Glass Cutting Lesson

My sister, who used to own a stained glass shop, gave me a lesson in glass cutting.

• You want a flat, clean surface. You can lay down a towel or piece of carpet if you like, but this is optional if your surface is clean and flat
• She uses a commercial grade glass cutter that dispenses oil, but she also showed me good results with a hardware store version. There is oil made for the purpose available at art stores, but you can just use light machine oil. Dip the cutter wheel in the oil and dab off the excess before each cut.
• We used a straight edge (actually a drywall square) with pieces of 220 grit PSA sanding disks stuck to its bottom so the square wouldn't move. You must be careful not to move the square by sliding it or the glass will scratch.
• Note the amount of offset between the wheel and the side of the cutter, and allow for it when you set your straight edge.
• Hold the cutter in your hand between your first and second fingers. The handle sticks up between your first and second fingers and rests in the crotch between them.
• Critical to a good cut is holding the cutter vertically left to right. She told me that if you let your cutter lean one way or the other, the glass won't break squarely, and the cut edge will be sharper. Also, hold it nearly vertical front to rear.
• Begin, and end, the cut 1⁄8" from the edges. The glass may not break properly if the score line extends to the edges.
• As you make your cut, apply pressure to the cutter and move it in a smooth motion away from you along the straight edge. You have the right amount of pressure when you can hear the glass scritching and a visible score is made. Again, start and stop 1⁄8" from the edge of the glass.
• She says, and indeed I have found, that pushing the cutter across the glass makes it easier to get a good score. One fluid motion works best.
• To hold the glass for breaking, first make two fists. Bring your hands together and point your thumbs down and away so they are pointing directly away from you and they are parallel. You will hold the scored glass between your thumbs under the glass and your curled fingers on top, with the score between your hands. Gently bend the glass about the axis of the score line. You don't want to break it in one motion. Instead, you want to rock it back and forth until you see and hear the glass fracturing along your score line. The fracture will progress with each bend until the glass finally separates.

You can clean up any sharp edges with the same stones you sharpen tools with, or even by rubbing them on a polished concrete floor. With some elbow grease, you can grind a nice edge suitable for a display case.