Riddhi Siddhi Trading Co. Offers Optical Brightening Agent with Bluish Tint. Riddhi Siddhi Trading Co. Supplies dyes and textiles auxiliaries. Optical Brightening Agent with Bluish Tint is used for cellulosic fibres, rayon, polyamides, as well as wool and silk. Optical Brightening Agent with Bluish Tint used for various purposes in textile, paper and detergent industries. These optical brighteners are fluorescent white dyes that absorb ultraviolet light and emit back visible blue light. Its model name is Leucophor BCOL p.