched an X into the windshield to check it for being safety glass.


Seems like with 2 layers of glass bonded to a layer of plastic you'd have more than just a double reflection when holding an object and looking through the glass at it at an angle.
 
I have tried the reflection method and have found it to be unreliable.
First of all, keep in mind that the safety glass designation includes two types of glass: laminated glass (2 layers of glass with a thin plastic membrane bonded between the layers) and tempered glass (one layer of glass).
The detection methods that I reccommend are the following: To verify if the glass is laminated safety glass -- gently tap the surface of the glass with a metal object (such as a quarter or better yet - a steel ball bearing) and then compare the sound to that of the same tapping on a piece of plate glass - which means in this case some glass that is known not to have the laminated layers (for example use an original door plate glass from a model A, or even the door window glass of a modern car). The sound will be much more dull if the glass is laminated and you will notice the plate glass tapping sound is much a more crisp sound. I suggest you try this on your modern car windshield and then on the side window glass and you will hear the difference, and therefore get your ear calibrated.
If you want to verify that a piece of glass is tempered (which is the type of safety glass in modern car doors and rear windows and home shower doors) - first look over the glass carefully for the manufacturer's logo indicating that it is tempereded or its safety type. If the glass is without any logo - I find the best method to verify it is tempered is by having the glass out in strong sunlight and by looking at the glass with polarized sun glasses. If the glass is tempered you can generally see some slightly darkened (like tinted glass) patterns in the glass, sometimes appearing as stripes or leopard spots. (The tempering process involves a pass through a high temperature oven that often causes the glass to have this slight polarizing affect.)
 
A few years ago either someone told me or I read that holding a business card at an angle would show a reflection. If it was double, it meant laminated safety glass. I did this on our Slantwindow Townsedan and all glass showed the double image. Looking at the edge appeared to have a center line. Recently, a friend and I discussed this. The more I looked at one glass the less I believed the "theory". I tried the card trick on a known piece of plate glass and it showed the double image. Having driven this A for a few years and also with grandchildren sent a chill down my spine! The windshield showed the same double image but I was gun-shy regardless of what came out of the factory. A shop foreman at a local glass shop said he could tell by the sound of knocking on it. I took it to him and he said he was 99% sure it was safety glass. I disregarded his advice and started taking the top off the frame and low and behold it was plate glass too! I am now in the midst of installing all eight pieces of new safety glass along with sandblasting/painting window channels, cleaning/greasing window regulators, repainting the windshield frame, new felt channels/rubber, etc. This has turned out to be one miserable task especially on a slantwindow that was restored??
I wouldn't drive it once I knew the truth............
 
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