We have here an exquisite sword by the father and son (Daisaku) pair of Chounsai Tsunatoshi along with Chounsai Koretosh.  Chonsai Tsunatoshi was the shodai/1st generation name but the father later gave it to his son when he became Chojusai.

Signature reads:
Chounsai Koretoshi
Ansei Rokunen Nigatsu Kichijitsu
Oite Efu Chojusai Tsunatoshi
This sword was made with his son Chounsai Koretoshi and the Mei was inscribed by the father Chounsai Tsunatoshi.

Tsunatoshi’s  family name was Kato  and he was born around 1800. He was the son of Dewa (no) Kuni Kunihide  and he was the younger brother of Kato Tsunahide .  The Kato  family smiths were originally from Yonezawa in Dewa.  Tsunatoshi  was called Kato Hachiro.  He has dated works from around 1823 that he made at Azabu, Edo where he did most of his work.   He received the title of Chounsai in Ansei Gannen (1854).  He handed down this title to his son, Koretoshi of whom he made this sword in conjunction with., in 1856 and took the new title of Chojusai for himself.  It is said that he received a stipend from the Uesugi Clan.  He died at the age of 66 on the fifth day of December 1863.

Tsunatoshi’s sword making group prospered greatly in Edo (Tôkyo).  He and his students greatly excelled in the making of Bizen style swords.  His skill was great enough to surpass the famous sword-making group led by Suishinshi Masahide. One of the most famous of all Shinshintô sword smiths, Koyama Munetsugu, is said in some reference books to have been a student of Chounsai Tsunatoshi.  Others have Koyama Munetsugu  as a contemporary of Chounsai Tsunatoshi and a student of his older brother Kato Tsunahide.  Either way, the closeness of their working styles shows that they were related in some way.   Among Tsunatoshi’s other students were Takahashi Naganobu, Ishido Korekazu, Seiryuken Moritoshi, and others.

There is no doubt that Chounsai Tsunatoshi  was one of the leading sword smiths of the Shinshintô Period.

This sword has some of his most prescious working style in the Bizen tradition. The boshi is beautifully executed as well as the finish of the nakago. The blade is in shirasaya in a pristine polish that was suggested done by Kentaro Yoshikawa.

The mounts are absolutely stunning. The saya is lacquered with a crushed Abolone suspended in lacquer. The mounts are and incredibly detailed Fuchi/Kashira and Tsuba of matching lobsters. So realistic you will be tempted to boil them. The Kodzuka handle is also lobster themed. The tsuka-maki is an off white high level string wrap. The menuki are of copper lobsters also highly detailed. The habaki is gold-foiled as well as the seppa. The sageo is white to match the Tsuka-Ito. The mounts have tsunagi and the sword blade is mounted in a shirasaya. This blade has Tokubetsu Hozon Papers which attest to the skill and  quality of the blade. You will not find another such as this.