Silicon very avidly grabs ionic oxygen. When you cut glass under water the water rushes in, caps the newly broken bonds, and this packing expands the crack, making it propagate. You cut the glass under mostly neutral pH water.
Because the nature of the cutting stream can be easily modified, waterjets can be used to cut glass for various projects. The most important benefit of the waterjet cutter is its ability to cut glass without interfering with the glass' internal structure.
You'll still need water; however, in this case, you need to have a tray where the glass can lie flat and be submerged to a depth of three inches. Start with a clean, dry piece of glass and use a sharp tool to lightly score the line you want to cut. A diamond blade, such as used in a tile cutter will work too.
Take a capful of the oil and pour it onto the water. Dip the blade in the layer of oil for a few seconds - you'll need to hold the blade at a shallow angle to do this as we only want to heat the oil, and not the water underneath it. You'll then find that the jar is (hopefully!) cut.