Color Index, C.I.

Color Index, C.I. international name classification of color agents introduced in 1925; the name is composed of “C.I.”, “Class” (dyes, pigments), “Color name” (chromatic color from the color circle or a tertiary tone, achromatic color, metallic), “Type number” (consecutive index number for the various chemical substance and application types, e.g. acid/alkaline substances, diazo dyes, color couplers, food colors, optical brighteners, bleaching agents), “Constitution number” (consecutive chemical modification number), e.g. C.I. Pigment Blue 15:1.