SOIL FILTRATION LINES
Soil filtration lines are dark soiled areas that develop gradually on carpet. They are most common around the edges of a room next to the wall, under floor length draperies and under doors. But they can develop anywhere there is an air space such as between floorboards or spaces in the sub-flooring.
The soiling is caused by the passage of air through or across the carpet. Air carries microscopic particles of dirt settle and becomes embedded in the carpet pile yarns. In areas where the air flows over the carpet more rapidly than normal, the carpet acts as a filter, extraction the soil particles from the air. The soil is very fine and can penetrate deeply into the yarns. Special techniques by a professional carpet cleaner are usually required to improve the appearance of soil filtration lines.