Karach (Chaos Matter in the Githzerai tongue) is a transmuting metal used in making magical items. It is smelted from the chaos stuff that leaks through the ever-changing gate to Limbo in Xaos. Only the most dedicated of smiths can force the stuff to remain stable, so the smelters and workshops of these craftsmen are usually unchanged from visit to visit, even in the continually-changing burg of Xaos.