Bluing is an old-fashioned product that was once a staple of the laundry room; chances are good that your grandmother was very familiar with it. Referred to as a whitener, bluing is added to the wash or rinse cycle for the purpose of giving whites a very subtle blue tint. Why blue? Some white fabrics actually have a blue-white hue; bluing makes them appear even brighter, cleaner, and whiter.
Bluing fell out of use as fabric detergents became more effective, but even with the improved formulas, whites gradually begin looking dingy after repeated washings. Chlorine bleach is an effective whitener, but it can weaken fabrics and fibers; bluing is often a better choice. Fortunately, bluing agents can still be found. One brand that Martha likes to use, particularly on antique linens and lace, is called Mrs. Stewart's (no relation).