Bit of techie info ... when you sharpen a blade with a stone or a steel, you produce a burr -- little "filings" that don't completely detach from the metal. You can feel these if you rub a thumb or finger along the edge, like you see in movies -- but take care to move away from the edge, otherwise you'll cut yourself and get nasty steel splinters in your skin. When you strop the blade with soething soft but tough, like leather, you remove the burr without dulling the edge.

Pattern-welded blades, mentioned by Clint Keller above, were made in the days before the composition of steel could be well-controlled. Steel has a carbon content that makes it hard and sharpenable, unlike soft iron which has very little carbon, and unlike cast-iron which has too much carbon. (Confusing, isn't it?) You get the excess carbon out of pig iron by heating it red-hot then beating it with a hammer, which forces out the carbon and other undesirable stuff; if your fire is just right it will burn it off. In Saxon days (for example), it was difficult to produce iron or steel to order: it was pot-luck what you ended up with. So when you'd got enough of each, you'd weld alternate strips of iron & steel together (get them red-hot then hammer them till they fused together); your composite strips could be woven or plaited if desired with others, giving the pattern that appeared on the surface after cleaning & etching. The composite combined the springy hardness of the steel with the toughness and break-resistance of the soft iron. Just like modern composite materials.

Steve