Fukurin

Scale wrap. It is the cuticle of the skin which appears as a line drawn in a ring around a scale. This name was taken from the term Fuku (meaning to 'cover' or 'wrap') and Rin (meaning 'scale'). Fukurin is most noticeable in Hikarimono and was originally thought to occur only in metallic varieties because it was harder to see in other varieties. Fukurin is now seen in large sized Kohaku and Taisho Sanshoku.

(Courtesy of the excellent Book Kokugyo Vol II)