Things You'll Need
Pumice hammer stone
Obsidian is a naturally occurring form of extrusive igneous rock formed from felsic lava deposits in the vicinity of volcanoes. It is characterized by a glasslike composition that is very hard and very brittle, fracturing off in pieces that are extremely sharp when subjected to external force. As such, it can be difficult and hazardous to carve obsidian with any kind of precision. However, with the right tools and preparation, you can make the job easier on yourself.
Put on your protective eyewear and gloves to protect yourself from stray shards.
Place the obsidian stone on a table, work bench, or similar surface. Prepare the large flat surfaces of obsidian by striking them with your pumice hammer stone to smooth them out. Apply short, sharp glancing blows across the surface of the obsidian rather than striking directly downward for the best results.
Use your knapping tool to make the precision cuts in your stone. Apply direct hits to the surfaces you prepared in Step 2 to remove the unwanted sections of your stone until you have the final shape you desire. Knapping tools will remove the stone in very small flakes, so this step will take a significant amount of time.
Apply epoxy around the cornered edges of your finished stone to smooth them, allowing you and anyone else who handles the stone to avoid inadvertently cutting themselves.