Housewives who wish to do successful home dyeing should therefore not
purchase dyes indiscriminately, but should select the kind best suited
to the material, because the coloring principle which will remake a
silk waist may utterly ruin a woolen skirt or a linen suit. Powders
designed for special purposes may be purchased from druggists.
228. Indirect Dyeing. We have seen that it is practically impossible
to color cotton and linen in a simple manner with any degree of
permanency, because of the lack of chemical action between vegetable
fibers and coloring matter. But the varied uses to which dyed articles
are put make fastness of color absolutely necessary. A shirt, for
example, must not be discolored by perspiration, nor a waist faded by
washing, nor a carpet dulled by sweeping with a dampened broom. In
order to insure permanency of dyes, an indirect method was originated
which consisted of adding to the fibers a chemical capable of acting
upon the dye and forming with it a colored compound insoluble in
water, and hence "safe." For example, cotton material dyed directly in
logwood solution has almost no value, but if it is soaked in a
solution of oxalic acid and alum until it becomes saturated with the
chemicals, and is then transferred to a logwood bath, the color
acquired is fast and beautiful.
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