There are two different type of Irezumi: Nuki-Bori and Gaku-bori.
NUKI-Bori Singular design, without any background.
GAKU-Bori Tattoo design with a background – surrounding patterns which includes secondary elements such as rocks, waves, water or wind-bars, clouds, flowers etc.
The name “Gaku-bori” can be literally translated as ‘framed tattoo’(Gaku 額 is “framed”, Bori 彫り is “tattoo”). Gaku-bori has specific shapes and names depending on a part of the body and always formed by Mikiri – boundary between tattooed skin and bare skin. There are few different types of Mikiri(Akebono Mikiri, Botan Mikiri, etc.) depending on the boundary type. Decision on what exactly type of Mikiri can be used in tattoo project normally made considering the way it could be connected to the new tattoo pieces in future.
Because of human body anatomical aspects, Gakubori is only possible to be arranged independently on arms and a back. Tattoos on all other body parts like legs, rib sides, middle chest etc. can be only done as Nuki-Bori, not ‘framed’ – without any Mikiri, or can be connected to Gakubori existed on the other body parts which already have Mikiri.
Gaku-bori is truly the most important part of traditional Japanese tattoos, and quality of the whole work depends on it’s quality.