Honyaki

Honyaki heat treatment relies on a single steel blade with differential heat treatment as opposed to san-mai or clad and layered construction. Each blade is coated with clay prior to quenching, with a thicker layer along the spine. This causes the spine section of the blade to cool at a slower rate to a higher temperature during the quench, giving the blade more resilience along the spine. The clay is often applied in decorative patterns for aesthetic appeal. 

Mizu Honyaki, or water quench honyaki makes for the hardest possible edge but due to the rapid heat loss during the quench, it has a high failure/fracture rate even for experienced smiths. Abura Honyaki, or oil quench honyaki also makes for a very hard edge but the heat loss happens at a slower rate to a higher temperature resulting in lower failure rate but less hardness than mizu honyaki.

Honyaki knives typically have higher edge performance in reference to sharpenability, edge retention and finish due to their very high hardness. They are typically not suited for first-time users of Japanese knives as they require a certain level of skill and technique to avoid chipping and otherwise damaging the very hard cutting edge. High quality wooden cutting boards are best and hand wash and hand drying is required. The knives will take on a patina with use but will rust is left dirty or wet.