Bizen Province has been acknowledged to be the kuni which has produced the most master swordsmiths since ancient times, creating the most top-quality blades from the early Kamakura era through the Muromachi era. Some of the reasons for this were that Bizen was blessed with an abundance of the raw materials that are the building blocks of great swords: i.e. sources of pure water and high-quality sand iron. The two rivers, Yoshiigawa (吉井川) and Asahigawa (旭川) ran through the heart of the Bizen Osafune area providing ample sources of both pure water and high quality sand iron.
Bizen Province was the largest sword production center of the Muromachi period, but due to political and economic changes that took place in the Momoyama era and coupled with the flooding of the Yoshii River that runs through the Osafune region, it was almost entirely obliterated by the end of the 16th century. Particularly disastrous for the local swordsmiths was the Tenshô 19 (1591) flood of the Yoshii River after which only Yokoyama Tôshirô Sukesada (横山藤四郎祐定) and a few other masters survived. Accordingly, hardly any dated Bizen blades from the Bunroku (1592-1596) and Keichô (1596-1615) eras are extant. The flood not only deprived this area of most of its sword-smith population, it also decimated the natural resources so crucial to the industry.
Sword making was revived some time during the Genna era (1615-1624) by Yokoyama Tôshirô Sukesada (横山藤四郎祐定) and his sons, Shichibei no Jô Sukesada (七兵衛尉祐定), Genzaemon no Jô Sukesada (源左衛門尉祐定), and Sôzaemon no Jô Sukesada (宗左衛門尉祐定), whose lineages continued to exist for the rest of the Edo period.
Shichibei no Jô Sukesada (七兵衛尉祐定),who called himself the fifth-generation smith from the line of Yosozaemon no Jô Sukesada (与三左衛門尉佐定), was born in the fifth year of Tenshô (1577) and died in the second year of Enpô (1674) at the age of 98. His existing dated blades start with the second year of Genna (1616) and this shows us that he was active until about the age of 80. Throughout his long life Shichibei no Jô Sukesada (七兵衛尉祐定) saw the prosperity, the downfall, and the revival of Bizen Osafune as a production center for blades, and he is usually credited with successfully connecting Sue-Bizen with the shintô era of sword making.
Kôzuke no Daijô Sukesada (横山上野大掾祐定) was the son of Shichibei no Jô Sukesada (七兵衛尉祐定)and was active around the Jôo (1652-1655), Meireki (1655-1658), Manji (1658-1661), and Kanbun (1661-1673) eras. He was born in the tenth year of Kan-ei (1633), his first name was Heibei (平兵衛) and he died in the sixth year of Kyôhô (1721) at the age of 89. He is regarded as the best and most representative Bizen Osafune smith of the Shintô period. From the time he received the title of Kôzuke no Daijô in 1664, he signed his works using that title in his signature. Before that time, however, details about his life are somewhat limited. This might be because when he was born in 1633, his father was already 57 years old. When he began his sword making under his father’s tutelage, he spent much of his time making daisaku blades for his father.
In the fourth year of Kanbun (1664) at age 32, Sukesada received the honorary title of Kôzuke Daijô and, according to his personal auto-biography (Sukesada Ki 祐定記), he had an audience with the first generation Daimyô of the Okayama fief, Ikeda Mitsumasa (池田光政, 1609-1682). This was the first honorary title that was given to a Bizen Osafune swordsmith in the Edo period. After this auspicious occasion, Sukesada started to make swords to be offered to shrines within the Okayama fief.
He continued to make quite a few shrine dedication blades over his lifetime, many having an unusually long nagasa. The longest that I have come across was the earliest known example which was dated the sixth year of Kanbun (1666) and dedicated to the Kibitsuhiko-jinja (吉備津彦神社). It had a nagasa of 120.3 cm or 47.36 inches and weighed 1,800 grams or about 4 pounds. It still resides in the shrine today.
We have dated examples of his work from Kanbun (1661) until the time of his death in the 6th year of Kyôhô (1721). Therefore, he embraced the stylistic changes from the Kanbun and Enpô eras (1661-1673) through the Teikyo and Genroku eras (1684-1704). He made same Kanbun shintô sugata with a shallow sori and normal mi-haba as well as blades with a less tapering sugata with a deep sori and extended chu-kissaki in accordance with the tastes of the Genroku era. Most of his surviving blades show the sugata of the Genroku era and occasionally he made blades with a noticeably thick kasane.
In the second year of Enpô (1674), Kôzuke Daijô Sukesada’s (横山上野大掾祐定) father, Shichibei no Jô Sukesada (七兵衛尉祐定) passed away at the age of 98. At that time, Kôzuke Daijô was 41 years of age. From around the Jôkyô era (1684-1688), we see daimei blades made together with his younger brother, Shishinoshin Sukenobu (七之進祐信) whom Kôzuke Daijô Sukesada’s (横山上野大掾祐定)later adopted and made his successor. Sukenobu changed his name to Sukesada and late in his career (the sixth year of Shôtoku, 1716), he became Yamato Daijô Sukesada (大和上野祐定). Yamato Daijô Sukesada (大和上野祐定) supported Kôzuke Daijô Sukesada throughout the last thirty years of Kôzuke Daijô’s career. Since the receipt of the Yamato Daijô title and his subsequent succession took place late in his career, signed works in his own name are quite rare. There is no doubt, however, that judging from gassaku blades that exist his work was very close in skill level to that of his father, Kôzuke Daijô Sukesada.
Here are some basic characteristics of Yokoyama Kôzuke Daijô Sukesada (横山上野大掾祐定).
SUGATA: His blades were mostly katana and wakizashi. Tachi and tantô are rare and a few naginataand ken also exist. Most of his blades are shinogi-zukuri with an iroi-mune but we occasionally also see hira-zukuri blades and blades with mitsu-mune. Unlike the prevailing Kanbun-shintô sugata of his time with their shallow sori, Sukesada’s blades show a tendency towards koshi-zori and feature some funbari. These are unique traits that go back to his roots in the Bizen tradition.
JITETSU: Densely forged itame that will be partially mixed with mokume. More refined works show an even finer, beautifully forged ko-itame, but utsuri or other activities within the ji are often lacking. A characteristic feature of Kôzuke Daijô Sukesada is that most of his works show a clear mizukage near the machi.
HAMON: Generally, a midareba or suguha in nioi-deki with ko-nie appearing along the habuchi in both cases. The nioi-guchi is bright and clear, but there are few hataraki within the ha. Most of the suguha are of an excellent deki done in chu-suguha. His focus, however, was midareba that he formed in a very distinctive pattern. All his midareba start with a sugu-yakidashi. The yakidashi shows similarities to an Ôsaka style yakidashi, because it widens as it connects with the hamon. This can be somewhat mis-leading during kantei. His hamon tends to start relatively low at the base becoming wider from the mid-blade section up to the kissaki. There exist also flamboyant midareba where certain elements of the hareach the shinogi.
Kôzuke Daijô Sukesada formed a unique gunome where the gunome elements are arranged in groups of four with a distinct wide tani (valley) separating the groups of four. Close inspection will also reveal that the “groups of four” are really comprised of two groups of double gunome (fukushiki-gunome) that are separated by a smaller and shallower tani(valley). This hamon style of fukushiki-gunome relates back to the hamon of the Sue-Bizen blades from the Muromachi era and is not found in the works of either Kôzuke Daijô’s father, Shichibei no Jô Sukesada, nor his successor, Yamato Daijô Sukesada.
The next point of note is the yakigashira of the gunome. Yakigashira is the term used for the top (or head) of the gunome. The yakigashira of Kôzuke Daijô Sukesada’s earlier works will be roundish while his later works will often be more of a togari-ba shape (peaked). Sometimes a blade will start out with one form and then transition into the other. An alternative name for this type of fukushiki-gunome with peaked yakigashira will be kani-no-tsume (crab claws).
BÔSHI: The bôshi usually has a ko-maru shape and some are midare-komi with a pointed return. Any kaeri will tend to be short.
HORIMONO: Elaborate horimono cannot be found. On a rare occasion simple bô-hi can be found.
NAKAGO: The nakago will have a somewhat bulbous kurijiri and a shallow katte-sagari yasurimei.
MEI: Kôzuke Daijô Sukesada (上野大掾祐定) signed with a thick chisel in a deep and powerful but careful manner. The characters followed the printed style of writing (kaisho) and were chiseled on the sashi-omote side towards the nakago-mune. He usually wrote Yokoyama Kôzuke no Daijô Fujiwara Sukesada (横山上野大掾藤原祐定).Dates, if included, will be on the ura. On occasion he used a split mei putting his place of residence, Bishû Osafune Jû (備州住), on the ura side. With “offering” swords (dedicated to temples and shrines), however, the full signature including his place of residence was signed in one line on the haki-omote sides with the date on the haki-ura side.
Another interesting point about his signature was his use of non-usual interpretations of certain characters. This is an important kantei point since there are so many gimei swords with his signature. Here are some examples; the character Yoko (横) in Yokoyama is executed with the left hand radical (才) instead of (木). The character for jô (掾) in Daijô is written with the top right radical (ヨ) instead of (互). The character Bi (備) in Bizen is written with the right part of the character using (⼡) and (用) instead of using (艹), (厂), and (用). Finally, he wrote the character fune (船) in Osafune with the right part (公) instead of (㕣).
Only Kôzuke Daijô Sukesada wrote with these variations as presented above. When his son, Yamato Daijô Sukesada (大和上野祐定)signed his father’s name on daisaku blades, he did not use any of these variations. Instead he signed the character for Suke (祐) with the left hand radical (⺬) instead of (⺭). Apart from that, Yamato Daijô Sukesada signed his father’s name in one row on the haki-omote and the date on the haki-ura side and, for whatever reason, did not add the family name Yokoyama to the mei.
Sato Hirosuke, Tôken Bijutsu 751 (August 2019) A Study on Yokoyama Kôzuke Daijô Fujiwara Sukesada
Kokan Nagayama, The Connoisseur’s Book of Japanese Swords
Honma Kunzan, Nihontô Meikan
Nihontô Koza, Shintô Volume
 A Daisaku blade is a blade that is made by the student under the master’s guidance that is signed by the master. It is regarded as being shôshin.
 A daimei blade is a blade with the student smith signing his master’s name on to a blade made by the master himself. It is regarded as being shôshin.
 Gassaku blade is a joint effort by two or more smiths (often a student and master) and signed by both smiths.