Persian dagger with curved blade of watered steel, 18th century.

The manufacturing of steel was carefully studied and extensively documented by Islamic scientists. By varying its composition, and with suitable heat treatment, steel may be made soft and tough, springy, or hard and able to retain a hard edge. In a weapon, a combination of these properties is desirable. At the time of the Crusades, the Europeans were struck by the quality of steel blades used by the Moslems. Many blades were made of a 'watered' or 'damascened' steel, an effect resulting from etching a blade made of steel of varying compositions, providing a blade which could bend without snapping, and would hold a keen edge. The highly skilled art of making such steel probably originated in Persia, and was perfected in Damascus in medieval times.