Instructions
Unlock the Broken Glasses quest. To unlock the quest, you must defeat Gorpus in Manglewood. In addition to unlocking the quest, you will also receive the Earth Sword after you fell Gorpus.
Go to Banon's office in Antheum to accept the Broken Glasses quest. Talk to Banon and ask to go to Roquefort Mine.
Run towards the mine and down the bridge. Defeat the ninjaroids at the bottom of the bridge.
Continue on the path until you come across some pipes. Jump over the pipes and onto the ledge. Defeat the Galvabot on the ledge and drop down the hole in the ground. You will be in a room filled with enemy drillers.
Defeat the enemy drillers in the room. If your focus meter is filled, press the "Circle" button after a driller attacks you to duplicate the attack and learn it for yourself.
Run up the ramp in the room and continue on until you see a hole in the ground. When you see the hole, drop down into it.
Climb up the ladder in the pit. Jump across the platform to the platform in the center. Use your Tremor Thrust attack on the switch in the central platform. To use Tremor Thrust, you must equip the Earth Sword and press the L2 and Triangle buttons at the same time to raise a ladder on the floor below the platforms.
Jump down to the area below and climb the ladder up to a beam. Attack the capsule on the beam to free the blacksmith, Mugwort, trapped inside. This will unlock the blacksmith, and you will be able to modify your swords at Mugwort's blacksmith shop in Antheum.