There are two types of shakuhachi, jinashi and jiari (地無し and 地在り). Historically, the first types of shakuhachi were jinashi while jiari came about much later, around the beginning of the 20th century. Jinashi shakuhachi are completely or mostly natural on the inside while jiari shakuhachi are mostly or completely plaster or glue on the inside. This plaster or glue is used to literally sculpt or cast the desired sound. As a result, many jiari tend to sound more like Western concert flutes.
Ultimately, quality jiari shakuhachi are easier to make because a predetermined bore shape is often cast or formed inside of the bamboo and the length is adjusted via joints. Conversely, Jinashi are much harder to craft at a high level because of the difficulty in acquiring madaké bamboo with ideal dimensions and due to the higher level of skill that’s required to work more with the bamboo. But when done expertly, jinashi shakuhachi can offer an entirely unequaled experience.
The first individual to be credited with augmenting the inner bore of a shakuhachi with ji-paste was a “Grandmaster” of the shakuhachi named Araki Chikuo, aka Kodo II (1823-1908). Additionally, ubcategories of jinashi such as hochiku (法竹 aka hotchiku or hocchiku) and Kyotaku. Hochiku were created by Ishibashi Gudo at the request of master Watazumi (1910-1992). They tend to be much longer and larger on the inside than the jinashi that were used by the Komuso monks of the Edo period. Kyotaku are also longer bass shakuhachi which follow certain specific criteria such as having all the holes in a straight line and of a smaller size. These were invented by Nishimura Koku. Lastly, these longer bass shakuhachi inspired various “spiritual successors” such as Ken LeCosse’s large Taimu or “big nothing”.