Wrought iron is commercially pure iron, having a very small carbon content (carbon content does not exceed 0.15 percent), but usually contains some slag. It is tough, malleable, ductile and can be easily welded. However, it is too soft to make blades and swords, or at least for their cutting edges, which need to be made of steel with a higher carbon content.
Common usage is for 'wrought iron' to mean iron of this composition. However, strictly, it should be confined to iron that has been wrought (i.e. worked) into a finished product. The unwrought commodity is according to its form 'bar iron', 'rod iron', etc. Wrought iron has been used for thousands of years, and represents the "iron" that is referred to throughout history.
Ornamental ironwork is often referred to as "wrought iron," even though today it is more likely to be made from mild steel.
Wrought iron is rarely completely pure. It is a fibrous material with many strands of slag mixed into the metal. These slag inclusions give it a "grain" like wood, and distinct look when etched. Also due to the slag, it has a fibrous look when broken or bent past its failure point.
The fibers of wrought iron gives it some interesting properties, however. Hammering a piece of wrought iron cold causes the fibers to become packed tighter, which makes the iron both brittle and hard. As wrought iron lacks the carbon content necessary for tempering, it is believed that cultures that never discovered how to make steel would cold work wrought iron tools in order to harden them.