You can use Diamonds to refine yellow equipment and above.
Normal Refining (free refining chances every hour) and Advanced Refining (strong effects and require spending Diamonds).
Refreshes the equipment's additional skill (level will increase or remain unchanged, but will change the type of skill).
Yellow equips can have a maximum of 1 skill, with a max level of 2
Red equips can have a maximum of 2 skills, with a max level of 3. Red equips can also have 3 skills after having the secret one from refining.
Purple equips can have a maximum of 3 abilities, with a max level of 5. Purple equips can have 4 skills after having the secret one from refining.
Unlocking Secret Ability
Defeating "Ormer" unlocks the "secret skills" technology at level 52. Maxing and matching the skills of fine equipment of red quality or higher unlocks the "Secret Skill Effect".