Wherever there's a customer, a blacksmith will be there! Just summon the master smith's spirit...
The Smith Spirit is a mystical item that cals forth the power of a blacksmith whenever needed. It is given by Zappa to Serge in Termina (Home World), who can use it on the Overworld and at Save Points. It allows the forging of the highest level equipment in the game, including Rainbow weapons and armor.
For more information, see Rainbow Equipment.
For the shop, please keep in mind that Iron and Steel equipment disappear after the Dead Sea and are replaced by Stone equipment. Additionally, after Rainbow Equipment becomes available, it replaces Silver and Mythril equipment.
From: Key Items (Chrono Cross)