There are many types of glass on the market, but only tempered glass is shatter-resistant. But how can you tell if a piece of glass is tempered? Why is tempered glass important? And when should you use it?
To identify tempered glass, look for small dimples or distortions on the surface. You can also view tempered glass in sunlight while wearing polarized lenses and look for stress patterns or a rainbow sheen. Or score a short line in the glass to see if the line is bumpy or irregular.
Let’s look at exactly what tempered glass is, how to tell if a piece of glass is tempered, and some of the ways tempered glass is used. Plus, we’ll answer the question: how much does tempered glass cost?
What is Tempered Glass?
Tempered glass, known as “toughened” or “tempered safety” glass, is produced through controlled thermal or chemical treatments. These treatments alter the strength and toughness of the glass, making it more resistant to breakage and impact.
Making tempered glass involves heating annealed glass to very high temperatures and then cooling it rapidly, which creates internal tension in the glass. So, when tempered glass breaks, it crumbles into small, granular chunks instead of splintering the way float or plate glass breaks into jagged shards.
How is Tempered Glass Made?
There are two primary methods for making tempered glass: chemical tempering and thermal tempering.
Chemical tempering involves using additives such as sodium or potassium salts that are diffused into the surface of the glass during manufacture.
The resulting change in surface tension creates compressive stresses on the surface of the glass and tensile stresses on the inside. This process alters the overall stress balance of the glass, making it more resistant to breakage.
Thermal tempering does not involve additives; instead, it relies on controlled heating and cooling cycles to alter the internal stresses of the glass.
First, they heat the sheet of glass to a temperature between 1150°F and 1400°F, which causes it to soften. Then, the glass is rapidly cooled with pressurized air jets.
This sudden cooling creates tensile stresses on the surface of the glass and compressive stresses on the inside. As with chemical tempering, this process alters the overall stress balance of the glass, making it more resistant to breakage.
Tempered Glass Uses
Tempered glass is most often used where safety is a concern. The most common application for tempered glass is in automobiles—windshields and side windows.
The extra strength provided by tempered glass helps protect occupants in case of an accident, while its resistance to sudden temperature changes prevents windshields from shattering in cold weather.
Because tempered glass is more scratch-resistant, doesn’t absorb UV light like regular glass, and doesn’t deteriorate over time, it is ideal for solar panels and other optical equipment such as camera lenses and telescope mirrors.
Other typical applications for tempered glass include shower doors, building facades, fences, tabletops, electronic device screens, and cookware.
How Can You Visually Tell the Difference Between Glass and Tempered Glass?
When you look at tempered glass with the naked eye, it may be difficult to tell the difference between standard types of glass. However, if you look closely, there are a few small indicators that the glass is tempered.
Here are a few ways to tell the difference:
Inspect the Edges
During the manufacturing process, glass is treated to very high temperatures and sandblasting that leaves a smooth edge on the glass.
If you run your fingers on the edge of a sheet of tempered glass, you will notice it’s not as sharp as regular glass. This is because the tempering process rounds off the edges, giving it a smoother feel.
If you look at the edge of a sheet of tempered glass with a magnifying glass, you will notice its slightly wavy appearance. That is because the edges of the glass are not perfectly flat after the heating and rapid cooling.
Analyze the Corners for a Stamp Identifier
If you can access the corners of the glass, do a close inspection for a stamp. In most cases, tempered glass will have a small symbol that includes the manufacturer’s name and the CPSC (Consumer Product Safety Commission) standards.
If there is no stamp, the glass is probably not tempered. However, some manufacturers do not stamp their products, so the lack of a symbol is not always indicative of regular glass. If you can’t access the corners or there is no stamp, look for other indicators.
Look for Surface Imperfections
Because tempered glass is heated to high temperatures during the tempering process, it is common for slight surface imperfections to form on the glass. For example, tongs used to handle the glass during production can leave marks, dimples, or other distortions on the surface.
If you see these kinds of surface imperfections, it’s a good indication the glass is tempered. However, some manufacturers can produce tempered glass with very few surface imperfections, so this is not always a reliable indicator.
Use Polarized Glasses
Machine rollers create lines, dark spots, stripes, dots, or other subtle blemishes during the tempering process. So, if you wear a pair of polarized glasses while looking at tempered glass in the sunlight, like these Edge Wraparounds (on Amazon), you will notice these areas.
You may also see a rainbow effect over the surface of the glass. These marks are very faint, so you’ll have to look closely.
If you have a piece of polarizing film, you can use that instead. Place the film over your eyes like a pair of glasses, and hold it up to the light. If you see stress patterns or distortions, you can tell if the glass has been tempered.
Score a Line
You can use a window cutting tool to score a line on the glass. Because the surface of tempered glass is brittle, the score mark will be uneven, flaky, or bumpy if the glass is tempered. If the glass is not tempered, the score line will be clean.
However, you should never try to cut tempered glass yourself. The glass can crack and chip easily, so it is best to leave it to the professionals. So if you use this method, make sure to only score a small line on the surface.
How Much Does Tempered Glass Cost?
The tempered glass cost will vary depending on the size and thickness, but you can expect to pay anywhere from $10 to $35 per square foot.
For example, a square foot of 1/8” thick tempered glass will run about $10, while a square foot at 3/4” thickness averages around $55. Keep in mind that the cost of tempered glass will also vary depending on the geographical location and the supplier.
Tinting, custom colors, or cuts will also increase the overall cost of the glass.
Get a quote from a local glass company if you’re considering upgrading to tempered glass. They will give you an accurate estimate based on the size and type of glass you need.