Shading: A Cleaning-Related Challenge

Shading is one of the most common complaints the professional cleaner or inspector encounters. It appears in both commercial and residential environments, and is not a phenomenon that is easily explained to the customer; for some reason, they just don’t get it. That’s why it’s so important for the professional cleaner to understand and explain shading prior to cleaning.

Shading is a change or variation in light reflection as pile fibers are bent or abraded. Common terms associated with shading are pooling, watermarking, pile reversal, crushing, and erroneously as premature wear. It is most commonly seen in single-color (plain) carpet and carpet with small patterns, but it may be encountered in almost any carpet construction or style.

While most shading becomes noticeable when carpet is fairly new, shading may not become an issue with customers until carpet is carefully evaluated after cleaning and grooming, in which case it is quite likely that the cleaner will be blamed, if only because the cleaner is the last one who touched the carpet.

So what causes circular, oval or overall patterns of distortion in carpet, particularly cut-pile styles? What can be done about it, and how do cleaners explain this phenomenon to customers? There are several causes but, absent physical pile damage, shading is related primarily to four sources:
  1. Fiber characteristics
  2. Wear
  3. Abrasive soiling
  4. Subfloor imperfections

So, what is shading?

Shading is a variation in light reflection from fibers or pile yarns that are bent or abraded. Mind you, this isn’t a difference in color or hue, but merely an apparent change in color as light is reflected in different ways from fibers of the same color.

Confirmation of shading can be made by standing at one end of a distorted area and observing the light-dark contrast. In areas where the pile yarns are lying away from the point of viewing, the pile will appear lighter because more light is reflected from those yarns. In areas where the pile yarns are lying toward the viewer, the area will appear darker, because the viewer is seeing shadows between yarn ends or tufts. When viewed from the opposite end of the shaded area, the light-dark contrast reverses itself.


Wear is defined by carpet manufacturers as a 10 percent reduction (thinning out) in pile fiber density, which rarely happens. It’s different from the consumer’s perception of wear, which most likely includes any texture change, resiliency or soiling problem. But eventually, fibers will thin out in traffic areas, causing a slight change in appearance of any carpet over time. That’s normal and it doesn’t meet the manufacturer’s definition of wear.

As mentioned above, there are four primary causes for carpet shading. Looking at fiber characteristics, there are several possibilities:
  1. Lack of resiliency (crushing) - Certain fibers are resilient; that is, they spring back when crushed by traffic. Others are not resilient. Nylon is the most resilient of the synthetic fibers, while olefin (found mainly in Berber styles) and acrylic are not. Many consumers purchase an inexpensive olefin Berber only to see traffic lanes flatten out in a few months due to traffic on this non-resilient fiber. The same is true of acrylic, but there is very little acrylic being used in carpet today. Typically, pile reversal or crushing are terms associated with olefin and acrylic pile fiber, but remember, any fiber can crush under weight (e.g. 500-pound sofa).
  2. Crimp loss – Polyester fiber is made from recycled pop bottles. It is spot- and stain-resistant and cleans well. However, over time, traffic and maintenance tends to elongate the fiber, causing it to lose its crimp. This causes a texture change in traffic areas, compared to areas along walls and under furniture.
  3. Pooling – Originally, pooling was associated with round or oval distortion patterns in wool carpet. Pooling is a wool fiber characteristic, not a defect. It gives every wool carpet unique “personality.” Often wool is combined with nylon (80 percent wool, 20 percent nylon) to minimize the appearance of pooling.

With abrasive soil, particle soils can scratch and abrade synthetic fibers causing variation in light reflection. This is like rubbing a clear sheet of plastic with sand paper. Clean the plastic all you want, but it remains dull and dingy looking in traffic areas compared to un-trafficked areas along walls or under furniture. Since wool has a somewhat dull epidermis due to its overlapping scales, soil shading is not a problem.

Regarding subfloor irregularities, even when concrete flooring is poured to building code specifications, it isn’t perfectly level. Eventually, these irregularities “telegraph” to the surface of carpet pile causing variable light reflection in large areas. This typically is referred to as water marking or even pooling. It normally shows up primarily in commercial (contract) carpet installations.

Roll crush is pretty much like it sounds. Crush marks develop when fabrics are rolled while fibers are hot or, most likely, when subjected to excessive weight or heat during shipping or storage. They appear as bands of flattened pile usually running across the width of rolled, pile fabrics, such as velvet upholstery, or cut or loop-pile carpet. Generally, roll crush marks or bands become lighter, narrower and closer together as they progress toward the center of the roll.

Bottom line, if you know what the pile fiber of the carpet, you can get an idea of what is causing the shading. Rest assured, however, that any fiber used as a floor covering will display some form of shading over time.

Correcting Shading

Wool carpet and rugs are subject to a form of shading that originally was called “pooling.” This variation in light reflection is caused by traffic in entry and pivot areas, and which is routed around furniture as well. Variation in light reflection is caused when wool fiber in these areas splays out due to pivoting or turning traffic. Of course, more wear (i.e., thinning of pile density) is experienced in these heavy-use areas as well.

Shading may be corrected by careful cleaning, using hot-water extraction, followed by grooming the pile uniformly in one direction. The problem is, when traffic is re-introduced, the shading will most likely return.

This condition should be anticipated by professional cleaners and explained to customers in advance. Again, this is not a defect, but rather a characteristic of carpet. It makes each carpet installation unique and impossible for the professional cleaner to anticipate.

Watermarking is a much larger pattern of shading. It makes carpet appear to have different color hues; however, this is not the case. Even if the carpet is removed and replaced with carpet of similar style, shading of the same watermarked patterns will return. This is why subfloor irregularities telegraphing through the carpet is considered a possible cause.

If you fail to convince your client and argument develops, you can suggest getting a second opinion from an industry expert to confirm your explanation. An IICRC-Certified Senior Carpet Inspector (SCI) may be of assistance.

Occasionally, a cleaning technician may be called on by a carpet manufacturer to try to correct a particularly bad example of pile reversal in a large, prestige installation where replacement cost would be high. Unfortunately, attempts to correct the problem completely are seldom successful. Hot-water rinsing followed by careful grooming is the most common method for attempting correction, but even then, once traffic is re-introduced, the shading returns.

Roll crush is usually successfully corrected by either hot-water extraction or steaming followed by immediate grooming with the pile lay.

Most carpet manufacturers and cleaners alike agree that the shading phenomenon cannot be considered a fault, but rather a characteristic of carpet. Manufacturers tend to judge each case on its merits and prefer not to get involved in litigation.

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