Sometimes dark patches remain visible on the carpet even after a thorough professional carpet cleaning. These dark areas may be from heavy soiling but not necessarily. Most probably the problem is further related to distortion of the pile or fibre. Sometimes clients are dissatisfied with the clean thinking that there is remaining soil when the effect is really from pile distortion.
Carpets deteriorate rapidly in walkway areas. The appearance of the carpet changes due to distortion and wear and tear over time, not simply because of soiling. Distortion may be caused by shading - the change in light reflection as fibres reorient over time, abrading- resulting from the abrasive action of particles rubbing against the fibres and resulting in becoming dull and different absorption of light in less trafficked areas, fading – gradual colour loss due to sunlight exposure, wear – a loss of fibre density from normal traffic or pile reversal. Pile reversal occurs in carpets of all fabric types, all construction types, and all methods of installation. The visibility of shading, including pile reversal, is minimal if the carpet is a loop pile, if it is busily patterned, of pale colour or the carpet is constructed of a less lustrous fibre.
Pile distortion may not be the explanation for every single dark area of the carpet, but it is definitely something to be taken into account. Well-informed and well-equipped carpet cleaners are a key in dealing with carpet fibres issues.