sorry, a bit off topic, but I just read this when reading about washing wool sweaters..
Fulling or tucking or walking ("waulking" in Scotland) is a step in woollen clothmaking which involves the cleansing of cloth (particularly wool) to eliminate oils, dirt, and other impurities, and making it thicker.
In Roman times, fulling was conducted by slaves standing ankle deep in tubs of human urine and cloth. Urine was so important to the fulling business that urine was taxed. Urine, known as 'wash', was a source of ammonium salts and assisted in cleansing the cloth.