The kratonite warhammer is an item that can only be obtained and used while training Dungeoneering. It may be picked up from the table at the beginning of a dungeon, obtained as a monster drop, or produced using the Smithing skill.
A kratonite bar is a bar of refined Kratonium ore. It can be created through the Smithing skill by using kratonium ore on a furnace, requiring level 30 Smithing and granting Smithing experience. The kratonium ore itself can be mined from the rocks scattered throughout the dungeon, obtained as a monster drop, or bought from the Smuggler.