Source: In common use
Nie (沸) literally means "seethe" or "boil." In Japanese sword connoisseurship, it is the name of larger martensite crystals that appear on the polished surface of some traditionally made Japanese swords, which sometimes look like bubbles of boiling water rising to the surface. Nie mostly forms along the temperline, but on some swords is also seen on the blade's surfaces.
Abundant nie on a 14th century sword of the Sōshū tradition.
Hard but brittle martensite is formed when steel with a high carbon content is heated to a high temperature and then rapidly cooled, and carbon gets trapped in a crystal state.1 The forming of the larger nie crystals is achieved by heating the steel to an unusually high temperature before quenching.
While most cultures had ways to create martensite-rich edges, the deliberate forming of structures of larger martensite crystals is seem uniquely Japanese. All the other tricks, forge folding, differential hardening, and the forming of a hamon were more widespread.
While the special heat treatment creates the nie crystals, the preparation of the steel and the thermic clay applied before quenching determine where they appear. While many Japanese smiths played with it, it is the Sōshū tradition that is the most well known for its artistic use of nie.
1. For the science behind it, see: www.metallurgyfordummies.com.
Nie & nioi
When the crystals are so small that the naked eye cannot make them out individually, and they appear like a whitish mist, it is called nioi (匂), literally "fragrance". Nioi is present to some extent on all blades, but when no or very little nie is present, we speak of nioi-deki (匂出来). When the work shows nie throughout, we call it nie deki (沸出来) where deki means workmanship or interpretation.
The misty temperline on a Bizen sword in nioi-deki.
Made by Yosōzaemon jo Sukesada in 1523.
Sold by Mandarin Mansion in 2021.
The grainy nie particles on a Sōshū sword in nie-deki.
Attributed to Tametsugu, active in the 14th century.
Mandarin Mansion inventory 2022.
Manifestations of nie
Nie can manifest itself in different shapes and structures that all have names. One could compare them to brush strokes on paintings, some effects are only seen on the better swords, while others can be indicative of poor workmanship. But on the whole, when judging a blade, we are looking at how deliberate the various effects appear to be formed, which tells us the amount of control this smith exerted over his work.
The presence of nie itself often says more about the tradition in which the blade is forged than the quality. Many fine Bizen swords, for example, are made in nioi-deki. Moving to Sōshū work, there has to be nie, and lots of it, for a blade to do that school justice. When a sword has a lot of nie, it is called nie-atsushi (沸厚し), literally “thick nie”, often translated as "plenty of nie".
In the basis, nie can appear as small particles, ko-nie (小沸), regular nie, or ara-nie (荒沸), coarse or large nie crystals. Ara nie can be indicative of poor work when isolated, but when present all over the blade, it's a feature. Go Yoshihiro, one of Japan's best smiths, is known for well-controlled ara-nie. When there are irregular patches of nie, they are called mura-nie (叢沸), "clump of nie" which are often not intended by the smith.
Nie in the yakiba (焼刃) "hardened edge":
Nie will usually mostly appear along the temperline, the demarcation between hardened steel and the ji (地), which is the surface above the hamon (刃文).
Ha-nie (刃沸) is nie that formed in the hardened area of the sword, the area between temperline and edge.
Hotsure (ほつれ / 解れ) are arrangements of nie that make the temperline look like a frayed piece of cloth.
Kuzure (崩れ) are deformed parts of a nie-based hamon usually seen at irregular hamon that diverge considerably from the forging lines in the steel. Also referred to as nie-kuzure (沸崩れ) or yaki-kuzure (焼き崩れ).
Kinsuji (金筋), literally "golden line," are short, straight, glassy black lines of nie that appear inside the hamon. Usually near the temperline.
Inazuma (稲妻), "lightning" are similar to kinsuji but crooked, resembling lightning strikes.
Sunagashi (砂流し), “flowing sand.” Flowing lines of nie that resemble brushed sand, usually following the general line of the hamon.
Nie in the ji:
Ji-nie (地沸), nie crystals that appear in the ji.
Chikei (地景) are black lines in the ji. They can be black gleaming lines of ji-nie that appear merged toghether, like kinsuji but appearing in the ji instead of the yakiba. The term is also used for dark lines in the ji-hada (地肌) grain of the steel in the ji.
Jifu (地斑) are spots of dense ji-nie that do not follow the pattern of the grain.
Yubashiri (湯走り), “running hot water.” Formations of ji-nie with a somewhat transparent look and borders that are not very clear.
Appreciating Japanese swords is a little like wine tasting; there's often a hint of this, a hint of that. The better quality pieces will have more outspoken and very deliberate "notes." How one interprets what one sees in a blade is partly subjective, and different experts may give slightly different descriptions of the same blade. Demarcations between, for example, nie and ko-nie are not exact.
Here are some examples of nie on different blades I've had through my hands and what I am seeing:
Horikawa school work in ko-nie-deki with lots of ji-nie. Sunagashi can also be seen.
Sōshū school work with coarse ara-nie, lots of ji-nie, ha-nie, and prominent sunagashi.
The above terms appear in many sword publications, but to me, the most useful has been Markus Sesko; Encyclopedia of Japanese Swords. Lulu Enterprises, Inc. 2014. Available from Lulu.com. Also important for the study of Japanese sword are Sesko's authoritative Kantei Series where he goes more in-depth on the different features.
Another valuable resource is Kōkan Nagayama; The Connoisseurs Book Of Japanese Swords. Kodansha America, Inc. 1997.