The Dyeing of Cotton Fabrics: A Practical Handbook for the Dyer and Student — John Shaqi
The Dyeing of Cotton Fabrics: A Practical Handbook for the Dyer and StudentBeech, Franklin
Science
The Dyeing of Cotton Fabrics: A Practical Handbook for the Dyer and Student
Beech, Franklin
Dyes and dyeing -- Cotton
(9) =Chemicing.=--This is the actual bleaching operation, familiarly
known as "chemicing," that is, the treatment of the goods with bleaching
powder. The previous operations have resulted in obtaining a cloth free
from grease, natural or acquired, and from other impurities, but it
still has a slight brownish colour. This has to be removed before the
goods can be considered a good white, which it is the aim of every
bleacher they should be.
To get rid of this colour they are subjected to some final operations,
the first of which is now to be considered. The chemicing consists in
running the goods through a weak solution of bleaching powder (chloride
of lime), piling the goods up into heaps, and allowing them to lie
overnight, the next day they are finished. As the cloth has received, or
ought to have received, a thorough bottoming, only a weak bath of chemic
is required, about 1/2 to 1 deg. Tw. is quite sufficient. The solution is
prepared in a stone cistern. There is very little difficulty in making
it, the only precaution necessary is to have the solution quite clear
and free from undissolved particles, for if these get upon the cloth
they will either lead to the production of minute holes, or they may
overbleach the fibre, which in such case will have the power of
attracting excess of colour in any subsequent dyeing process and thus
lead to stains, the origin of which may not be readily grasped at the
first sight.
It is best, therefore, either to allow the solution to settle in the
cistern till quite clear, which is the simplest way, or to filter
through cloth.
The chemicing is best done cold and with weak solution, at 1/2 deg. Tw.
rather than 1 deg. Tw. Warming the liquor increases the rapidity of the
bleaching action, but there is a risk of over-chloring, which must be
avoided as far as possible, because there is then danger of tendering
the fibre, moreover, such over-chlored cloth has an affinity for
colouring matters that is not at all desirable, as it leads to the
production of stains and patches in the dyeing operations. It is much
better, when a single chemicing does not bleach the cloth sufficiently
and give a white, to run the cloth twice through a weak liquor rather
than once through a strong liquor.
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