Glass cutter

The cutter, or in some cases the glass, is generously lubricated with light oil or paraffin. Then the cutter is pressed tightly against the glass and a line is scribed with the help of a ruler to form a split in the surface of the glass. This split is referred to as a score. A glass cutter is a hand tool which aids in the cutting of flat or sheet glass.

The score may then be widened by carefully tapping on the opposite side of the glass with a hard tool, but this reduces the smoothness of the broken edge. Finally, the glass is broken along the score. After breaking, the cut edge of the glass is usually polished to smooth the rough edges. 

If the break deviates from the score, the lite can often be salvaged by snapping off the extra glass with a special pair of pliers or using the notches in the glass cutter. Glass thickness also affects the ability to cut and break glass. Generally, thicker glass is more difficult to cut and break. 

Quarter inch plate glass requires considerable strength to break along the score. Extremely thin glass, for example inch glass, behaves differently and will often not follow the score, regardless of the glass cutter's expertise and strictly, the controlled breaking experience.