How To Run A Scored Piece Of Stained Glass

There are several methods of "running a score" that are used by stained glass artisans.

Once you have scored a piece of glass, your next step is to "run the score" and break the piece out.

When you begin scoring a cut, always start it a little bit in from the edge of the glass.  When you end the score, you
always roll the cutter over the edge of the glass.   

The best place to start running the score is always on the edge of the glass that you ended the score line at.   This
ensures that the scored piece breaks out easily and cleanly.

Here are a few universal techniques for running a score that are used at one time or another
by almost every stained glass artisan.

The fastest method used by most experienced artisans to run a score is to use your hands.
Make a fist with both hands and grab the glass on both sides of the score line with your thumbs up.

Next, pull your hands apart and snap the glass up and out, just like you would snap a wooden twig.

Your index fingers underneath each side of the score line and your thumbs on top of the glass are used to exert the
pressure that breaks apart the glass.

For large longer pieces that weigh more, rest the heaviest part of the glass on your work surface in case you accidently
drop the glass after it separates.

This technique is expecially useful when you are working with many small cuts and where speed is of the essence.

How to Use Your Running Pliers


Running pliers should always be used with the adjusting screw facing upwards.  

The black line or indentation that is in the center of the top jaw should be centered on the score line you intend to run. 
If your running pliers doesn't have a center line, draw one on with a magic marker or scribe.

Line up the jaw of the running pliers with the center line of the score and place them about half way up the edge of the
glass.   

Gently squeeze the pliers together until you hear the glass click or snap.

Short score lines will break apart immediately.  

On longer score lines you will need to repeat the process at the other end of the score until the glass separates.

Sometimes you will need to repeat the process a couple of times, but normally the glass will separate with only one or
two squeezes.

Don't squish down too hard on the running pliers or you will crunch the glass edges.

It is important to remember that running pliers need to be adjusted for different glass thicknesses.

Instead of using your hands, you can use breaking pliers to run a score line.

There are basically two types of breaking pliers.  Those with smooth or serrated flat jaws and those with smooth or
serrated curved jaws.



Both types work as long as you remember to place the flat jaw on top of the glass when running a score.

If you're right handed, hold the glass with your left hand and place the jaws of the breaking pliers next to the score. 
Snap the piece off by pulling down with the pliers and your left hand at the same time, just as you would using your
hands in the first scenario.

For small pieces, use two pairs of pliers to snap the pieces apart.

Whenever you run a score make sure you pull the pieces apart as you make your snap.

A pencil, nail or any other small diameter object can be used to run a score line.

Just place the pencil directly underneath the score line and quickly press the glass down on both sides of the score at
the same time.

This method achieves a clean break every time and works well on all glass thicknesses.   Just increase the diameter of the
nail as the thickness of the glass you are running increases.

You can use any relatively thick straight edge to run a long score line including a paint stirring stick.

Just place the straight edge directly under the entire length of the score line and quickly press down on the glass, on both
sides of the straight edge.

This method works just like a pencil or nail, except it is preferred for longer score lines.  You can use any object that is about
1/8" thick to run a score using this technique.

This technique is used by professional glass companies for running long straight scores on larger pieces of glass such
as window panes.  

After you have scored the glass, pull the piece so the score line is about 1/4" from the edge of the table, hold the glass
firmly with both hands, lift it a few inches from the table and quickly bring it down over the edge of the table to snap it.

You need to jerk the glass down hard over the edge of the table, so don't be overly cautious.  On the other hand, don't
 slam the glass down so hard that you can't control the break.

Make sure that the score line is not directly on the edge or just over the edge of the table. This could result in an uneven
break with possible jagged edges.

There are times when no matter what running technique you use, a piece of glass will just not separate.  

When this happens it's time to try this technique.

Don't press too hard along the back of the score or you will get an wanted break.

This technique lends itself especially well to circles.