The shape of the edge on a blade is also called its "grind". There is always a tradeoff between a blade's ability to ake a sharp edge and its ability to retain an edge. The way a blade cuts is by focusing the various forces exerted on it to a very high pressure on the edge. The finer the edge, the more focused the force. That is why a blade is "sharp".
Edges differ also in whether they are symmetrical around the vertical centerline of the blade, whether the taper to the edge is short or long, and whether the taper is convex, straight or concave. Each type of edge yields a blade with different cutting properties.
The particular type of grind found on any given blade depends on multiple factors:
- Individual preferences of the user, including whether the blade will be used in left or right hand;
- The purpose of the blade, e.g., kitchen use versus clearing brush versus battlefield weapon;
- The type(s) of steel used; harder steels can be sharper, but they are also more brittle while softer steels are tougher but do not take a fine edge. This relationship is complex and sometimes hardness and toughness can both be achieved;
- Cultural norms; certain kinds of edged weapons have a style dictated by cultural factors as well as more pragmatic concerns;
- Skill of the blade smith; some edges are relatively easy to fashion and others require considerable skill.
See also the excellent article on blade geometric properties by Patrick Kelly, "Understanding Blade Properties"
The various types of edge features can be combined in many variations.
Examples of edge types
1. Hollow Grind: Yields a very sharp but weak edge that requires frequent sharpening.
2. Flat Grind: Sharp, but like #1, also less durable.
3. Sabre Grind: Long lasting edge at expense of sharpness. Often found on knives from Scandinavia such as the puukko.
4. Chisel Grind: The edge is ground on one side only. Many ethnographic knives of interest have chisel grinds. The side which is beveled is important for the particular use and which hand will hold the blade.
5. Double Bevel or Compound Bevel: Similar to the Sabre Grind except with multiple bevels at the edge ande behind. Improves cutting ability but more importantly, stability since the blade will resist rolling from one side to the other.
6. Convex Grind or "Axe Grind": Opposite of #1. Makes for a very strong edge. This is difficult grind to make and requires considerable skill.
Another excellent resource is Knife Edge Grind Types. Some additional variations are described there.