Occasionally after a carpet or rug has been cleaned, a brownish discoloration appears. A condition called cellulosic browning is one of the causes of this discoloration. Several factors must be present in order for this discoloration to develop including a cellulosic fiber, moisture, and slow drying. Furthermore, a high pH or shampoo residue may also contribute to its occurrence.
Cellulosic fibers are a major source of cellulosic browning and are present in all jute carpet or rug backings. The drying time following carpet cleaning depends on humidity; the air contains more moisture during rainy periods and summer months, making it more difficult for the moisture in the carpet to evaporate.
The age of the carpet is also important, as jute backings deteriorate over 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. The brown or red color remains on the tips of the tufts as the carpet dries.
A similar type of cellulosic browning 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 is not always a permanent stain and can often be removed by professional carpet cleaners. However, in other cases, the discoloration cannot be completely removed. This issue arises more often with wool, sisal or cotton carpets, or when the carpet is old enough for advanced cellulosic fiber degradation to occur.