Cutting glass without a glass cutter can be achieved by either using string, metal or scissors. Water is necessary for all three methods, and protective eyeware and gloves should be used.
Prepare a bucket of water large enough to submerge the glass up to your elbow. Put on the safety goggles and gloves. Dip the string in rubbing alcohol and squeeze dry. Tie the string tight around the glass where the cut is to be made.
Light the string on fire and immediately plunge the glass into water up to your elbow.
Strike the glass below the line where you wish to make the break using a wooden stick. Having the glass submerged up to your elbow will help with vibrations from the strike. Make sure to wear slip-resistant gloves to avoid abrasions.
Prepare a bucked of cold water wide enough the submerge the glass laying flat; the water should be about 2 to 3 inches deep. Put on safety goggles and gloves. Scratch the glass with an abrasion tool or file in the shape of the cut.
Shape the wire along the line of the cut with extra wire as a handle. Heat up the wire until it is red hot and place along the abrasion line.
Immediately place the glass in the cold water until the water barely covers the top surface of the glass. The glass should break cleanly.
Prepare a bucket of water large enough to submerge the glass completely with room enough to have your hands in the bucket. Put on goggles and gloves.
Submerge the glass completely under water and cut the glass how you would paper. The edges will not be as neat as other methods, but sizing down glass can be achieved.
Use a torch to smooth out the rough edges of the glass. Make sure to wear the safety goggles and gloves and follow the instructions for operating the torch.
Working with glass is very dangerous, so always wear the proper safety attire.