Occasionally a brownish discoloration appears on a carpet or rug after it has been cleaned. One of the causes of this discoloration is a condition called cellulosic browning. In order for this discoloration to develop, several factors must be present: a cellulosic fiber, moisture and slow drying. A high pH or shampoo residue may also contribute to its occurrence.
Cellulosic fibers 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 in time and undergo chemical changes. These changes produce brown or red colorants (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 color remains on the tips of the tufts.
Cellulosic browning of a similar type occurs when newspapers are left outdoors, or gradually age indoors. Cellulosic materials in the paper turn brown and become brittle.
If browning does develop after cleaning, the discoloration can often be removed by professional carpet cleaners as it is not always a permanent stain. In other cases, however, the discoloration cannot be completely removed. This arises more often with wool, sisal or cotton carpets, or when the carpet is old enough for advanced cellulosic fiber degradation to occur.