Dyes are chemical compounds that are added to fibers to give them color. Sometimes, changes in the color occur when these dyes react with chemicals or gases.
Fume fading is a reaction to gaseous pollutants, such as oxides of nitrogen or sulfur, in the air. It is a gradual change, accelerated by sunlight, heat, high humidity and the presence of acid on the fiber. The most common color changed are greens to yellow, blues to pink, and browns to red. The color change usually starts at the tips of the tufts and progresses toward the backing.
Ozone fading is caused by ozone gas in the atmosphere, and is also accelerated by high humidity and heat. Ozone is more prevalent around fluorescent lights, electrical motors, and during lightning storms. It is also formed by a reaction between light and pollutants in the air. Fibers subjected to ozone fading may lighten, turn white, or change from one color to another as in fume fading.
Some carpet fibers are dyed with Indicator Dyes, which are sensitive to either acid or alkaline chemicals. An alkaline-sensitive dye will change color if exposed to ammonia or high alkaline (high pH) detergent. Using dilute acetic acid (white vinegar), the color can often be changed back. An acid-sensitive dye will change color when exposed to vinegar or other mild acids (low pH) used in cleaning. Using dilute ammonia, the original color can often be restored. These color changes can often be reversed and may not be permanent. Other color changes which are not a result of this “indicator effect” may not be reversible, including those due to strong chemicals (concentrated acids and bases or other reactive chemicals).