To make a straight cut in a piece of glass, hold a straightedge along the line to be cut. Dip the wheel of a glass cutter into kerosene or light machine oil. Hold the cutter between your index and middle fingers and brace it with your thumb. Stand and lean over the glass for more freedom of movement. Press the cutter wheel down at the far edge of the glass and move the cutter toward you along the straightedge, applying firm, even pressure. (You should hear a sound like radio static.) Score in one continuous motion, ending after the cutter comes off the glass.
Wearing gloves, pick up the glass as shown; break it along the score. Using even pressure, gently push the glass down and outward with your thumbs and up and outward with your fingers. Steadily increase the pressure until the glass snaps in two. To snap off a narrow piece, grasp it with special breaking pliers or with slip-nose pliers.
To cut a curve, draw it on the glass with a grease pencil (you can trace it around a cardboard pattern), then score freehand just inside the line. Break the glass as you would for a straight cut, with your hands pointing in the direction of the curve. If the glass won’t snap, tap the score gently on the back with the ball end of the cutter, then try again. Cut a sharp curve in stages, removing as much excess glass as possible with straight or gently curved cuts before cutting the final curves. Wearing safety goggles, remove rough edges with special grozing pliers or with needle-nose pliers.