Dagger, Persian, 18th century.
© Science Museum / Science & Society Picture Library
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. This dagger has a 'watered' or 'damascened' steel blade, an effect resulting from etching a blade made of steel of varying compositions, providing a suitable combination of properties. The highly skilled art of making such blades was perfected in the Middle East in medieval times.