To change a small crystal seed or crystal chime back to a crystal saw, go to Brimstail's cave in the Tree Gnome Stronghold and use it on the singing bowl in the western room. The singing bowl can be reached by crossing the crystal bridge to the island in the rift, and it looks a bit like a fountain. Crystal chimes must be in a players inventory or toolbelt when attacking warped terrorbirds or warped tortoises, otherwise they will be immune to all attacks.