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How to Cut Glass: Scoring, Pressure, and Common Mistakes
Cutting glass is one of the first skills you'll learn when making stained glass. It can also be one of the most frustrating.
Many beginners worry they're pressing too hard, not pressing hard enough, or using the “wrong” tool altogether. The good news is that glass cutting isn't about strength. It's about creating a clean, consistent score line that guides the break exactly where you want it to go.
In this article, you'll learn what a score line is, how much pressure to use, common mistakes to avoid, and a few simple exercises that can help you improve your cutting skills.
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What You'll Need to Cut Stained Glass
Before you begin, you'll need:
- A carbide wheel glass cutter
- A piece of art glass
- Running pliers
- A flat work surface
Carbide wheel cutters are the most commonly recommended cutters for stained glass and fused glass work. Their hardened cutting wheel allows the glass to be scored using less pressure than traditional steel wheel cutters.
If you're using a quality stained glass cutter such as a Toyo Custom Grip Cutter or Toyo Pistol Grip Cutter, you're already using a tool designed specifically for the type of glass used in our hobby.
How to Cut Stained Glass in 5 Steps
At its simplest, cutting stained glass follows the same basic process every time:
- Position the glass securely on your work surface.
- Make a single continuous score from edge to edge.
- Use steady, consistent pressure throughout the score.
- Use running pliers to apply pressure along the score line.
- Inspect the break and repeat as needed.
The quality of the score you create has the greatest impact on whether the glass breaks cleanly and accurately.
What Is a Score Line?
Think of a score as an almost invisible path that we make to basically "tell" the glass where we want it to break.
If you're new to glass cutting, you should know that we don't actually cut glass in the traditional sense of cutting something. Rather, we create a small fissure along the surface of the glass. The cleaner the fissure, the cleaner the break.
The Science Behind Breaking Glass
When placed in the jaws of running pliers, a plain piece of glass that hasn't been scored, will experience tension on the top surface and compression on the bottom. With only a slight bit of pressure on the handles of the running pliers, there isn’t enough localized stress to break the glass.
But once the glass is scored, the equation changes.
Because of this tiny fissure we call a “score,” we have created a point for localized stress to build up along the fissure. It creates a line or crevice where the thickness of the glass is thinner and this allows the glass to break under the same amount of force exerted from the running pliers, which in our last example had no effect on the glass.
So now that we understand what a score is and how it affects the breaking of glass, we can dive into the question of how much pressure is actually needed to create a GOOD score.
How Much Pressure Should You Use When Cutting Glass?
The most commonly asked question about glass cutting is:
"How much pressure should I use when scoring the glass?"
A good score has a clean, almost invisible line and is created using approximately 6 pounds of pressure. (See the practice exercises below.)
If too much pressure is used, the glass crushes rather than creating a clean fissure. Instead of one controlled stress point, you create a series of tiny chips and fractures that make the break less predictable.
A smooth, flowing motion with consistent pressure across the piece will create the most reliable score. Many beginners are surprised by how little pressure is actually required.
What Makes a Good Score?
A good score has a clean and almost invisible line and is often created by about 6 pounds of pressure (roughly .45 Kilograms).
If too much pressure is used, instead of causing a small fissure or separation on the surface, the glass crushes creating a dusty line that is full of little nicks and chips. Instead of having just one stress point to direct your break, each of those little nicks cause additional weakness or stress in the glass making the break less predictable and more likely to go awry.
A smooth flowing motion with consistent pressure across the piece will create the most reliable score. And, you might be surprised at how little pressure is needed to create a good score!
Practice Exercises to Improve Your Scoring
The easiest way to develop proper cutting pressure is through deliberate practice.
Method # 1
Using your bathroom scale can help you determine how hard you need to press to score the glass. Holding a pencil in your hand in a similar fashion to how you hold your cutter and with the eraser pointing downward, press down on the pencil until your scale reads about 6 lb. This will be the approximate amount of pressure you need to use in order to make a good score to cut glass.
Try this a couple of times to become familiar with the amount of force you need to use.
Method # 2
Using your bathroom scale again, place some folded newspaper (this will act as a cushion for your cutter) with a piece of glass on top. Using your cutter on the glass, practice scoring across the sheet of glass while aiming for your scale to read 6 lbs.
This will give you a feel for how hard to press while scoring and whether or not you keep consistent pressure.
Method # 3
For this method, you will need a piece of glass roughly 8 in by 4 in. Cutting the glass across the shortest distance, make a score about an inch from the edge using your normal cutting pressure. Look at your score. Do you see chips? Is it white and dusty or powdery looking? Or does it look smooth and almost invisible? Sometimes you can only see the score if you tilt the glass a little to one side. Now, use your running pliers to break the glass and then look at the 2 raw edges that you just broke. How do they look? They should appear smooth.
Now we're going to repeat this exercise and cut the glass again. Only this time, we're going to do it with a little less pressure. Inspect the score and then run the break. Look at the glass edges again. Did it break easily? Is it smooth?
Repeat the process again with even less pressure to cut the glass. Keep repeating this whole process until you get the lightest pressure for scoring that still breaks cleanly and easily. That’s the correct amount of pressure you will need to cut the glass.
NOTE: This exercise is a great starting point, but it can be difficult to fully grasp without seeing it demonstrated. In my course, I walk through it step-by-step and show exactly how to recognize and correct issues as you go.
More From The Blog - Types of glass cutters for art glass: How to Choose a Glass Cutter
The type of cutter you use, as well as its age and wear, can affect how much pressure is needed to create a good score.
Transparent glass will often cut easier and with less pressure than opalescent glass.
Even different colors will cut slightly differently, and every manufacturer and style of glass will cut differently too.
Common Glass Cutting Mistakes
Even experienced glass artists occasionally struggle with cutting. Here are some of the most common mistakes beginners make.
Pressing Too Hard
The most common mistake is using excessive pressure.
A score line should not be white, dusty, or chipped. Those signs usually indicate that too much pressure is being used.
Inconsistent Pressure
Changing pressure partway through a score can create weak spots that cause the break to wander away from the intended line.
Try to maintain the same pressure from beginning to end.
Judging Pressure by Sound Alone
Sound can be a helpful indicator when scoring glass, but it shouldn't be your primary guide.
Transparent glass often creates more clicking and popping sounds than opalescent glass. If you judge your pressure solely by the sound your cutter makes, you'll often end up pressing too hard on opalescent glass.
Going Back Over a Score
A score should only be made once.
Going back over a score line can create additional fractures and make the break less predictable.
Is the Sound the Glass Cutter Makes a Good Indicator?
Sound can be a helpful indicator when scoring glass, however it shouldn't be your main comparison.
While transparent glass tends to make more of a clicking and popping noise, opalescent glass will often create less sound. If you were judging you're cutting pressure based solely on the noise your cutter makes, you would be pressing much too hard on opalescent glass to create the same amount of sound you would hear while scoring transparent glass.
Why Won't My Glass Break on the Score Line?
If your glass isn't breaking where you want it to, there are several possible causes.
The Score Is Too Light
If the score is too shallow, there may not be enough stress concentration to guide the break.
The Glass Wasn't Properly Run
Even a good score may fail if the running pliers aren't positioned correctly. Quality running pliers can make breaking glass much easier and more predictable.
If you're struggling with this step, read my article on using running pliers and grozing pliers to break glass.
Why Some Glass Cuts Differently
The type of cutter you use, its condition, and the type of glass you're cutting can all affect how much pressure is required. If you're unsure which cutter is right for you, read my guide on choosing a glass cutter.
Transparent glass often cuts more easily than opalescent glass.
Different manufacturers, colours, and textures can also behave differently. As you gain experience, you'll naturally learn to adjust your pressure slightly based on the glass you're working with.
Other Factors That Affect Glass Cutting
The type of cutter you use, its condition, and the type of glass you're cutting can all affect how much pressure is required to create a good score.
A newer cutter will often score more easily than one with a worn cutting wheel. While quality carbide wheel cutters last a long time, they do eventually wear and may require slightly more pressure to achieve the same result. I personally prefer Toyo glass cutters because of their smooth scoring action, Tap Wheel technology and durability. Keeping your cutter lubricated with cutting oil can help it score more consistently and extend wheel life.
The glass itself also plays a role. Transparent glass often cuts more easily and with less pressure than opalescent glass. Textured glass may require additional attention to maintain consistent pressure throughout the score.
Even different colours, manufacturers, and styles of glass can behave slightly differently. As you gain experience, you'll begin to recognize these subtle differences and naturally adjust your cutting pressure to suit the glass you're working with.
The key is to focus on creating a clean, consistent score rather than trying to use exactly the same amount of pressure on every piece of glass.
Frequently Asked Questions
How hard should I press when cutting stained glass?
Many stained glass artists find that approximately 6 pounds of pressure is a useful starting point for learning proper cutting pressure The goal is to create a clean, nearly invisible score line rather than a white, dusty one.
Should a glass score line be visible?
A good score line is often difficult to see unless you tilt the glass and catch the light just right.
Why is my score line white and dusty?
A white or powdery score line usually indicates that too much pressure is being used. A good score should be clean and subtle rather than bright white or chipped looking.
Can you score glass twice?
No. Scoring the same line a second time often creates additional fractures and makes the break less predictable.
Why won't my glass break where I scored it?
Common causes include inconsistent pressure, scoring too lightly, scoring too heavily, or improper use of running pliers.
Understanding the concepts behind glass cutting is important, but many beginners still struggle because they're not quite sure what a good score line should actually look like.
Seeing the process demonstrated and explained clearly can make it much easier to recognize the difference between too much pressure, too little pressure, and a clean score that will break reliably.
Looking for more ways to improve your results? Read these next:
Ready to Improve Your Glass Cutting?
Reading about glass cutting is helpful, but seeing exactly how much pressure to use and how a good score should look can make a huge difference.
In my Cutting Stained Glass Made Easy course, I walk you through the entire process step-by-step and show you exactly what to look for when scoring, breaking, and troubleshooting glass. It's designed to help you build confidence and improve your results faster.
About the author
I’ve just finished reading about cutting, and I can tell I’ve been cutting to hard, (closer to running a jackhammer hah). Hopefully it won’t take long to correct it. Thanks so much for you help.
What about running the cutter off the edge of the glass. Will that ruin the cutter?
It can. Although the cutting wheels are pretty tough, I always try to prevent smashing them into the table surface. If the surface is wood, it will usually dent the wood but a harder surface or repetitive strikes would likely cause damage over time. To check if your cutting wheel is damaged, do a nice light score on window glass. The line should be smooth and continuous. If you see skips in the line, it’s best to replace the cutting head.
Merci! Je vient de comprendre mes erreurs .