What Is It about Bleach That Makes Colors Less Colorful?
Bleach is used industrially and domestically to whiten clothes, lighten hair color and remove stains. Bleach has broad spectrum bactericidal properties, making it useful for disinfecting and sterilizing and is used in swimming pool sanitation to control bacteria, viruses, and algae and in many places where sterile conditions are required. It is also used in many industrial processes, notably in the bleaching of wood pulp. Bleach is also used for removing mildew, killing weeds, and increasing the longevity of cut flowers.
Although we use the term bleach as if it was only one substance, there are actually several different types of bleach. The most popular is common household chlorine bleach, which is a water-based product that contains a chemical called sodium hypochlorite. Another popular type of bleach is oxygen bleach, which contains hydrogen peroxide or other compounds that release peroxide when mixed with water. Bleach also comes as a powder in the form of a chemical called calcium hypochlorite.
All of these bleaches can be used to whiten clothing. They also make good cleaning agents, since they kill mold, germs, and bacteria. A solution of bleach and water is often used to clean and disinfect hard surfaces in kitchens and bathrooms, for example. Even though early man didn’t understand the science behind bleach, the bleaching process has been around for thousands of years.
To understand how bleach removes color, it is helpful to understand a bit about how colors work. Chemical compounds — called chromophores — cause colors by reflecting a certain portion of the visible spectrum of light. For example, a blue dress contains chromophores that reflect blue light that our eyes see as the color blue.
Bleach works by releasing oxygen molecules in a process called oxidation. The oxygen molecules released by bleach break up the chemical bonds of chromophores. The changed chromophore molecules either reflect no color or a color outside the visible spectrum. This absence of color is seen by our eyes as white.
You may have also noticed that fabrics left out in the sun will look faded or bleached over time. Does sunlight have bleach in it? Nope! But sunlight can work like bleach. High energy ultraviolet sunlight can disrupt the chemical bonds in chromophores, causing them to lose their color much like the oxidation process with bleach.