How to Tell if Your Window Glass Is Genuinely Tempered

How to Tell if Your Window Glass Is Genuinely Tempered

January 10, 2022
Martin Whitmore, President of US Window & Door
looking at tempered window glass

You can find tempered or toughened glass just about anywhere. For starters, there’s a good chance that you’re reading this article on a screen made of tempered glass. Even when you are in a car or bus headed downtown, you are probably surrounded by tempered windshields and windows as well.

Tempered glass is well known for its safety due to its exceptional durability and resistance to a host of things. This type of glass is commonly found in windows, doors, furniture, and appliances in both residential and commercial buildings. You’ll also find that some of the safety equipment we use, such as goggles, comes with tempered glass. 

Most people only think of how tempered glass is used as a screen protector for mobile devices. However, its applications go far beyond that. Automobile manufacturers utilize the glass’ high resilience in vehicles, where it functions as the windows, windshield, and side mirrors as well.

Moreover, doors can be made of tempered glass, from hinged and bi-fold to French and sliding doors. The relevance of tempered glass is not even limited to its strength. This type of glass also possesses excellent heat resistance, so it’s often used for ovens and microwaves. 

tempered glass

In modern architecture and technology, the application of tempered glass has attained new heights. Not only is this reinforced safety glass used in constructing buildings, but it also protects passengers in public transportation. Toughened glass fractures differently than regular glass, which is one of its key characteristics. Rather than shattering into large, irregular bits, tempered glass breaks into small, even shards. This removes the risk of sharp edges making it a far safer alternative in the event of an accident - the theory being that these little bits are nowhere near as dangerous as sharp shards. For this reason, toughened glass is commonly referred to as “safety glass.”

So what exactly makes tempered glass different from the standard glass we have in our homes? Well, it all boils down to their different methods of production. Tempered glass derives its name from the tempering technique that is used to manufacture it. This heating and cooling technique reinforce the glass. Tempering may also be accomplished chemically, although this method is far less popular due to its high cost.

Tempering is the process of heating annealed or regular glass to 1112 °F (or 600 °C) and then rapidly cooling or quenching it with a blast of high-pressure air. This procedure creates tension in the core of the glass sheet, making it much more robust than annealed glass and necessitating greater power or pressure to break it.

With such effort put into production, it is no surprise that toughened glass would be costlier than the average glass. Hence, extreme caution is to be exercised when seeking to purchase one. Taking time to do your research and reading informative articles just like this one is a fantastic step to ensuring you get your money’s worth. In addition, turning to reliable industry experts like US Window & Door that offer premium products and are committed to seeing their customers satisfied is another stride you can make to ensure you’re getting the quality you deserve.

What to Check to See if the Window Glass Is Tempered

The odds are that you have tempered glass items in at least a few places in your home. However, unless you are purchasing or installing the window glass sheet for the first time, determining if it is annealed or tempered might prove difficult. We know that tempered glass is more durable than regular glass and fractures differently as a result. Toughened glass, unlike conventional glass, fractures into small, even pieces. So, we can say that whacking a tempered glass window with a hammer and watching how it crumbles is a sure-fire way to know if you’ve got a genuine tempered glass window on your hands—just kidding.

identifying tempered window glass

Thankfully, there are less destructive methods to determine if your window glass is tempered or not. There may be various factors behind your decision to purchase tempered glass windows. Perhaps you’re bringing in new windows, or you’re just fascinated by glass furnishings. We can help you in determining if the glass you are installing or already own is tempered, as we have looked at ways to tell tempered glass apart. Tempered glass will always have a few distinguishing characteristics that show it has undergone a rigorous manufacturing process. A couple of these significant characteristics are highlighted below:

Imperfections Don’t Always Point To a Fake

A common misconception is that a flaw on the surface of the glass, such as a scratch or blemish, indicates that it is just everyday glass. On the contrary, imperfections point towards the glass being tempered rather than annealed glass or any other type. Why? As mentioned earlier, toughened glass is subjected to extremely high temperatures during production. At such high temperatures, the glass is pliable. The tongs, which are the instruments used to handle the glass sheets, then leave slight impressions on them that can later be seen on close observation even after the process is long over.

Again, you might notice scratches on the surface. These are caused by the tiny particles created by debris left behind from the tempering process. When the rollers are not adequately cleaned before being heated, small particles melt and fuse to the surface on the side of the glass that is on the rollers. These materials are then dragged over the surface of the glass during regular cleaning, causing scratches. It should be noted that although imperfections are expected to be seen on the surface of toughened glass, the same cannot be said for its edges.

shattered laminated glass

Tempered glass also undergoes a process known as sandblasting. This involves blasting sand particles using pressurized air at the surface of the glass. The process ends up giving the glass edges a smooth finish. Unlike ordinary glass with edges that are relatively rough to touch, toughened glass possesses somewhat rounded, smoothed edges. Looking for imperfections is probably one of the best ways to determine the type of glass once it has already been installed. After all, when a panel of glass is installed in a window, the edges are typically not accessible for inspection, and the manufacturer’s mark may be obscured by the frame or worn out.

Check the Corners for Signs of Etched or Sandblasted Marking

Every sheet of tempered glass is expected to possess a stamp that proves that the glass has been tempered. The stamp is relatively inconspicuous and is usually located in one of the corners of the glass sheet. It serves to display the name of the manufacturer, along with other useful information.

Most importantly, the stamp confirms that the glass is authorized by the Consumer Products Safety Commission (CPSC) for impact resistance. It has to carry the reading “CPSC 16 CFR 1201 CAT II” in accordance with building code regulations. The stamp can be seen as an acid test. This is because if you do not see a stamp on a supposedly tempered glass sheet, the painful yet indisputable truth is that you have purchased a fake.

Score a Line Before Cutting the Window Glass

Scoring a line will require you to cut the glass sheet. Hence, before making use of this technique, you need to be absolutely sure that you want to go through with this decision. Scoring a line on a tempered glass sheet cannot be done with standard tools. A special instrument known as a window-cutting tool is required. This should pose no problem to acquire as you can find it in most hardware stores.

difference between tempered glass and regular glass.jpg

It is recommended that a professional does the cutting. In the case that it is actually tempered glass, attempting to cut it without the proper know-how and the right tools can damage the glass sheet. In a worst-case scenario, you could completely shatter it. 

People mistakenly believe that tempered glass is easier to cut if it is first heated. In reality, heating the tempered glass makes it more malleable and removes the tension from the tempering process, thereby restoring it to its annealed state. At this point, you could cut it, but the glass would no longer have the desirable properties of tempered glass.

Even if you used the recommended window glass cutter, the glass has already lost its safety and impact-resistant qualities and is more likely to break when cut. Rather than getting little bits, this time around, the glass would break into rough shards.

The nature of the incision determines whether or not the glass has been tempered. Once the cut is done and the glass is tempered, it becomes a glistening, uneven surface, with material slivering and flaking off the scoreline. On the other hand, a cut on an annealed glass sheet will look clean and neat. If you have doubts, you may score a line on another glass sheet in which you are already sure of its nature and use it as a point of reference.

Look at It Against the Sun While Wearing Polarized Sunglasses

Another great way of ensuring that you have a genuine tempered glass window is by using polarized glasses. If you have ever worn polarized glasses while in a car, you would observe lines or dots appearing on the car’s windshield or side mirrors. Polarized glasses are designed to polarize or filter out certain types of light. This effect comes in handy when tempered glass is viewed under sunlight using these specialized glasses. Certain features on the glass sheet can be seen that enable you to ascertain its nature.

milgard tempered glass windows

If the glass window has been tempered, you will observe darkened shady lines spread across the glass surface. You may also notice spots on the surface of the sheet. These spots won't be visible to the naked eye, but when you wear polarized glasses, you will see these effects from the tempering process. The rollers will form lines and spots on the glass during the tempering process. 

Final Thoughts

With so many uses for tempered glass all around us, it’s comforting to know that it not only looks nice but also has inbuilt safety measures. Most importantly, these tips will undoubtedly come in handy the next time you go to the store to get a solid and durable piece of glass. We know that no one enjoys paying high prices for inferior products. Hence, we put together this ultimate guide to detecting genuine tempered glass. After all, the safety of your prized possessions, accessories, and home furnishings is more important than anything else.

Say goodbye to wandering salespersons who try to dupe people into buying ordinary, fragile glass! You are now aware that examining the edges, checking for defects, and studying it through polarized glass for distinct lines can help you determine if the glass window in question is genuinely tempered or not. Don’t forget that tempered glass will always have an official stamp or etching to identify it.

US Window & Door takes great pleasure in providing window hardware and accessories and related services such as installation, which are completed quickly and with great care. We have windows and accessories available in conventional or custom sizes and various styles. US Window & Door is one of Southern California’s most reputable and professional window replacement providers. Simply said, we can provide you with a high-quality installation, and of course, provide you with the best the market has to offer. Contact US Window & Door right away, and we’ll take care of the rest!