After the pieces have been milled down to the desired degree, they
present an uneven and, undesirable appearance on the surface, the ends
of many of the fibres which previously projected having been turned and
thus become embedded in the body of the cloth. In order to bring these
hairs to the surface again, the fabric is subjected to _teasing_ or
_raising_, an operation identical in principle with one which has
already been noticed under the finishing of cotton. In place of the
steel wire brushes it is the usual practice to employ teasels for the
treatment of woollen goods.
The teasel (see Fig. 7) is the dried head (fruit) of a kind of thistle
(_Dipsacus fullorum_), the horny sharp spikes of which turn downwards
at their extremity, and, while possessing the necessary sharpness and
strength for raising the fibres, are not sufficiently rigid to cause
any material damage to the cloth. For raising, the teasels are fixed
in rows on a large revolving drum, and the piece to be treated is
drawn lengthways underneath the drum, being guided by rollers or rods
so as to just touch the teasels as they sweep past. In the raising of
woollen goods it is necessary that the pieces should be damp or moist
while undergoing this treatment.
After teasing, the pieces are stretched and dried. At this stage they
still have an irregular appearance, for although the raising has brought
all the loose ends of the fibres to the surface, these vary considerably
in length and thus give rise to an uneven nap.
[Illustration: From Ganswindt, _Technologie der Appretur_.