The characteristic of swords in this period is that swordsmiths made attempt to make blades using the methods of Koto time. The characteristic of Shinshinto is that the "waves" in its hamon start from the machi like Koto, but contrary to the vast majority of Shinto hamon that started in a straight line from the machi and then became curved. Boshi are also waved if the hamon on the blade waved, maintaining a sort of matching style all to the hamon. These swords are shiner than the previous ones, and the jihada doesn't appear clearly, giving a less eye-catching look.
First Half of Shinshinto (1764-1829)
As Sukehiro and Shinkai were highly praised by Kamada Natae in his book written in this period, many swordsmiths began to imitate their works, making strong toran-ha (billowing) shape in the hamon. Swords in this period imitated the Osaka style. Then Masahide (one of the most famous Shinshinto swordsmiths) advocated in his book that "we should make swords by the method of Koto time." With this final target, swordsmiths began to create their own steels, trying to reach the quality of the ancient ones. Combining materials which have different quantity of carbon, a good jihada will appear. Therefore, swordsmiths used a lot of materials like old nails to adjust the quantity of carbon to be suitable for swordmaking. Even today this steel is called oroshigane. An easy way to produce tamahagane was available during Shinto, and swordsmiths could get good-quality tamahagane. Therefore, it seems that most of them didn't make their own oroshigane. But some smiths like Kotetsu followed Masahide's suggestions and reached a top-quality level combining ancuient iron/steel with modern one. In effect, ko-tetsu means "ancient steel."
Latter half of Shinshinto (1830 - 1868)
Until around 1868, swords which emphasized mighty shape were made in this period. The mihaba is wide and the length is longer then the previous period's. They often look like the the tachi in Nambokucho. Swordsmiths tried to reproduce the Koto sword, but after 1868, important political changes occurred, and the production and quality of swords were highly affected. The Tokugawa Shogunate finally fell after more than 250 years, and Emperor Meiji took power, and thus began the time of modernization known as the Meiji restoration.
JAPANESE SWORD SOCIETY OF HAWAII 2011