Hamon is a traditional Japanese technique used in the forging of blades, particularly in the creation of katana. It refers to the visible line that appears on the blade, which is a result of differential hardening. This process involves heating the blade and then quenching it in water or oil, creating a hard edge and a softer spine, enhancing both durability and flexibility. The hamon pattern varies depending on the specific techniques and materials used by the swordsmith. Different styles of hamon can indicate the quality and craftsmanship of the blade, making it an important aspect of Japanese swordmaking and a point of interest for collectors and enthusiasts.