Knives are at least 2.5 million years old and still evolving
Stone cutting tools from the Oldowan culture show that people have been making knives for at least 2.5 million years. Blades have since moved from flint and obsidian through copper, bronze and steel to ceramic and titanium, each material trading sharpness against toughness and resistance to rust.
The word comes from the Old Norse knifr, meaning knife or dirk. Early blades were wood, bone or stone; improved metallurgy brought copper, bronze, iron and eventually steel. Uses multiplied accordingly, from hunting and combat knives to pocketknives, chef's knives, cleavers, steak knives and ceremonial blades such as the Sikh kirpan.
Each part of a knife has a name. The spine is its thickest section, opposite the edge on a single-edged blade; a fuller is an optional groove that lightens the blade; the ricasso is a flat area where blade meets guard; and the tang extends into the handle, either part way, as a stick tang, or along its full length. Antique Brazilian knives such as the Sorocaban used a method called enterçado, riveting a recycled blade to a bladeless handle.
Material choices involve compromises. Carbon steel takes a keen edge and sharpens easily but rusts and stains, while stainless steel, alloyed with chromium and often nickel and molybdenum, resists corrosion but cannot get quite as sharp. Laminated blades sandwich hard, brittle steel between tougher layers, though the exposed edge can still corrode, and Damascus steel welds different steels together and works them into patterns. Ceramic stays sharp for years without upkeep but snaps if dropped or twisted and needs silicon carbide abrasives to hone.
Steel blades are either forged, hammered or pressed while hot, or shaped by grinding away stock; both are then hardened by heating past a critical point and quenching, and tempered to relieve stress. An integral bolster often signals a forged kitchen knife. Flat grinds taper steadily and hold up well; hollow grinds are thinner and slice shallow cuts better but bind in deep ones. Holes drilled in blades cut friction, allow one-handed opening of pocketknives, or let butchers hang their tools.
Source: Knife
