It is said that his master student Naomasa helped his master in the last decade. But it's not sure that Naotane passed away and some tales telling us that he is still forging Kanemitsu blades..
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Kataoka Ginsaku wrote in his short biographie that Naotane's oldest work dated Kansei 13th year (1801). He was 23 years old.
When he was over 70 years old ( Koka 2 1845) he started a five year long journey continue to make many swords. So he was a physically strong person and it's possible that he worked until his dying day..
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Daimyo procession pdf by Constantine N. Vaporis
http://www.bakumatsu.ru/lib/Constantine_N._Vaporis_Lordly_Pageantry_The_Daimyo_Procession_and_Political_Authority.pdf
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I read in some book, the three plants are known as three friends in bad cold weather. They withstand the cold standing for:
healhty and longevous, upright and unyielding or honest and clean..
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