Sumi (墨) is Japanese for black ink. Although there are many different kinds of sumi, only a few are suitable for tattooing. The sumi made by Kobaien in Nara City is considered the highest quality and commands a high price. Sakurazumi (桜墨 "Cherry Blossom Ink"), baikaboku (梅花墨 "Plum Flower Ink") and itsutsuboshi (五つ星 "Five Stars") are the makes of Kobaien sumi that are most commonly used for tebori tattooing. Kobaien sumi is made by collecting the soot from burning pure vegetable oil—usually sesame or pauwlonia—and combining this with a glue derived from vegetable starch. This is shaped into sticks and dried. When needed, the tattoo artist grinds the stick in a slate inkwell called a suzuri until the correct consistency is achieved.
Recently in the West, bottles of black tattoo ink have been sold labelled as "sumi ink," although it is difficult to believe that this is Japanese sumi ink. Real sumi is perishable and cannot be stored for longer than a day or two, and the price of making 500ml of ink from real dry sumi would far outstrip the retailer's asking price (high quality brands such as Itsutsuboshi cost over $100 per 3-inch stick).
Although older master artists and those taught in the traditional way still use sumi for tebori tattooing, younger Japanese artists and those who tattoo in the Western style generally use ready-made Western tattoo ink.