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DYEING AND CALICO PRINTING.

complicate the dyeing operations, and to diminish the beauty of the colours.These colouring substances do not admit of being directly fixed on textilefibres, the intervention of a mordant being an absolute necessity. Most ofthese mordants are metallic oxides, those chiefly used being the hydratedoxides of aluminium, peroxide of iron, and the sesquioxide of chromium..These oxides are incorporated with the fibre of the tissues by being broughtinto contact therewith as soluble salts, when they are precipitated and fixedin the fibre. The mordanted tissue, on being placed in a dye-beck containingthe dye stuff, attracts the colouring matter, and combines with it in preciselythe same manner as if the tissue were not present,—that is to say, that theaffinities are only exercised between the colouring matter and the metallicoxide, while the tissue serves no other purpose than that of a framework inwhich both are mechanically held. There is thus formed a coloured lakeadhering to the cloth, and the shade of colour, as well as its kind, varies withthe nature of the oxide applied. This is red, rose, or pink coloured, whenalumina is used; black, violet, or lilac, with iron, and chocolate, when amixture of both these is made use of. Hence it follows that a dye-beckcontaining one and the self-same dye stuff (say madder) will produce, uponvariously mordanted fabrics, very varying colours. In some cases a thirdsubstance is employed along with the madder pigments and the mordant, viz.,a peculiarly modified fatty substance, as is the case in Turkey red dyeing,where this body gives greater stability and brilliancy of colour to the compoundproduced by the mordant and pigment. Generally the mordants are firstapplied to the tissue. This may, of course, be done in such a manner as toform designs and patterns by the aid of engraved rollers; after which thewhole fabric is immersed in a dye-beck containing the madder, garancin, orfleur de garance, as the case may be, and treated as if it were to be uniformlydyed.

Madder colours are rarely printed diredtly on the fabrics. The use of madderand of fleur de garance implies some other operations after the textile fabricsleave the dye-beck, the aim of which operations is partly the bleaching orwhitening up of those portions of the tissue which are intended to be leftwhite, since it is not possible so to manage the dyeing process as not to soil,more or less, the portions of the fabric where no mordant at all is applied.On the other hand, the coloured portions have to be rendered bright andbrilliant by soaping and clearing, whereby the colours are freed from suchmaterials as would injure their beauty, viz., the yellowish substances presentin the dye materials applied. When garancin, pincoffin, or any of the extradlsof madder are used, the process of soaping and clearing ( avivage ) is notneeded to the same extent, and a slight treatment with chlorine is quitesufficient to restore the purity of the white portions of the tissues. It shouldbe observed that the colours are then less brilliant, less full-bodied and deep,than when madder is used and clearing employed. It depends, of course, uponthe choice of the manufacturer, and upon the peculiar destination of the goods,whether madder, garancin,. or fleur de garance is selected. When garancin orcommercial alizarin is used, catechu can be applied simultaneously if desired,but this cannot be done with madder or fleur de garance, which requireavivage.

The ordinary madder dyeing operation for the production of red (exclusive