How to Use the Crucible to Make Lava and Obsidian

Setting up the Crucible

Place your Crucible on top of a heat source. Common heat sources include torches, lava, campfires, or magma blocks — check JEI for what your version accepts. The Crucible must sit directly above the heat block. Once placed correctly, it will slowly melt certain solid blocks into lava.

What to melt

Cobblestone, gravel, and stone are typical inputs. Right-click the Crucible with the material to add it. Over time it converts to lava inside. When full enough, right-click with a bucket to extract the lava. You can also pipe fluids in and out if you have fluid pipes from other mods.

Making obsidian and other fluids

Pour water into a Crucible that already contains lava (or vice versa) to create Obsidian — this is one of the few ways to get obsidian without a diamond pickaxe in skyblock-style play. Some Crucible variants (like Blazing Archwood Crucible or Cascading Archwood Crucible) have special behaviors — the Blazing variant may work without external heat, while the Cascading variant may handle fluids differently. Check each variant's tooltip in-game. Water in a Crucible can also be used for crafting or piped into barrels for composting.