All forms of are applied by hand, using wooden handles and metal needles attached via silk thread. This method also requires special ink known as ink (also called ); tattooing practiced by both the Ainu people and the Ryukyuan people uses ink derived from the indigo plant. is a painful and time-consuming process, practiced by a limited number of specialists known as . typically have one or more apprentices working for them, whose apprenticeship can last for a long time period; historically, were admired as figures of bravery and roguish sex appeal.