When does browning occur?
Browning can only occur if three factors are present: 1. A cellulosic fibre, 2. Moisture, and 3. Slow drying. If the water used to clean the carpet comes into contact with cellulosic fibres (eg. in the jute backing) then a small portion of cellulosic material may dissolve and be carried up the tufts by a wicking process as the carpet dries. As the last of the water evaporates, the tips of the tufts may become badly discoloured with brown stains. The slower the drying, the more browning that will occur. This is because the moisture evaporates from the tips of the tufts and the brown discolouration is carried right to the top of the carpet. Over-wetting a carpet increases the risk of browning. On the other hand, if the carpet is dried quickly, then the tips of the tufts dry out first and browning is prevented from rising or wicking out.
How do you recognise browning?
Spread the pile apart and observe the location of the brown colour. If it is browning, it will be located on the highest part of the carpet: the tips of the tufts on a cut-pile carpet or on the sides of the fibres if the pile has been flattened by traffic (still the highest part of the carpet). Browning may appear as random circles of yellow-brown patches evenly distributed over the carpet. Soil will tend to hide browning. Browning has a tendency to darken in colour with time as it oxidises and develops.