For the knives of Sakai, the ideal that has won the trust of countless professional chefs is called amakire or "gentle cut". Although the knife can feel soft in the hand after being sharpened on whetstone, it holds its sharpness for a a long time. To achieve this effect, the skill of the bladesmith in charge of the initial forging process, part oft he knife-making process involving multiple craftsmen, is extremely important. The blade of a knife is made from base metal (soft iron) and blade metal (steel). These are heated and struck with a hammer to fold the metals forming the blade.
During the quenching process, the blade is covered in mud to prevent uneven firing. The coated blade is dried and then fired in the furnace at approximately 800 degrees Celsius, and then rapidly cooled in water. This process increases the hardness oft he blade metal. The metal is heated to between 150 and 200 degrees Celsius and then allowed to cool slowly. As the blade cools it forms fine needle-like grain that reduces the chance of any chipping and breakage while the blade is tempered. The bladesmith observes the heat oft he fire visually, and checks the effects of forging by the sound the blade makes when immersed in water. It is said that this skill and experience is what determines the sharpness of the knife.
Forging is followd by a lengthy polishing process that requires approximately 20 steps. To shape the blade, the bladesmith uses both artificial and natural stones to gradually grind the profile, or niku, of the blade thinner and thinner. The bladesmith also occasionally strikes it to remove warping, and achieve the cutting edge. The grind line is then beautifully crafted, and in a process called bokashi (clouding), the base metal portion is rubbed to apply a cloudy matte finish which brings out the hazakai and makes the mirror shine oft he blade portion stand out. It is said that the blade is sure to be sharp when this form is beautiful to the eye.
The handle is attached to complete the knife, a step often carried out by the retailers. The quality oft he knife is also checked during this process. The appearance oft he finished blade evokes both a sense of its sharpness, and a certain quiet profoundness.
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