We’ve been told that an experienced craftsman, who has spent time carving Oya stone and creating artistic decorations can tell which mountain (or quarry) a given stone has come from. They can tell how deep in the ground the stone was, and even the direction the stone mine was going just by looking at the stone.

They have memorized the geology of Oya.
They know everything — the stones of which mountains have what qualities, what tools to use, and how to carve them.

It would be fun to take a walk down the streets of Oya with one of these craftsmen, though this is unlikely to happen, as the craftsmen are all very busy.

It makes one want to create a map recording what’s stored inside the heads of the craftsmen. It would no doubt show details of the various buildings, such as what era the stone was from, or which mountain.