Saturday, February 12, 2011

EVALUATION AND ANALYSIS OF DYE STUFFS

FROM
            The present standpoint dye stuffs fall into the following groups.

Basic Dye stuffs
                
            These are organic bases of certain types containing free amino groups . They form salts with acids such as hydrochloric or oxalic acids , and double salts with certain metals such as zinc. For dyeing they are supplied in one or other of the above forms either pure or diluted with an inert body such as Dexedrine . For the coloring of
oils they are supplied as the free base . They dye silk ,wool,jute,and nylon from neutral ,slightly acid or soap containing baths .
            They do not dye cotton itself but as they form insoluble compounds with tannins and tannins are absorbed strongly by cotton with tannin .To obtain improved results the tannin may before dyeing be converted on the fibre into the insoluble antimony salt. They also form precipitates with many acid and direct cotton dyes and can therefore not be used in the same bath with such colors.  As a class they give very bright shades but that is almost their only virtue and they are rapidly dropping out of use.

True Mordant Dye stuffs
        
              These dye stuffs do not dye wool at all well alone but combine with chromium aluminium and iron to form lakes .The will therefore dye wool which has previously been treated with a salt of one of these metals.
They are often exceptionally fast but usually dull in shade . As their affinity is for the metallic mordant and not for the fibre they will dye any fibre wool cotton silk viscose which can be induced to become mordanted with a suitable metallic salt.