I have forwarded some thoughts on utsuri here and I want to avoid going too much into metallurgical details with this kantei series. Well, utsuri means “reflection” and refers to a misty and more or less visible reflection in the ji (and sometimes also higher in the shinogi-ji) which is thought to be a hardening effect. The reflection can “shadow” (kage) the hamon, thus also terms like ha-kage (刃景), ha no kage (刃の景), or kage-hamon (景刃文) were in use in earlier times. The dark area between this reflection and the hamon below is called antai (暗帯) and according to the pattern of its appearance, we distuinguish between several different forms of utsuri which allow conclusions on the school (or sometimes even on the smith). Utsuri can be prominent, utsuri ga azayaka ni tatsu (映りが鮮やかに立つ) or utsuri ga senmei ni tatsu (映りが鮮明に立つ), or faint, awai utsuri ga tatsu (淡い映りが立つ) or asaku utsuri ga tatsu (浅く映りが立つ). That means the term tatsu (立つ) means in this context merely that utsuri “is present” and not that it “stands out” as in hada ga tatsu (i.e. “standing-out hada”).
Utsuri is very much a feature of the Bizen tradition and the Facts and Fundamentals of Japanese Swords makes a good point by saying “when you see utsuri there is a 70 percent chance it is a Koto-Bizen work.” Please note that when it comes to utsuri, the term used is an umbrella term that refers to a “whatsoever reflection” on the ji. That means not everything called utsuri is technically and metallurgically the same. In other words, the midare or bô-utsuri seen on Bizen, and the dan-utsuri seen on Aoe blades are quasi “real utsuri” and technically different from appearances like jifu-utsuri, shirake-utsuri, and tsukare-utsuri (疲れ映り) which are addressed as utsuri too due to their reflection-like appearance. Anyway, to see utsuri, a blade has to be in a good polish and you have to examine it under a proper light source. So when you lift up the sword and it is time to check the jigane, focus on the area where the hamon starts and let your eyes wander upwards whilst slowly changing the ange of the blade. Others suggest to hold the blade with the outstretched right arm behind the light source and with the tip facing left and the cutting edge down. But this only works when you have space of course and not at a kantei session where people are handling blades next to each other at a rather close distance. In the following I want to describe in alphabetical order the most common utsuri forms.
bô-utsuri (棒映り) or sugu-utsuri (直映り): A straight utsuri that appears first on hira-zukuri Bizen blades from the end of the Kamakura period (and on shinogi-zukuri Bizen blades somewhat later, towards the end of the Nanbokuchô period). We associate the early bô-utsuri on tantô very much with the Osafune main line and masters like Kagemitsu (景光) and Kanemitsu (兼光) and their direct students whilst the somewhat later bô-utsuri on tachi (or katana) was mostly applied by Ôei-Bizen (応永備前) smiths (e.g. Morimitsu [盛光], Yasumitsu [康光], Moromitsu [師光]) and the smith from the Kozori (小反) group.
botan-utsuri (牡丹映り): Isolated roundish utsuri patches that follow in shape the underlying mokume or itame forging structures. This feature is associated with Osafune Kanemitsu and his direct students like Tomomitsu (倫光) and it is said that botan-utsuri is actually an appearance that occurs when certain areas are polished too much.
chôji-utsuri (丁子映り): Basically a midare-utsuri that shadows a chôji hamon. This term, which is actually a subgenus of midare-utsuri, is not that much in use as it is anyay hard to tell if a flamboyant midare-utsuri seen for example on a Fukuoka-Ichimonji blade is still midare or already chôji.
dan-utsuri (段映り): This term is used when more than one utsuri reflection is seen on a blade, for example a bô and a midare-utsuri, and this feature is usually seen on Aoe blades.
herakage (箆景・ヘラ影) or herakage-utsuri (ヘラ影映り): This term is used to refer to a peculiar utsuri seen on Ko-Niô blades, e.g. by the earlier generations Kiyotsuna (清綱). It appears as about 1 cm long shirake patches that look like spatula (hera) traces, thus the name. The term was introduced by the Hon’ami family which referred in their publications to this kind of reflection as “Niô no herakage.”
jifu-utsuri (地斑映り): – If jifu spots appear all over the blade and form kind of a pattern, the term jifu-utsuri is used, following the aforementioned definition of utsuri as a reflection on the ji. Jifu-utsuri is a rare feature and hardly seen on any blades made later than the Nanbokuchō period. It is for example typical for Ko-Bizen (古備前), Un group (雲), and Aoe (青江) works.
midare-utsuri (乱れ映り): Midare-based utsuri that predates by far bô-utsuri. That means, smiths first produces midare-utsuri and that for quite a while until the Osafune main line smiths changed certain approaches in workmanship and produced towards the end of the Kamakura period a straight bô-utsuri. Please note that a midare-utsuri can also appear on a blade in suguha, that means it is not necessarily a “strict reflection” of the hamon. The Bizen smiths continued to produce midare-utsuri until the mid-Muromachi period but with the then shift towards mass production, it becomes pretty rare whilst it appears at the same time at other schools, like Sue-Seki (末関) and Bungo Takada (豊後高田). With the transition to the shintô era, utsuri again appears on works of smiths that revide the classical Bizen-Ichimonji style, i.e. at the Ishidô school (石堂) in particular and smiths like Tatara Nagayuki (多々良長幸), Tsunemitsu (常光), Tameyasu (為康), Heki Mitsuhira (日置光平), Korekazu (是一), and the Fukuoka-Ishidô smiths Koretsugu (是次) and Moritsugu (守次). But also the early shintô era successors of the Osafune Sukesada (祐定) lineage were able to produce again utsuri. In shinshintô times, midare-utsuri is of course seen at smiths who worked in Bizen style, e.g. Taikei Naotane (大慶直胤), Koyama Munetsugu (固山宗次), Tairyûsai Sôkan (泰龍斎宗寛), and Chôunsai Tsunatoshi (長運斎綱俊).
nie-utsuri (沸映り): When ji-nie forms a concrete pattern, we speak of nie-utsuri. Nie-utsuri only appears on blades in nie-deki or ko-nie-deki and is a typical feature of the Rai school (来). But also great Keichô-shintô and early shintô masters like Horikawa Kunihiro (堀川国広) and Dewa no Daijô Kunimichi (出羽大掾国路) were able to reproduce nie-utsuri. And it is even seen on some blades of Taikei Naotane (大慶直胤).
shirake-utsuri (白け映り・白気映り): In the case whitish shirake areas form utsuri-like patterns, we speak of shirake-utsuri. This feature is associated with swords from Mino but also from Kaga province and other more rural schools like Kongôbyôe (金剛兵衛) and Tsukushi Ryôkai (筑紫了戒) but sometimes it is hard to say if it is just shirake or already a shirake-utsuri. So you might find blades of smiths and schools that are known for shirake being described as showing a shirake-utsuri, for example the Enju (延寿), Naminohira (波平), and Mihara (三原) schools.
tsukare-utsuri (疲れ映り): This is again one of those utsuri that is not really an utsuri in the sense of a midare and bô-utsuri. It describes tired (tsukare) areas in the steel that can appear in a reflection-like manner, mostly after nugui is applied with a new polish.