How to tell if glass is tempered.

[Gold Stripe]

Looking for a scratch is not at all a good measure. Tempered glass generally doesnt explode until you actually break through it. Just cutting the surface wont cause an eruption.

In my experience the cell phone with polarized sunglasses has worked every time. You just have to know what you're looking for.

 

[laugh]

Like uncleof6 said most 55's are tempered. So much so that I would assume any 55 was tempered on all sides unless I could find out for sure it wasn't from the manufacturer.

 

[stugray]

How about this wacky idea:

For those of you that KNOW your piece of glass is tempered, measure the thickness & post it here.

For those of you that KNOW your piece of glass is NOT tempered, measure the thickness & post it here.

If we get enough people to populate the database, we can have a lookup: If you have a 55G and your thickness is X, then it is tempered/not-tempered.

How about a "RC-glass thickness calculator for tempered/or-not"

Stu

 

[pepsiDX20]

Go to wallyworld, buy some cheap polorized sunglasses. Hold up your laptop screen to glass, look through glass at screen. If it's temepered you'll see stripes or spots on the screen. If it's not it will look normal. Check the bottom first as those are almost always temepered. Another thing, try to check indoors. I tried it outside first and couldn't tell eitherway.

 

[hllywd]

Using the LCD screen method would definitely work best in a low light situation. If you have filters like I show above, I like to test it outside in bright light. Just orient the filters to block the most light like in the second pic with one of the filters on each side of the glass to be tested. move them simultaneously across the glass to see the light and dark areas in tempered glass.

This is what you're looking for:

Since you're looking at such a small area it won't be as obvious, but the light and dark areas will be there if the glass is tempered.

Hope this all helps!
Tim

 

[stugray]

"This is what you're looking for:"

Except car windshields are NOT tempered, only the side & (sometimes) the rear glass.

Stu

 

[hllywd]

Sorry Stu,
I didn't add that in there this time... pretty sure all rear windows are tempered any more... I remember some like in '60s and older pickups that were not. Windshields never are. So that pic is definately a rear window!
Tim

 

[MarCn]

very useful method.

 

[stugray]

NO, that pic is clearly the front of the car.

The effect must be from the rear window, or the method is not trustworthy ;-)


Actually after thinking about it some more.

These effects you are seeing in tempered glass is not really a direct observation of the "temperedness" directly.
Those are "fringes" that are there because the object is under stress/strain.

Tempered glass is definitely under strain, so that is why you see the fringes.

Windshields are laminated glass. Perhaps laminated glass is ALSO under stress/strain.

Stu

 

[hllywd]

Your right, I guess I always just looked at the glass in that pic. Not sure how to explain that one... I sorta plagerized the pic to illustrate the effect we're looking for. They don't use tempered in windshields because of the ejection hazard for unrestrained occupants if it breaks, and bug-on-the-window syndrome if it doesn't...

I wear polarized sunglasses and have never seen the effect on a windshield in person, always sides and rears... I really think that pic is doctored somehow now that you point it out...

 

[hllywd]

Hmmmm.... further I wonder what kind of car that is, the steering wheel is on the wrong side. Suppose it's possible tempered is allowed outside the US?

 

[Amp2020]

Tinted windows will show the same effect. I believe most window tinters use heat to deposit a layer of carbon into the surface of the glass to tint it. This usually gives a checker board pattern of dark spots. Most aquariums will not have this patter but instead will have lines or bars going across them. My 75 has one inch dark bands with a clear 1/2" gap between them. My 55 has much thinner dark bans with 1/2" gaps between them. I also have lots of tempered sheets of glass from salvation jobs(store front glass door, display windows, and display cases). The pattern depends on the manufacturers method of tempering and how much they temper the glass. I also have some sheets that are hardened(very small amount of tempering) and no one here would have been able to test it with these methods if you didn't know where to look. The center of these sheets show no dark markings at all. But along the edges is a single dark ban that can barely be seen. So I just want to warn everyone that just because you don't see any dark lines in the middle of the glass doesn't mean it's not tempered. Make sure you cheack all sides and corners.

 

[stugray]

Yeah, there was a fairly heated debate a while back about windshields vs side windows & tempered or not.

Some said that windshields were tempered while we know plenty of reasons that is a BAD idea ( rock hitting windshield & it exploding but not falling out due to plastic laminate = zero-visibility ), or the reasons hllywd mentioned above.

Anyway, one of the things I pointed out is there are varying levels of "tempering" or "toughening". I think trying to drill "toughened" glass is where we hear the urban legends about being able to drill clear through and have it explode after the fact.

I once had a temper tantrum with a table-top arcade game ( it was mine ) when I was a teenager. I got mad & stomped the top glass (tempered) then sat back down. I heard a very high pitched whine increasing in frequency ( I have super-human hearing ;-), then as the pitch reached it's maximum, the entire glass table top exploded - maybe 20 seconds after I kicked it. _ Cool but dont try that at home - I was a professional idiot back then.

Stu

 

[fredsfrags]

1

Check the corners of the piece of glass. If the glass is tempered, it is required for the manufacturer to etch the four corners, identifying it as tempered or safety glass.
2

Look for dimpling and imperfections, which were caused during the heating process. Tongs used to remove tempered glass from heat often leave small impressions in the glass that can identified if you look closely.


View glass at an angle through polarized sunglasses. Polarized sunglasses expose black lines in the glass that occurred during the heating process. These lines become more prominent at sharper angles.
4

Hold the glass out straight and look for signs of warping or bending. Sometimes the heating process causes mild warping that is easy to identify.
5

Analyze the shattered remains. Safety glass is designed to shatter completely, leaving behind no large shards on which a person might harm themselves.

 

[redfishblewfish]

I don’t care about car windows!

I’ve used the polarized sunglasses/video screen method a number of times of fish tanks, and it works just fine…..clearly showing tempered and non tempered glass.

Forget about that label on the bottom of some tanks. I had a 40b with a “Do Not Drill” label on the tank. Using the glasses/video method, I found the bottom to be tempered while the sides were not. No problem drilling the sides.

 

[hllywd]

I don't care about car windows!

That's fine, you don't have to.

The significance of side car windows is that they are known tempered glass, a place to practice your testing method. It may be important for the first time driller to know his testing method to determine whether or not his tank is tempered is valid. Or it may not...

 

[redfishblewfish]

That's fine, you don't have to.

The significance of side car windows is that they are known tempered glass, a place to practice your testing method. It may be important for the first time driller to know his testing method to determine whether or not his tank is tempered is valid. Or it may not...

I will agree, especially if it's your first time, that you see the difference between tempered and non-tempered glass, and how the video screen looks when looking through the glass with polarized sunglasses.

Good stuff!

 

[IUfan]

What am I doing wrong here? I have tried this over and over, and I don't see anything, just looks totally clear. I even tried my car side-window and saw nothing, so I must be doing something wrong.

I tried my laptop, and also my iPhone. Held it tight up against the glass and looked through the glass at the phone screen, whilst wearing polarized sunglasses and even 3D glasses. Whatever I try I don't see anything, can anyone tell me what I'm doing wrong. What am I meant to see? The pictures in that article aren't clear. If its not tempered is it meant to go black?

 

[dcfluegel]

great tips - thanks! may have saved me some major headaches here!

 

[uncleof6]

1

Check the corners of the piece of glass. If the glass is tempered, it is required for the manufacturer to etch the four corners, identifying it as tempered or safety glass.

Aquarium manufacturers don't and are not required to do so. Even if they say it is not tempered it just might be--they ran out of regular float glass and used tempered. Even if they say it is, it may not be--same reason in reverse. What works with any other endeavor, is not the case with aquarium manufacturers and dealers/suppliers: there are no rules, no regulations (especially with lighting)--and not a great deal of honesty for that matter.

2

Look for dimpling and imperfections, which were caused during the heating process. Tongs used to remove tempered glass from heat often leave small impressions in the glass that can identified if you look closely.

Don't count on it.

3
View glass at an angle through polarized sunglasses. Polarized sunglasses expose black lines in the glass that occurred during the heating process. These lines become more prominent at sharper angles.

Sometimes, sometimes a false positive, sometimes a false negative.

4

Hold the glass out straight and look for signs of warping or bending. Sometimes the heating process causes mild warping that is easy to identify.

Perhaps, but don't count on it--and don't base a judgement on it.

5

Analyze the shattered remains. Safety glass is designed to shatter completely, leaving behind no large shards on which a person might harm themselves.

Safety glass, IIRC, is laminated, such as a windshield. It does not shatter, rather many many cracks, but generally remains in "one" piece. Tempered glass shatters into a million rounded bits.


This is the 100% accurate DIY method to determine whether glass is tempered or not. But would be better to know before hand, would it not?