Star metal: 2 x star metal ore; 1 brimstone; 1 black ice in a furnace. Star metal is found in meteorites that land between the Mounds of the Dead and Frost Temple - black ice is found in the same area.
Obsidian: 10 x obsidian and 1 steel bar in the forge at the Well of Skelos. Obsidian can be found in the volcano.