Dyes are chemical compounds that are added to fibres to give them colour. Sometimes these dyes react with chemicals or gases and changes in the colour occur. Fume fading is a reaction to gaseous pollutants, such as oxides of nitrogen or sulphur, in the air. It is a gradual change, accelerated by sunlight, heat, high humidity and the presence of acid on the fibre. The most common colour changes are blues to pink, greens to yellow, and browns to red. The colour changes usually start at the tips of the tufts and progress toward the backing.
Ozone fading is caused by ozone gas in the atmosphere. It is also accelerated by high humidity and heat. Ozone is more prevalent around electrical motors, fluorescent lights, and during lightning storms. It is also formed by the reaction between light and pollutants in the air. Fibres subjected to ozone fading may lighten, turn white, or change from one colour to another as in fume fading.
Some carpet fibres are dyed with Indicator Dyes. These dyes are sensitive to either acid or alkaline chemicals. An alkaline-sensitive dye will change colour if exposed to ammonia or high alkaline (high pH) detergent. The colour often can be changed back with dilute acetic acid (white vinegar). An acid-sensitive dye will change colour when exposed to vinegar or other mild acids (low pH) used in cleaning. The original colour often can be restored with dilute ammonia. These colour changes may not be permanent and often can be reversed.
Other colour changes due to strong chemicals (concentrated acids and bases or other reactive chemicals) are not a result of this “indicator effect” and may not be reversible. Colour changes that become apparent after cleaning are sometimes incorrectly blamed on the cleaner or cleaning process. In many cases, however, the colour change is due to the ravages of time—the aging of dyes and fibres. Cleaning reveals the true colour by removing dirt and loosened dyes.
