Fulling involves two processes, scouring and milling (thickening). Originally, fulling was carried out by pounding the woollen cloth with the fuller's feet, or hands, or a club. In
Scottish Gaelic tradition, this process was accompanied by
waulking songs, which women sang to set the pace. From the medieval period, however, fulling was often carried out in a
water mill, followed by stretching the cloth on great frames known as tenters, to which it is attached by
tenterhooks. It is from this process that the phrase being on tenterhooks is derived, as meaning to be held in suspense. The area where the tenters were erected was known as a
In Roman times, fulling was conducted by slaves working the cloth while ankle deep in tubs of human
urine. Urine was so important to the fulling business that it was
taxed. Stale urine, known as wash, was a source of
ammonium salts and assisted in cleansing and whitening the cloth. By the medieval period,
fuller's earth had been introduced for use in the process. This is a soft clay-like material occurring naturally as an impure
aluminium silicate. It was used in conjunction with wash. More recently, soap has been used.
The second function of fulling was to thicken cloth by matting the fibres together to give it strength and increase waterproofing (
felting). This was vital in the case of
woollens, made from
wool, but not for
worsted materials made from combing wool. After this stage, water was used to rinse out the foul-smelling liquor used during cleansing. Felting of wool occurs upon hammering or other mechanical agitation because the microscopic barbs on the surface of wool fibres hook together, somewhat like Velcro.