The process of quenching and tempering is generally called "heat treatment." This process determines the hardness (degree of hardness) and toughness of steel and is the most important process among all the processes requiring skills, experience, and techniques. It is very difficult to take the measure of the steel that we use in the heat treatment, and all the work is carried out by our craftsman's eyes and intuitions.
At our studio, we are particular about using "pine charcoal" when quenching, similarly to the case of Japanese swords, instead of cokes or oil. (Although pine charcoal is expensive, it is essential to create better quality kitchen knife.)