How To Tell If Glass Is Tempered

July 4, 2022

If you are interested in buying tempered or toughened glass, then you might be unsure on how to tell if the glass you are buying is tempered. It is a difficult task. Toughened glass and regular glass are identical in appearance, but there are many practical differences. For example, toughened glass is up to 5 times stronger than regular glass and it shatters into small shards if damaged (significantly safer). As a result, toughened in commercial and residential settings, where the strength of the glass is required for safety and aesthetic purposes e.g. balconies, rooflights or balustrades. 

Toughened glass is more expensive than regular glass, due to the intense process it has to go through. So, you may want to check you are getting your money’s worth and that you haven’t been ripped off with regular glass. Below we will discuss the different methods of how to tell if the glass is tempered. 

Toughened Glass

1. Tempered Glass Is Stamped With An Identifier

Tempered glass is stamped with an identifier, which can be found in the corner of the sheet of glass. The identifier will show the manufacturer name and the CPSC (Consumer Product Safety Commission) standards, e.g. “CPSC 16 CFR 1201 CAT II”. This proves if the glass is tempered or not. If you have purchased the glass directly from the manufacturer, then the marking will be obvious. 

The tempering process to create toughened glass is intense and more costly than regular, this is why it is important to be able to tell if you are working with toughened glass. The process consists of heating regular glass up to temperatures between 620°C and 650°C and then cooled down with blasts of ice-cold air. This compresses the glass and makes it very tough and resistant to heat damage.

This method of checking is not always reliable, as a frame may cover the marking or fading may occur over time. We suggest that you pair this method up with another one that we have suggested if you can’t find the mark.

2. Slight Imperfections

A common mistake that is made when identifying toughened glass is believing that imperfections suggest that the glass is not tempered. If there are slight imperfections on this glass, this can be a sign that the glass is tempered. One of the common imperfections include slight bending, due to the tools used in the tempering process. Also, the surface of the glass might have small scratches, which are caused by small pieces of debris that melt on the surface during the heating process. 

3. Smooth Edges

One of the ways you can check if the glass is tempered is by inspecting the edges. Feel the edges of the glass and determine what type of glass it is. Tempered glass has a very smooth finish, due to the heating and cooling process that it goes through to make it toughened. This gives the edges a smooth and sleek look and feel. Whereas, with regular glass, the edges will typically be rough.

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4. Use Polarised Glasses To Identify Tempered Glass

Another way you can tell if the glass is tempered is by putting on polarised sunglasses and looking at the glass in the sunlight. Polarised glasses block out certain types of light, which is why they are useful to use in this case. You can tell if the glass is tempered if you notice lines stretching along the pane, which is created during the tempering process by machine rollers. Often, these are difficult to spot, so look carefully and take them in. 

5. Tempered Glass Can’t Be Drilled (It Will Break)

There are much easier ways to check if the glass is tempered than drilling it, but it is worth noting that toughened glass can’t be drilled into as it will break. 

Tempered glass breaks into small glass shards, rather than large glass chunks like regular glass, as the glass breaks parallel rather than perpendicular, This makes toughened glass significantly safer, as the small, round shards reduce the harm and damage caused by glass breaking. If you are looking for even safer glass, then you should check out laminated glass. Laminated glass has an extra layer between the two sheets of glass, which prevents the glass from breaking at all! 

toughened glass

6. Score a Line

Scoring a line in the glass is another way to be able to tell if the glass is tempered. However, we only advise using this technique if you are removing the glass. It should never be used on brand-new glass.

To be on the safe side, you should hire a glass professional to cut the glass. However, you can do this yourself by purchasing a window-cutting tool online or in a DIY store. You should not use a standard DIY knife for this task, as it can be extremely dangerous as well as inefficient. 

The appearance of the line indicates whether the glass is toughened. If it is toughened glass, the line will be bumpy and uneven. But, if it is regular glass, then it will be a relatively straight and clean line. 

Benefits of Tempered Glass

There are many benefits to using tempered glass in your home or business, here are just a few: 

  • Strength: Toughened glass is up to 5 times stronger than regular glass. This makes it more durable and safer than other options available. It is extremely hard to break. 
  • Safety: Tempered glass is extremely safe. It is very unlikely to break, but if it does, it shatters into safe, small pieces which limit the damage and injuries it can cause. 
  • UV Protection: Another benefit is that toughened glass absorbs 65% of sun rays, which is safer and protects you from harmful, excessive light. 
  • Versatile: A great thing about toughened glass is its versatility. It can be used at home or in your business, and with many different applications in both settings. Check out TuffX’s gallery for inspiration on how you can use glass. 

There are many more benefits of toughened glass, read more about these in our blog post ‘10 Benefits of Toughened Glass’.