How To Tell If Glass Is Tempered Or Not (Here Are the Details)

Upgraded Home Team
by Upgraded Home Team

Strengthened safety glass is a critical safety material for use in homes, commercial buildings, cars, and more. Tempered glass is about three to four times stronger than traditional “annealed” glass. The panel’s strength is increased by undergoing extreme thermal or chemical processes.

Tempered glass is often used where durability is critical, such as car windows, shower doors, and more. Also, unlike annealed glass, tempered glass will not shatter into millions of sharp pieces. When broken, tempered glass is relatively harmless and cleaned up easily.

To tell whether glass is tempered, you can look for a watermark or stamp on the panel, as this is the simplest and most effective way to tell whether the glass is tempered. If your glass is not stamped, you can examine the edges and surfaces, and look at the glass through polarized sunglasses.

Usually, the process is as simple as finding the watermark. If this is not the case, follow our steps below to help you determine if your piece of glass is tempered.

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What Is Tempered Glass?

Tempered glass is a durable alternative to annealed glass. It is created by putting glass through extreme conditions. One common way that manufacturers do this is through a thermal tempering process.

For thermal tempering, the panel is placed in a furnace where it is heated to almost 1,200 °F. The glass is then quickly cooled with air drafts in a process called “quenching”. This rapid heating and cooling creates “compression” in the panel, which gives it its strength.

Tempered glass and heat strengthened glass are not the same thing. They do undergo similar heating processes. However, heat-strengthened glass is only about 2 times as strong as annealed. If broken, it breaks into a few large pieces, while tempered breaks into many small, cubical pieces.

Chemical tempering is another method that is rarely used, due to the high costs. Various chemicals replace the heating and cooling process to accomplish the same effect. The chemicals alter the glass’ composition to create “compression”. In either case, if the glass is tempered, it should be easily identifiable in just a few steps.

How To Tell If Your Glass Is Tempered

Now that you know how tempered glass is formed, it is important to be able to identify it in your home.

Look For Labels

Tempered glass manufacturers are usually required to stamp the glass with the word “Tempered” or “Temp”. If your piece of glass is marked like this, then your search is over and you can be certain that your piece of glass is tempered.

If you have a new piece straight from the manufacturer, the stamp will be easily visible. The stamp may be obscured or rubbed away if the glass in question is already framed or otherwise not new. If this is the case, proceed with our next steps.

Score A Line

If you can’t find a label, take a sharp knife and score a small line in the glass. If it is regular annealed glass, it will create a clean, white line. If it is tempered glass, it will cut unevenly and the material will chip and flake off.

Annealed glass is relatively simple to cut using the proper tools. This is not the case with tempered glass. It will shatter and crack if an attempt to cut it is made. Only score your piece if you plan on cutting it anyway as you will leave a permanent scratch on the surface.

Polarized Sunglasses

If you still haven’t been able to determine if the glass is tempered, try putting on some polarized sunglasses. If the glass is tempered, you should see rainbow patterns or other artifacts when viewing the piece of glass. If you can see clearly through the piece of glass, it is probably not tempered.

Because of this effect, polarized lenses are not recommended for driving. The side windows of the car are usually tempered, which would create a hazard when viewed. If the glass is frosted, such as in bath or shower applications, then this method may not work properly.

Search For Blemishes

Search your panel for any imperfections, warps, or dimples. If you are able to find some, then you most likely have a piece of tempered glass.

The glass undergoes extreme heat as part of the tempering process. The machinery used to handle the hot pieces usually leave an indent in the panel, only identifiable with a thorough examination. You may also see some surface scratches left behind by the manufacturing equipment and process.

Examine Edges

Tempered glass goes through extra stages of processing, usually leaving the edges completely smooth and beveled.

The edges of annealed glass usually have scuffs and other imperfections. If your panel has a processed, finished appearance on the edges, it is most likely tempered.

Analyze The Corners For Marks

These are normally very little and can be found in one of the glass sheet’s corners. In fact, in the shape of a stamp, the bug is supposed to function as an identifier for tempered glass.

The stamp is a crucial emblem to establish whether the glass is tempered or not, as it shows the manufacturer’s name and the CPSC (Consumer Product Safety Commission) regulations.

Are you purchasing the glass from the manufacturer or through a contractor? It’s not difficult to observe the etched sign. If you come across one on your sheet, you’re probably dealing with tempered glass. If not, you’ve probably been duped and have a standard annealed glass instead.

Where Is Tempered Glass Used?

Tempered glass is used in many applications. It is often chosen for skyscraper windows, as it can withstand the wind and other elements. You can usually find tempered glass near the entrance of most homes. The extra strength panes are used in windows near heavy doors to prevent the glass from shattering. This is usually required by building codes.

It is also used on most cell phones. It does not scratch easily and won’t harm the user if broken. In addition, aquariums and glass table tops usually employ toughened glass in their construction.

Why Should You Buy Tempered Glass?

Tempered glass, as previously stated, can tolerate high temperatures. As a result, it is an excellent protective covering for your cell phones as well as other interior demands.

It doesn’t scratch or damage as easily as other materials. It’s a strong glass that protects your gadgets while also serving as a decorative element in your home. Tempered glass is nearly five times stronger than plain glass and should be used to protect. It simply gives the most effective shock absorption!

This glass is long-lasting and completely safe. If it breaks, however, it shatters into thousands of minute but harmless fragments.

Can Tempered Glass Spontaneously Break?

Tempered glass has been known to shatter in a seemingly spontaneous way. However, this is usually related to previous damage. If a piece of glass has an existing surface or edge damage and then experiences a small amount of extra force, such as heavy winds, it may break unexpectedly.

Be sure to examine your tempered glass regularly for signs of distress or cracks. If you are able to find irregularities, the strength of your panel may be compromised.

What Happens When Tempered Glass Breaks?

When regular annealed glass breaks, it shatters into sharp pieces that pose a health hazard. When tempered glass is cracked or broken, the entire piece shatters into little pebbles, free of any sharp points or edges.

This is why tempered glass is often used in places where safety is critical and glass is often broken, such as the entrances of a home, car windows, or glass tabletops.

Wrapping Up

You have now been provided with a variety of methods for determining if a piece of glass is tempered. Finding labels, examining the edges and surfaces, scoring a line, and viewing through sunglasses should all assist in categorizing your panel of glass.

If you are unable to confirm that the piece is tempered after using these steps, then your panel is most likely traditional annealed glass. Read on for common questions and more information regarding tempered glass.

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Related Questions

How strong is tempered glass?

Tempered glass is around three or four times stronger than annealed glass. It can withstand some abuse, but it will still break under pressure. Bulletproof glass, a reinforced version of tempered glass, is known to break when large projectiles are traveling faster than 35 mph.

Can I drill a hole through tempered glass?

Unfortunately, this is not possible. The tempered glass will completely shatter if one attempts to cut or drill through the glass.If you must have a hole in the panel, you will usually need to have a custom piece created for you. If your piece of glass ended up being annealed glass, read about how to bore a hole through it without using a drill!

Upgraded Home Team
Upgraded Home Team

We are a team of passionate homeowners, home improvement pros, and DIY enthusiasts who enjoy sharing home improvement, housekeeping, decorating, and more with other homeowners! Whether you're looking for a step-by-step guide on fixing an appliance or the cost of installing a fence, we've here to help.

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