Things You'll Need
Diamond or carbide-tipped drill bit
Personal protective equipment (gloves, eye protection, etc.)
Glass insulators have become obsolete for their intended purpose, with the introduction of more sophisticated technology and underground lines. They still exist in significant numbers, though, in antique stores and among collectors. Insulators can be used for light shades, suncatchers, salt and pepper shakers or other arts and crafts. Many of the crafts that use glass insulators require holes to be drilled in the glass, a specialized process that takes time and care.
Use putty to make a circle, about 1/4-inch deep, around the area you intend to drill. Press the putty onto the glass. This needs to be watertight.
Fill the putty "dam" with turpentine. This will help keep the bit from getting hot and will reduce chipping.
Fit your drill with a glass-drilling bit (usually diamond or carbide) of the size you want the hole to be. You may be more successful if you use a small bit first, then work up to the size you want. This allows the bit to grind a bigger hole without putting extreme pressure on the glass.
Drill the hole. A drill press works the best because it will make a straight hole. Use constant pressure, but go slowly. Allow the bit to grind its way in gradually. Too much force on the drill will break the insulator.
Clean the putty and turpentine off and smooth any rough edges with a fine file.
Always wear proper protection when cutting glass. Use a face or eye protector and leather gloves. Wear a long-sleeved shirt.