Preventing those black lines along the edges of your carpeting ....... They are called soil filtration and will usually appear if you live in a major city like Boston or if you live in the suburbs and have a garage under or even sometimes an oil-fired heating system. It's soot that is drawn into the interior wall cavities of your home due to negative air pressure and exits out of the wall cavities where the wall meets the floor, depositing the soot in the carpet fibers which are acting as a filt...