What Causes Yellowing and Browning of Carpet and How to Reverse Discoloration
One of the big problems that can happen with carpet is that it sometimes develops a yellow cast.
The most common causes of carpet yellowing are:
1. Use of a detergent with a pH over 10 on stain-resist nylon carpet:
To cure the yellowing from an overly aggressive detergent, rinse with water to remove the excess detergent, apply Brown Out® diluted 1 part Brown Out to 2 parts of water (43 ounces per gallon) to the affected areas, allow to work on the yellowing for 15-20 minutes, do a single wet pass with just plain water and 2 dry passes. Since the stain resistance has been destroyed, apply Bane-Guard™ or Teflon® to the carpet. However, the stain resistance warranty has still been voided! Note that if the yellowing was severe, you may have to apply Brown Out undiluted!
2. Application of silicone protector on stain-resist nylon carpet:
To cure the yellowing from the use of a silicone protector, remove the silicone by normal cleaning followed by the Brown Out treatment at 1:2 with water as above and apply Bane-Guard™. However, in both situations, the warranty has still been voided!
3. BHT yellowing:
BHT (Butylated Hydroxy Toluene) is a common slowly vaporizing preservative used in many plastics including rebound pad. It is even used as a preservative in bread, because it performs well against free radicals. Most of the problems have been on carpets in areas of low air circulation such as in closets, under low-lying furniture, or under throw rugs. Fortunately, the carpet and pad manufacturers no longer use this.
In this photo supplied to us by Beaulieu of America, you can see that the entire carpet has yellowed except where the tackless strip is - and where there there is no pad (cushion) under the carpet. However, this problem can occur out in the middle of the room. Sometimes, most of the carpet will have yellowed except along the baseboard or directly above seaming tape.
This problem seems to occur more frequently in the winter in homes using fossil oil or gas heat. Most carpet manufacturers will not accept this as a claim since it is basically a cushion problem.
To cure this problem, most fiber producers recommend a 10% solution of citric acid to remove BHT yellowing, followed by vacuuming. The primary acid in Brown Out is citric. Using Brown Out at 1 part product to 2 parts water will cure this condition. Simply spray the affected area heavily with this solution, allow at least 15 minutes for the yellow to disappear, and do one single wet pass with water (no detergent) and two dry passes. This removes the excess Brown Out but leaves enough behind to reduce the likelihood of the yellow reappearing. Severe cases may require applying Brown Out undiluted.
4. Mill oil (loom oil / yarn lubricant) on olefin or solution dyed nylon:
Mill oil, also called loom oil or yarn lubricant, is the lubricant used in the tufting machines and sometimes gets onto the carpet face during the tufting process. The yellowing is usually in straight lines. Mill oil residue is most common on solution dyed fibers because the step followed in rinsing out dyes is not needed and so the mill oil isn't removed either. To remove mill oil, simply apply TLS ® 2000 as the prespray and use normal cleaning. If this is a residence or other area where children may crawl around on the carpet, do a Brown Out flush by rinsing the carpet with a 2-4 ounces per gallon solution of Brown Out in water with no detergent through the base unit to remove all alkaline residue. Apply Pro's Choice ARA Anti-Resoiling Agent to reduce resoiling by absorbing any remaining residue.
5. Calcium Chloride Ice melt:
Do a Brown Out flush as above. Use long walk-off floor mats to prevent track-in.
6. Asphalt chemical transfer:
Asphalt coating may be walked onto the carpet (and even onto vinyl tile) from driveways and parking lots and turn the carpet yellow. Since this is being tracked in from the outside, it is most noticeable near the entry areas. This is most common after repaving or sealing the asphalt, especially in the summer with elevated temperatures. Jennite®J-16 driveway sealer causes less problem than other asphalt coatings. This is most commonly a problem on blue and light gray carpet as shown here.
Yellowing from asphalt track-in is virtually impossible to remove. Asphalt coating and sealers are coal tar based materials, which are yellow when highly diluted in solvent. Unfortunately, the solvents required to totally remove these materials are also strong enough to delaminate the carpet. Whenever a customer asks for your advice on replacing carpet and has a parking lot, advise him or her to avoid blue and light gray.
If the problem is fresh, apply TLS 2000 and do your normal cleaning followed with a Brown Out flush at about 2 ounces per gallon. If this fails, prespray Citrus APS™ Spotter, scrub (if loop pile) and clean. Sometimes, adding Energy Prespray Booster to your prespray will help. Use very long floor mats (at least 12 feet) to reduce the problem. The problem, however, will not permanently go away.
7. Optical brighteners:
Optical brighteners are highly specialized dyes which absorb invisible ultraviolet light and re-emit it as visible light, making the carpet appear brighter than it really is. They are used by some carpet cleaning chemical manufacturers who don't realize that their use will permanently cause the carpet to turn yellow. Since these are dyes, there is no cure for this problem. Optical brighteners are frequently found in carpet shampoos and bonnet cleaning compounds. Carpet manufacturers don't approve of carpet cleaning detergents and spotters containing optical brighteners.
8. Direct sunlight and ozone fading, especially on green carpet:
Yellow is typically the strongest dye in carpets. The loss or fading of the other primary colors, red and blue, can leave the carpet with a yellow tint. Yellowing due to direct sunlight fading and ozone fading cannot be reversed except by dyeing.
9. Pesticide treatment:
Discoloration around baseboards and sliding glass doors that have been treated with organophosphate or chlorinated carbamate for insects. This can also be a red discoloration. This condition is irreversible!
10. Soil Abrasion:
Heavy traffic coupled with gritty soil can quickly abrade the carpet giving it a yellowed appearance. This is, of course, irreversible, but can be prevented with proper (12-15 foot) entrance mats and proper maintenance.
Urine must be treated for both stain and odor. The article on Pet Stain Removal has complete details on how to handle urine stains. The You will need Pro's Choice Stain Magic, Pro's Choice Stain Magic for Wool or OS-1 Odor, Stain & Soil Remover.
12. Bleaching Agents:
13. Nicotine (Tobacco):
14. Other causes of yellowing:
Tracked-in oils, cooking oils, burning of candles and floor finishes.
What is carpet and rug browning? Browning is a phenomenon in which, after the carpet or rug is cleaned and has dried, the fiber tips turn dark
Carpet dries from the tips. Therefore, as the cleaning solution evaporates from the tips, the water rises to the surface bringing with it everything dissolved in it, and then the water evaporates leaving everything else behind as illustrated above. This leaves on the tips of the carpet, rug or upholstery soil and high-alkalinity residue plus anything else left in the carpet such as high shampoo levels, cola, coffee, etc. This upward flow of moisture on fiber surfaces during drying is referred to as wicking. The factors contributing to browning are slow drying, over wetting, high alkalinity, BHT, and cellulosic material (jute backing).
In the beginning of this industry, most detergents used were nothing more than glorified concrete floor cleaners, which are highly alkaline and frequently caused browning. Carpets and carpet backings were not as good then either. Equipment now does a better job of leaving the carpet dry. Most carpet-cleaning professionals are now better trained and most (but not all) know better than to over wet a carpet or to use overly strong detergent solutions. Also, the carpet manufacturers now rarely use jute backing.
How to Cure Carpet Browning?
An application of a formulated organic acid agent such as Brown Out® will neutralize this residue not only preventing browning, but actually leaves the carpet cleaner and brighter. Additionally, the use of Brown Out on wet-cleaned upholstery and rugs will reduce the likelihood of dye bleeding by setting the dyes. It is easier to correct browning on carpet with pile yarns made of synthetic fibers than of natural fibers such as wool, hemp, silk or cotton. In cases where severe browning may occur, clean the carpet with Natural Fiber Cleaner.
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