Yellowing occasionally appears after professional cleaning of light colored carpeting, rugs, upholstery, draperies or other textile furnishings. This discoloration occurs for a variety of reasons, and it is usually indicative of another preexisting problem. The yellowing is generally not noticeable until after the item is cleaned, either because the dirt is 'hiding' it or some latent problem is catalyzed by customary cleaning. This is not the fault of the cleaning process. The customer is often disappointed that the interior furnishing is clean but did not return to its new condition. Occasionally, the yellowing will be in one area but not in another, such as under furniture, or in front of a window where some other condition has initiated the yellowing, only to be exposed by the cleaning method.
One Common Reason for Yellowing: Photo-Oxidation
Some fibers are prone to photo-oxidation due to normal exposure and use. With ordinary light, sunlight and atmospheric fumes, certain white fibers, especially when bleached or optically brightened, will eventually begin to yellow. Customary wet cleaning is sometimes enough to induce a yellow coloration in white or off-white colored wool that was previously damaged by light and atmospheric conditions.
Stain-Resistant Chemistries and Early Generation Nylon
On some stain-resistant finishes, silicone-based soil retardant finishes and early generation nylon, the manufacturing chemistries tend to yellow with age, exposure to UV light and/or cleaning with a high pH cleaner.
Many textile finishes also yellow with age. These finishes can include: flameproofing, crease resistance, insecticides, anti-static and textile lubricants or softeners. All are used on textile furnishings.
Fluorescent Brightening Agents
Some fluorescent brightening agents (FBA) can yellow with age and exposure to UV light. These brighteners are found in many detergents and spot removers. FBAs are also used on some white colored textiles.
Anti-oxidants, such as BHT and formaldehyde, are found in carpet cushioning, some latex preparations, upholstery foam, in carpet backings and many other common construction materials. The anti-oxidants redeposit or wick up to the carpet face yarns or fabric surface and yellow on contact with oxygen.
Light colors such as beige or tan are often composed of several dyes. Some of these dyestuffs can fade, altering the hue towards yellow.
Long forgotten spills, stains and pet accidents also can yellow with age. Sugary drink stains and animal urine are examples.
Common soil and dirt from normal use can be yellow in coloration. Abrasive action on carpet fibers from normal soiling can also cause permanent discoloration.
There are many possibilities for yellowing. A yellow discoloration is more apparent when it occurs on a white or off-white background. A professional cleaner has several different techniques available that may reduce the effect of yellowing caused by many of these preexisting conditions. These include treatment with special yellow remover products, bleaches and adjusting the fiber's pH to improve its appearance. Using professional chemicals, yellowing can be removed in some cases; in other cases, it can be lightened somewhat, but in many situations the yellow discoloration is permanent.