Occasionally, a brownish discolouration appears on a carpet or rug after it has been cleaned. One of the causes of this discolouration is a condition called cellulosic browning. For this discolouration to develop, several factors must be present: a cellulosic fibre, moisture, and slow drying. A high pH or shampoo residue may also contribute to the occurrence.
Cellulosic fibres are present in all jute carpet or rug backings and are a major source of cellulosic browning. The drying time following carpet cleaning depends on humidity; during rainy periods and summer months, the air contains more moisture, making it more difficult for the moisture in the carpet to evaporate.
The age of the carpet is also important. Jute backings deteriorate over time and undergo chemical changes. These changes produce brown or red colourants (lignin) which can wick up to the face yarns and appear on the surface of the carpet after cleaning. As the carpet dries, the brown or red colour remains on the tips of the tufts.
Cellulosic browning of a similar type occurs when newspapers are left outdoors or gradually age indoors. The cellulosic materials in the paper turn brown and become brittle.
If browning does develop after cleaning, professional carpet cleaners can often remove the discolouration, as it is not always a permanent stain. In other cases, however, the discolouration cannot be completely removed. This arises more often with wool, sisal, or cotton carpets, or when the carpet is old enough for advanced cellulosic fibre degradation to occur.
