NationMaster - Encyclopedia: Differential hardening

A differential hardening is a method used in forging swords and knives to increase the hardness of the edge. To achieve this, the edge is cooled more rapidly than the spine by adding an heat insulator to the spine before quencing. Clay or an other material is used for insulation.

This technique is mainly used in katana, the traditional Japanese swords and khukuri, traditional Nepalese knives. Most pieces made with this technique have visible temper line/styles.

Results from FactBites:

Modification of gelatin - Patent 5219992 (3804 words)
	For example, the hardener may be added (a) to the melt containing the modified gelatin, (b) to another gelatin containing layer, (c) to a layer not containing gelatin, or alternatively can be applied in solution or as an overcoat to a previously dried multilayer element.
	The concentrations at which the hardeners according to the invention are required to be used may vary within wide limits and depend mainly on the particular hardening compound used, and the hardness desired.
	After coating, a solution of the vinylsulfonyl hardener (or other hardener or hardeners used in the process) is applied to the outermost coat, and allowed to seep or become imbibed by the gelatin-containing layers.

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