Q: I want to drill holes in glass block. Do you have advice about drills, speed and precautions? - W. Stamp, Longmont, CO
A: Drilling into glass block is not recommended. Sometimes, if the glass gods give you a grin, you can achieve good results using a high-speed drill with diamond-tip bits and water for lubrication. And there are dedicated glass-boring carbide bits that use oil for lubrication. Success often depends on first making a pinhole in the block and then enlarging it to the desired size. But drilling is often unsuccessful because it allows air to rush into the vacuum-sealed block, and the air-pressure change can cause the block to crack or implode.
Depending on how you intend to use the block, Pittsburgh Corning has a product that may offer an alternative: DecoBloc, which is glass block with an oval hole. It's intended for use as a coin bank, flower vase or canister, or you can insert a small light bulb and cord to make it into a light fixture. - HANDY