This tatto design is based on Celctic Art, drawn by black 0.5 mm pen. 

Celtic tattoo designs are not only utilized by the cultural arts, they have become more and more popular amongst mainstream populations. Celtic Knotwork is probably the best known style of Celtic design. The intertwined patterns of never-ending lines appealed to the Celts, symbolizing their ideas of eternal life and the intricate relationship of humanity with both the divine and the natural worlds.