The Nihon Bijutsu Tōken Hozon Kyokai (日本美術刀剣保存協会) (NBTHK) or Society for the Preservation of Japanese Art Swords is an agency of the Japanese government whose remit is the registration and preservation of antique swords. The NBTHK is also responsible for the Japanese Sword Museum in Tokyo.
The Japanese Cultural Affairs Agency founded the NBTHK in 1948 but the rating system for antique swords was renewed in 1980. There are four levels of classification in this recent system:
The first two are a lower level certification, while the last two are held in high esteem, as very difficult to obtain. Juyō Tōken certificates are issued only once a year.
There are also Juyō tōken certificates dated before 1980, as the reform had only affected the lower grade papers (Kicho, Tokubetsu Kicho and Koshu Tokubetsu Kicho). The first Juyō Tōken papers were in fact issued in 1951; these were the highest ratings attainable by a sword until 1972, when the NBTHK introduced Tokubetsu Juyō Tōken.
Similarly to what happens in other fields in Japan, like martial arts, the process of obtaining higher ranked papers involves applying for lower ranked papers and then after achieving them, applying for the next one up; each application must be paid for, and if the application is successful an additional fee is charged.
A sword rated Juyō Tōken will receive a hand written certificate and will be published by NBTHK in the Juyō Tōken Nado Zufu, with a full description an a oshigata, a drawing that shows the activities of the blade. A cut out page of this publication is generally enclosed together with the certificate.
Some numbers: there are about two million blades registered in Japan and only 11,000 (0.5,5%)
have been rated juyō, while as few as 1000 are tokubetsu juyō.