The Key To A Perfect Scoreline

A perfect scoreline makes EVERYTHING easier. But how much pressure should you use when you make a score on the glass?

This is a question that I get asked a LOT, so I decided to make a video with a useful Pressure Test for you to try.

It’s worth remembering that each sheet of glass needs slightly different pressure applied. Some will make the ‘sssssh’ sound and some – like Bullseye opaques for example – don’t make a noise at all.

perfect scoreline in glass


If you’re having trouble with your cutting accuracy there are lots of tips you can learn to help you get better.

If you don’t have a local class my Conquering Curves course has taught lots of people the skills to cut glass accurately. And not only accurately but without excess effort. How nice is that!
The class is self-paced and online so you can learn these cutting tricks even if you are unable to get to a class. You can find out more about it here: Conquering Curves.


Take the Pressure Test

So it’s a good idea to try this Pressure Test out when your project includes a new type of stained glass that you haven’t cut before. Cut a small piece off and test away! It will give you a feel for how that particular glass responds and how much pressure you need to apply for a perfect scoreline.

In the long run you’ll cut more accurately and waste less glass.

Glass Cutting Checklist

I could blind you with the science of wheel sizes, angles and the mechanics of force but I don’t think that’s what you need. Rather you need a simple cutting checklist to help you along.

  • Stand up to cut if you can
    This will help you maintain consistent pressure along the whole score. The optimum height for your cutting table is somewhere between your hips and waist
  • The cutter wheel must be rolling freely
    Check before you start scoring
  • Different brands of glass, different thickness and different colours behave… differently!
    Cut off a small piece of any new-to-you glass to see how it behaves. It will save you glass in the long run
  • Keep your cutter perpendicular to the glass
    Don’t lean to the left or to the right as this results in an angled break. A perfect scoreline gives a straight break.
  • Keep an EVEN pressure throughout the length of the score
    If the pressure varies the depth of the fissure will vary and the glass will break randomly instead of along the score line
  • A score that will result in a good, strong and clean edge is practically invisible from the surface of the glass
    You should see it if you look at the glass from an angle
    A white line is indicative of a gouge rather than a true fissure. This is the result of pressing too hard and will not give a good break – the edge will be chipped and weak
  • The depth of the fissure is linked to the speed of the cut. The faster the wheel rolls, the deeper the cut
    If you’re speedy, don’t press so hard! If you’re slower, press harder. There’s no ‘right’ and ‘wrong’ – you might cut a straight line quickly and lightly and a difficult shape slowly, pressing harder.
    Consistency of pressure is the key
  • I’m assuming you know not to run along a score twice?
    This will gouge or crush the glass, it won’t break cleanly and it will ruin your precious cutter wheel. You can go across a score, just not along it.
  • It may not be you!
    There are – very, VERY occasionally – sheets of glass that simply misbehave. This is normally due to insufficient annealing (cooling down). This happens less and less these days but it’s worth being aware of as a possibility.

Summing Up Cutting Glass Pressure

Author Joseph Farrell put it brilliantly: “The secret of all power is – save your force.”

Get creating that perfect scoreline. Watch the 3 minute video above and take the Pressure Test!

Go here for a list of my other cutting glass tutorials – there are lots of them 🙂

53 thoughts on “The Key To A Perfect Scoreline”

    • If you treat them well – don’t press too hard, maintain them well, don’t go over scores a second time and don’t use them every minute of every day they’ll last years.
      If you don’t treat them well it could be a matter of months.
      Irregular score lines that don’t cut cleanly are a tell tale sign of a wheel that needs changing.
      It’s one of those ‘long as a piece of string’ questions, Robert but I hope that helps some 🙂

      Reply
  1. Thank you so much for sharing your knowledge and experience. I have found your information very helpful and it reassures me of practices I am doing right and makes me more aware of what I need to work on.

    Reply
  2. If I’m getting these emails on a regular basis am I to assume that I am signed up or is this another group of information? I just want to make sure but also not duplicate my membership. Thanks, Bud

    Reply
  3. Hi Milly, I’m your latest member…I need all the help possible…With your help I’m sure I will learn very quick…Tony in Florida

    Reply
  4. I haven’t looked at the link for all your glass cutting tutorials, but wondered if you have one on cutting textured glass, like ripple and herringbone?
    Thank you so much.
    Thanks,
    Naomi Fron

    Reply
    • Isn’t it Judy?!! Once you start applying the same method to art glass you’ll start to notice the difference to wastage.

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    • Using a ruler or a strip cutter is best Ferne. That way you’ll get a nice straight line. If it’s a diamond with a long thin point, use the breaker-grozer pliers to tease the end open so that you don’t snap the point off.

      Reply
  5. Hi,just signed up to receive your tips & info. I’m new to stained glass but having a bit of trouble with foiling for some reason. Sometimes I Can’t get it perfectly centered so I don’t know if,when I go to solder it,the pieces won’t be attached properly. What am I doing wrong?

    Reply
    • You can try using lined paper as a guide for the foil until you get the hang of it. If you’re making a stained glass sun catcher or a panel that has foiled edges, start foiling on the part of the glass shape that is internal; in other words, try to avoid the foil meeting itself on the outside edge of the piece. I hope that helps. Thanks for your question Kaye.

      Reply
  6. I am so glad I found your site! I took stained glass classes about twenty years ago but never kept at it due to children, many moves and lack of space. Now that I have room and a designated area to work in I have been working on small projects. It has been frustrating because I have pretty much forgotten everything I learned way back when! I know I have been pressing to hard while cutting and will definitely take the pressure test. I have a question about my cutter. I bought a pistol grip thinking it would be easier for me. While I do like it, I have a problem with the cutting oil coming out when I press down to cut a piece. It makes a big, wet mess. Any ideas of what could be causing this?

    Reply
    • Oil will leak from cutters, especially these ones. You can try storing it in a jar wheel up but the best solution is to put some oil on a bit of sponge in a jar and dip the cutter in every few cuts. Not fill the cavity with oil at all. That way you have more control of the oil and definitely less mess. I hope that helps.
      Welcome back to stained glass Pam 🙂

      Reply
  7. Great info for a newbie! Thank you! My biggest problem is w imperfections in the glass (pock marks and cuts). The wheels gets stuck or skips and it’s hard to control when it hits one. Am I getting poor quality glass or is this the norm? Any tips for negotiating the glass terrain?

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  8. Hi Milly.
    I havn’t done glass in 20 yrs and forgot most everything. I’m so thrilled to find you. Thank you for all your help

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  9. Yep – I’m guilty of pressing too hard. Now I know why I get those teeny weeny chips along the cut line sometimes . Thank you for the tip.

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    • Hi Dale, glad you’ve isolated a possible problem before it takes hold. These things have a habit of adding up and making stained glass more difficult than it should be.

      Reply
  10. Hi Milly.
    I am relatively new to stained glass work, I have enjoyed your video hints and tips and hope there are more to come. After watching them I am hoping to cut more accurately and not spend so much time grinding. Thanks Milly.
    Jenny.

    Reply
    • Hi Jenny, thanks for your kind comments. There’s nothing wrong with grinding but it does save time and grinder bits if you can cut neatly and use the grozer pliers. Good luck with the cutting!

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  11. Thank you for this video. I do have trouble with the pressures I apply on different types of glass. It sometimes is to the point that I have to stop because my arm is so tired. I will keep practicing, and making, and enjoying each piece because I am so hooked on this. I am so proud of each piece when I am done. Thank you Millie for your tips.
    A stained glass artist in the making,
    Martina Brown

    Reply
    • Hi Martina, That pride that we get when we keep going and then succeed is the best feeling. You should be proud, it’s not the easiest craft but it is the absolute BEST 🙂
      I’m glad the video helps. Hopefully you’ll be able to work out how hard to press for each type of glass… it takes a while to build up experience so this is a good quick guide. Good luck, Milly

      Reply

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