Trying to Cut Glass

by Andy
(Michgan)

After I score the glass and use running pliers it breaks away from the score line. Why does this happen and how can I keep it from happening again.

Answer
Hi Andy,

I think that when you are scoring the glass you are either not using enough pressure or you're using way too much pressure.

You want to see a score line, but you don't want to see a white line or bits of glass flying up as you score. When I say "see a score line", that is sometimes hard to do. Run your fingernail over the area you just scored. You should be able to feel an indentation in the glass.

It takes about 5 lbs. of pressure to get a good score. The way I have always taught my students to tell when they are using the right amount of pressure is to use a piece of scrap window glass. With the first score, press as hard as you can. That will show you what not to do. You will see the white line and bits of glass flying up as you score. Try running the score. Chances are that will not break along the score line.

After that little excercise, keep scoring and breaking, using less and less pressure until you get to the score that again does not break along the score line. Do one more score using slightly more pressure. If it breaks along the line, you have found the right amount of pressure to use.

The more you practice, the more proficient you will get at cutting glass. It does take practice, just as every technique in stained glass work takes practice.

Not every type of glass will score and break with the same pressure. Red glass, which actually has gold in it, takes more pressure. Red is followed by orange and yellow in hardness. Any glass that has white in it will take more pressure. Blues and greens are the easiest to cut. Cathedral glass is slightly easier to cut than opalescent. None of those glasses are impossible to cut, and all of them are used every day. It's just that some take more pressure than others, and there is a learning curve to know when to use more pressure and when to use less. However, my initial statement should be applied to all of them. You never want to see a solid white line with bits of glass flying up as you score.

One other point, make sure you are cutting on the smoothest side of the glass. That will make a difference in the way the glass scores and breaks.

I hope this will help you with your glass cutting. If you haven't read my glass cutting tips and techniques, go to Cutting Glass. You might find something there that will also help you.