How to Identify Tempered Glass in 5 Ways: 2024 Guide

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We understand the sinking feeling business owners face following a report of a shattered glass window or display case. To prevent this, you want to make sure any glass installation or replacement passes safety standards and holds up under stress. One way to ensure secure and impact-resistant glazing is by choosing tempered glass. But how can you tell if the glass is tempered, especially if it was installed before you moved into the building? Keep reading to learn how to identify tempered glass via 5 simple tests.

How to Identify Tempered Glass (5 Ways/Tests)

Here’s an overview of 5 different means of identifying tempered glass:

  1. Visual inspection
  2. Light polarisation test
  3. Tap test
  4. Heat resistance test
  5. Scratch test

We’ll discuss these in more detail later, but first, let’s define what tempered glass is and its use.

What Is Tempered Glass and Why Use It?

Tempered glass is reinforced glass that has been heat treated to increase its strength and durability. For businesses, it’s an ideal choice for doors, windows, display cases, and any other application where safety and security are a concern.

Tempered glass is 4 to 5 times stronger than regular annealed glass of the same thickness. When it breaks, it shatters into small granular chunks instead of sharp shards. This greatly reduces the risk of injury. It’s also more resistant to thermal stress and impact.

Technician Measuring Glass Window

We recommend opting for tempered glass if you have large expanses of glazing, especially in high-traffic areas. It complies with building codes for applications like doorways, skylights, and windows near walkways. It can also withstand more extreme temperature changes without cracking. For best practices, ensure you hire commercial glass replacement experts for your tempered glass installations.

Visual Differences: Comparing Tempered vs. Regular Glass

When choosing glass for your business, it’s important to know the visual difference between tempered glass and regular glass.

Here are 5 cues to help you identify tempered glass visually:

  • Tempered glass has a slightly greenish tint due to the heat treatment process. Regular glass will appear colourless. The greenish hue is more noticeable when viewing the glass at an angle.
  • Tempered glass often has small surface imperfections like tiny bubbles or pockmarks. These imperfections get sealed in during the rapid cooling process. Regular glass tends to have a smoother, flawless surface.
  • Tempered glass is also slightly thicker, often 1/4 inch or more. Regular glass panes are typically 1/8 inch or less for most applications.
  • When tempered glass breaks, it shatters into small, granular pieces. Regular glass breaks into large, sharp shards that can cause injury. For safety, always wear gloves when handling any broken glass.
  • If the glass has an etched label in the corner that says “tempered” or “safety glass”, it has definitely been heat-treated. However, the lack of a label does not necessarily mean the glass is not tempered. When in doubt, it’s best to assume the glass is not tempered for safety.

These visual cues and identifiers can guide you towards selecting the right glass for your office needs and prevent any unsafe situations. For high-traffic, public-facing areas of your business, tempered glass is typically the best choice due to its enhanced safety and durability. If you’re unsure of the type of glass in your office building or don’t know how to tell the difference between tempered glass and regular glass, reach out to glazing inspection specialists for expert guidance.

5 Testing Methods to Identify Tempered Glass

Some methods for identifying tempered glass are DIY-friendly, while others require special equipment.

Here’s how to identify tempered glass in 5 ways:

  • Visual inspection
  • Light polarisation test
  • Tap test
  • Heat resistance test
  • Scratch test

1. Visual Inspection

Look closely at the glass edge: tempered glass will have a smooth, slightly rounded edge without sharp corners. Untempered glass has a sharp, unfinished edge. You may also notice small nicks or divots in the glass edge. Tempered glass has undergone intense heating and rapid cooling, so its surface is more durable.

Office worker looking through glass window

2. Light Polarization Test

Hold polarised lenses or sunglasses up to the glass. Rotate the lens and look for spots that darken — this indicates the glass is tempered. Polarised light reacts differently when passing through tempered glass due to a strain pattern induced by heat strengthening during manufacture.

3. Tap Test

Gently tap the glass with a coin or similar object. Tempered glass will produce a ringing, musical tone. Untempered glass gives a dull ’thud’. The tempering process causes the glass to vibrate at a higher frequency.

4. Heat Resistance Test

Carefully apply a small amount of heat, such as from a lighter flame, to an inconspicuous area of the glass for a few seconds. Remove the heat and check if the glass surface cracked — if not, it’s likely tempered. Tempered glass can withstand much higher temperatures due to the strengthening it receives during manufacturing.

5. Scratch Test

Scratch the glass with a hard object like a key. If the scratch feels smooth, the glass is tempered. An untempered glass scratch will feel sharp and gritty. The tempering process also makes the glass surface much harder to scratch or damage.

The visual inspection and tap test are simple DIY tests, while the other methods require caution and the proper equipment. If there’s any doubt about the glass type, it’s best to contact glazing refurbishment or replacement experts for inspection and to ensure safety. Protecting your employees, customers/clients, and goods should be your top priority.

Can Tempered Glass Be Replaced or Cut?

While tempered glass is extremely durable, it can be difficult to cut or replace. Once tempered, the glass cannot be cut, drilled, or engraved without shattering.

However, there are a few options for modifying or replacing tempered glass panels, including:

  • Cutting new pieces to size
  • Drilling holes
  • Edge work
  • Repairing chips or cracks

1. Cutting New Pieces to Size

If you need to resize a tempered glass panel, the only option is to have new pieces of glass cut to size and the tempered glass panel replaced. Measure the area carefully and have new, tempered glass cut to size. The new glass will then need to go through the tempering process to strengthen it.

2. Drilling Holes

Drilling holes in tempered glass will cause it to shatter immediately. If you need to mount hardware or fixtures to tempered glass, you’ll need to drill holes in a non-tempered glass panel and have it tempered afterwards. The tempering process will “heal” the holes and strengthen the glass. Alternatively, you can have threaded inserts or anchor points installed in the glass before it’s tempered.

Holes drilled through glass panel

3. Edge Work

Any edge work, grinding, or polishing must be done before the glass is tempered. Once strengthened, the glass edges cannot be modified. If you need round, bevelled, or polished edges, specify this when having the non-tempered glass cut to size. The glass can then be tempered as needed after edge work is complete.

4. Repairing Chips or Cracks

Tempered glass cannot be repaired if damaged or broken. Any chips, cracks, or breaks in the glass will compromise its strength, necessitating replacement. Have new, non-tempered glass cut to size and replace the damaged tempered glass panel instead. The new panel can then be tempered to match.

If you’re wondering if you can cut tempered glass, the short answer is no; they cannot be modified or repaired once strengthened. All cutting, drilling, edge work, and repairs must be done before the glass is tempered. If modification or replacement is needed, new non-tempered glass panels must be custom cut and then strengthened to match. However, you’ll typically need glazing experts to handle this — contact us today to discuss your project details.

Frequently Asked Questions

How to identify tempered glass?

Here are 5 ways to determine if a glass is tempered:

  • Check for a tempered glass stamp in one of the corners: Most manufacturers mark tempered glass to identify it.
  • Test the glass surface with polarised lenses: Tempered glass will show a distinctive strain pattern in polarised light. Regular glass will not.
  • Tap the glass with a metal object like a pen: Tempered glass has a distinct ringing tone when tapped, like the sound of a tuning fork. Non-tempered glass will have a duller sound.
  • Test the break pattern: When tempered glass breaks, it shatters into small, granular pieces. Non-tempered glass breaks into large, irregular shards that can cause injury. Check out our guide on glass spontaneous breakage for more info.
  • Use a glass thickness gauge: Tempered glass is often slightly thicker than non-tempered glass due to the tempering process.

Can you cut tempered glass?

No, you cannot cut tempered glass. Tempered glass is a type of safety glass that has been heat treated to make it stronger and more resistant to breakage. However, this process also makes it impossible to cut without shattering the glass.

If you need to cut tempered glass, we recommend hiring glazing specialists with the necessary equipment and expertise.

Why choose tempered glass?

There are several benefits to choosing tempered glass, including:

  • Safety: Tempered glass is less likely to cause injury if broken since it shatters into small granular pieces with dull edges.
  • Durability: Tempered glass is up to 5 times stronger than regular glass and resists impact and pressure better.
  • Heat Resistance: Tempered glass can withstand rapid temperature changes without breaking. It has a higher softening point than regular glass.
  • Compliance: Tempered glass meets building codes and safety standards for many applications like doors, windows, partitions, railings, skylights, furniture, etc.


This guide has explored how to identify tempered glass and ensure the glazing in your office building is safe and up to code. Next time you walk through your building, keep an eye out for those telltale signs like the smooth edge, conchoidal fractures, and light distortion. If anything looks off or the glass seems unusually thin or brittle, it’s probably best to contact glazing professionals for assessment.

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