Bluing

Blue coloring materials that are added to wash or rinse water and are taken up by fabrics; bluing counteracts the yellowing that sometimes develops in white fabrics after repeated use and laundering.  Bluing produces a blue-white hue on fabrics, which is considered more pleasing to the eye than yellow-white.  As a separate laundry additive, bluing may be a blue dye or pigment. It is available in liquid or dry form for adding to the rinse, in a granular detergent base for adding to wash water along with soap or detergent, and as an ingredient in other laundry products, including detergent oxygen bleach, fabric softener, and starch.