You sell the Alloy Box and buy an Arm Mold.

SK: “Molds are a nice thing to work with! When creating items, you can place things that fit in them, and then put the Mold in the Cauldron! That will create an item that fits the mold with the items inserted! Also, to make a piece, you need to fill out all of an area covered.”

MM: “Thanks for the info!”

You go back to your Cauldron.