In the discharge method of
printing, fabric is often dyed in the piece and then printed with a chemical that will
destroy the colour in designed areas. Sometimes the base colour is removed and another
colour printed in its place, but usually a white area is desirable to brighten the overall
design. The usual method of producing discharge prints is to print the design, such as
polka dots, with a paste containing caustic soda and sodium hydrosulfite. A steaming
follows and then there is a good washing to remove the by-products of the reaction.
The mordant process is called the discharge process. Here the cloth is prepared with
various mordants so that when it is immersed in a dye bath, the reaction produces
different colours on the cloth. Only those portions which have been prepared take the dye.
Various deep shades of great brilliance are produced by the variable use of mordant.
Alizerine is the colouring substance of mordant. In the current discharge process, cloth
is dyed in the desired background colour from those portions where chemicals have been
applied. The discharge parts of the design are then further processed. Depending on the
class of the dye and the style of printing employed, the printed and dried cloth is
steamed.
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