Testing your Scoring pressure

 Most often people are asked to listen to the sound of scoring.  Unfortunately, different glass styles make different sounds. Float glass makes a particular sound, transparent stained glass makes a slightly different one, and opalescent glass makes almost no sound. Consistent pressure of the right amount is important to the clean breaking of glass. Therefore, we must learn to cut with the same consistent pressure on all types of glass, rather than listening for sound.

It is easy to tell when the scoring is too heavy.  A white line shows along the score.

The heavy score line near the break shows the white line and the irregular break

It is not so easy to tell if the score is too light or just right.

A heavy score in the distance and a lighter score nearer

Pressure

The general recommendations for the pressure to use during scoring is 4.5 – 7 Lbs or 2 – 3 Kg. This is difficult to judge. I found that I needed a means of letting people know for themselves the pressure they were exerting. It is not enough to watch and say that was too hard, that was too soft, etc.

My method of teaching novices how to judge the pressure they are using is to use a digital kitchen scale that can have the scale set to zero. Place a piece of glass no larger than the platform on top of the scales. Zero the scale display.  Have someone watch the scale display while you score in your usual way. Of course, you must not touch the glass with your other hand. Have them tell you the maximum and minimum weights displayed. Keep repeating until you can consistently use that 4.5 – 6.5 pounds (2 - 3Kg) pressure.

The testing setup showing a heavy score on the right and the start of a 1.9kg score on the left.

Consistency

The other important element of scoring is to keep the pressure consistent throughout the score. This test will also show how evenly you apply the pressure during the score. The objective of scoring is to use the correct pressure throughout the length of the score. If your pressure varies significantly during the score, it will be difficult to get the glass to break consistently along the score line. Because the amount of weakness in the surface created by the score is variable.

Your observer can tell you when the pressure is less than optimum or more than desired.  If the pressure variation has a reasonably consistent place in scoring - such as at the beginning, or on a curve - you can fix it. Concentrate on correcting the fall off in pressure. For example, most people start off with a lighter pressure than further into the score.  Getting the feel of the correct pressure will enable you to apply it right from the start of the score. Sometimes, people increase the scoring pressure when they come to curves. This test will show if that is true for you.

This curve was scored with 4.3kg pressure showing that heavy pressure can result in break outs from the score line

This testing can take quite a while. But it is worth the time spent in getting the scoring pressure right to reduce the number of unwanted breaks. However, it is not a one-time test. When I begin to have difficulties in breaking glass, I go back to this test to check whether I am scoring too heavily. In my scoring practice, I find that my best ones are those with 1.8 to 2.5kg (4.0 to 5.5 pounds) with the cutter I use.  This is less than many, but it has worked well for me for years.

There are, of course, other elements that go to making a good score and break. But the most important thing in scoring and breaking opalescent glass is to avoid too heavy a score by listening for a sound. Cut to a consistent pressure whatever sound is heard.