玄海正國（Genkai Masakuni），是整個日本廚刀產業中備受推崇的名家之一。作為少數能製作出富士山刃紋本燒（Mt. Fuji Hamon Honyaki）的匠人，一支採用此技術的柳刃（Yanagiba）就可輕易售出數千的價格。玄海正國之名背後，是一位年逾旬的大師——向 米雄（Mukou Yoneo），他曾在堺市磨練技藝，直到四十歲時返回佐賀縣唐津市的gabe島。
此名字的由來可能與地理位置有關，因為玄海町就位於唐津市旁邊。雖然「玄海正國」是向米雄最為人熟知且最常刻於刀身上的名稱，但他所鍛造的刀上亦有署名，一個便是「堺源伯鳳（Sakai Minamoto Hakuhou）」——此為研磨師伯井實（Hakui Minoru）所使用的品牌名。傳統的堺市分工制度，這位大師即使在向米雄遷回佐賀後，仍持續以鍛冶與研磨的夥伴身份密切合作，這種合作關係長達多年，直至伯井實退休為止。
對於了解本燒（Honyaki）刀製作過程的人而言，玄海正國背後所蘊含的技藝水準無需多言。但對那些好奇這些高價刀特性的讀來說，重申一次或許會更有幫助：本燒是一種單一鋼材刀身的熱處理工法，透過在刀背塗上黏土形成絕緣層，再進行淬火，使刃部變硬、刀背保持柔韌，類似過去製作日本刀的方式。「Hon」可大致翻譯為「真正的」、「本質的」，而「Yaki」則與熱處理相關術語有關。合起來，Honyaki 可視為「真正的熱處理工法」，也正說明了此方法在業界中的崇高地位。
對於廚刀用途而言，並不需要柔韌的刀背以防止戰鬥中折斷，因此這種技術主要用來形成所謂的刃紋
The origin of the name might be related to the location, as Genkai-Cho is located right next to Karatsu city. Although Genkai Masakuni is the best known and most often used name/engraving by Mukou san, he has few other names on the blades he forged. One of them is Sakai Minamoto Hakuhou(堺源伯鳳)which is a brand name used by the sharpener Hakui Minoru(伯井 實). Following the traditional division of labour employed in Sakai, these two masters worked closely as the blacksmith and sharpener of each other even after Mukou san moved back to Saga, this collaboration continued for a long time until the retirement of Hakui san.
For those who are aware of the creation process of the Honyaki knife, the level of skill behind the name Genkai Masakuni should need no further explanation. But for people who are curious about the nature of these very pricy knives, it would be helpful to reiterate. The Honyaki process is a heat treatment process of mono steel blades, where the blade is cladded by clay in the spine to form an insulating layer and quenched to have a hardened edge and softer spine, just like how swords were done in the past. The “Hon” can be generally translated as “the real deal”, and “Yaki” is used for heat treatment related terminologies. Together Honyaki can be seen as the real deal heat treatment, which says how highly regarded this method is.
For the intended use of a kitchen knife, it does not require a soft springy spine to prevent breakage in the fight, thus this method is mostly used to achieve a tempering line called Hamon. To create Hamon, a shallow quenching steel must be used with a fast quenching method to form a clear boundary. Often a combination of Hitachi White carbon steel and water quenching(Mizu-Honyaki) is used to achieve a Hamon, but the risk that comes with water quenching is the intense stress build-up in the blade due to different shrinking rate between the area that are covered by the clay and area left exposed. A failed Mizu-honyaki will have a dramatic, explosive failure that breaks the blade in pieces, and this is not uncommon to happen as the quenching temperature is very strict for this to not happen.
Blacksmiths that are trained in this trade for years rely on their eyes to tell the temperature of the blade by the color of the blade, and the heating is done usually in charcoal forge. If that doesn’t sound difficult enough, there is another technique to top it up: Fujiyama Hamon. As the name suggests, the Hamon is shaped like Mt. Fuji on the blade, and having this shape creates a significant point of failure due to the concentrated stress at the Mt. Fuji’s peak where the shape protrudes out the most. For this reason, there are only a few blacksmiths that are skillful enough to produce this Hamon with consistency, and you can count them by one hand.
Genkai Masakuni being one of these master can produce regular wavy hamon as well as the Mt, Fuji Hamon, paired with a mirror finish, the dynamic shape of the Hamon can look like flowing terrain or snow covered mountains, and needless to say, this level of control over a medium that is very difficult to work with has an immense artistic value. With the retirement of Master Ikeda and Master Shiraki, Mukou san too had his retirement in 2020, his blades would continue to be sharpened and polished in the following years but eventually become depleted. But, the name Genkai Masakuni would be remembered and cherished by collectors and knife enthusiasts alike.
