Cutting is the skill everything else depends on. Pieces that fit well are easy to foil or lead, while badly cut pieces cause gaps, stress and weak joints. The method is the same for every colour of glass: score once, then break along the score.
Before the first cut
- Practise on cheap clear window glass until scoring becomes automatic.
- Work on a flat, firm, clean bench. A sheet of cardboard or a cutting mat beneath the glass stops it sliding.
- Wear safety glasses. Glass splinters can fly at the moment of breaking.
- Draw the cut line on the smooth side. Textured glass is scored on the flatter, smoother face.
- Put a drop of cutting oil on the wheel, or check the reservoir of an oil-filled cutter.
Scoring
- Hold the cutter upright between the first two fingers and thumb, or like a pen. There is no single correct grip, so use whichever lets the cutter stay vertical.
- Place the wheel just inside the edge of the glass and press firmly with even pressure.
- Push the cutter in one continuous stroke from edge to edge without stopping. A pause partway often shows up as a break at that point.
- Listen as the cutter moves. A steady, quiet scratching sound means the score is good. A crunchy sound and a white powdery line mean too much pressure.
- Never go back over a score. Doing so damages the wheel and does not improve the break. If a score fails, make a fresh one beside it.
Breaking straight lines
After scoring, the glass is brought to the break straight away. There are three common ways.
- By hand. Place the thumbs on either side of the score, parallel to it, and roll the wrists outward as if opening a book.
- With breaking pliers. Grip the glass with the jaws either side of the score and twist gently. This gives even pressure and suits thicker glass.
- With running pliers. Line up the mark on the jaw with the score and squeeze lightly. The break runs along the line.
Curves
Shallow curves usually break by hand once the score is made. If the glass resists, tap gently along the underside of the score with the ball end of the cutter until the score appears to run, then ease the pieces apart.
Deep curves are harder, and are best practised on scrap. Cut the hardest curve first while there is still plenty of surrounding glass to hold. Relief cuts, which are short extra scores running from the waste toward the main curve, let the waste fall away in stages. The waste is then nibbled away with grozing pliers, working slowly towards the line.
Avoid designs with very sharp inside corners or near-right-angle internal shapes. Glass tends to crack from these points and the finished panel is weaker.
Grozing and finishing the edge
Hold the piece firmly and use grozing pliers to take off small nibbles, a little at a time. Small edge chips and rough ridges can be knocked back with the serrated jaw of the pliers. The edge is then smoothed on a grinder or carborundum stone.
Common faults
- The glass shatters or breaks off line. Usually too much pressure, or a piece scored where it was already stressed.
- The break happens where the cutter stopped or lifted. Score in one unbroken stroke.
- The score will not run. Too little pressure, or the wheel is worn or dry.
- A ragged white line. Pressure too high or the wheel is damaged.
- Pieces do not fit the pattern. Cut slightly outside the line and grind back rather than trying to hit the line first time.
In this section
- Glass Tools and Equipment
- How to Cut Glass
- How to Grind Glass and Apply Copper Foil
- How to Solder
- How to Make a Leaded Panel
- How to Cut Lead Came
- Working Safely With Glass
Terms used here are explained in the Glass Glossary, and the Learn section covers the history and types of glass.