Instructions
Go to Marleybone and find Felicia Worthington in the Regent's Square. Speak to her and purchase the Transmute Diamond Card from her for 200 gold. You can earn 200 gold by doing quests and selling the drops of monsters and bosses such as Jade Oni or Krokopatra.
Head to the furniture shop in Marleybone. Purchase the Treasure Card Crafting Table. You can also purchase the crafting table in the furniture shop of Mooshu.
Travel to the Shoshun Village, Jade Palace. Head to the eastern exit of the village to reach the Cave of Solitude. Mine the ore deposits until you have 15 ores. You need to transmute 15 ores for every diamond you want to create.
Click on the icon of a treasure card on your crafting table. Select the Transmute Diamond Card in the list and your character will use the ores in your inventory to create a diamond. Each diamond will take five seconds to cool down. A newly made diamond must cool down before you can make another.