Use a Diamond drill bit for drilling into very hard tiles (porcelain) and glass.

• Drill at low speed with medium pressure
• DO NOT set the drill on hammer action!
• Swap to a more appropriate type bit for the material behind the tile or glass (masonry/concrete).
• Water cooling will prevent glass from heating up and cracking.
• Start drilling at a 45-degree angle until you have a little grip on the material, then change the drill direction to 90 degrees.
• Drill bits tend to run or wander on smooth surfaces. Minimise this by drilling through pieces of masking tape stuck onto the glass or tile where the hole will be drilled.