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DYEING AND CALICO PRINTING.

B. The colouring matter combines with the fibre ; the colour is the result of

this union.

This simple dyeing maybe subdivided into:—

a. The woven fabric or fibre is immersed in a bath or solution ofcolouring matter at the ordinary, or at a higher, temperature. Thefabric gradually draws the colouring matter from the bath by atrue chemical attraction. In this manner a uniform colour isimparted to the whole tissue, unless a resist had previously beenprinted on ; or, the uniform colour is subsequently discharged incertain patterns by means of acids and other reagents. Examples:The dyeing of woollen and silken fabrics with aniline colours,sulphindigotic acid, picric acid, orceine. Vegetable fibre cannotbe dyed by this method.

(3. The colouring matter is printed on the cloth after mixture with athickener , and the colour is subsequently developed by exposureto the heat of steam.

C. The colouring matter becomes incorporated , but not chemically combined ,

with the fibre.

I. The fixation of colour by surface attraction at the moment of

separation from the solvent, as with carthamine; or precipitationdue to the aCtion of porosity and surface attraction upon a colourwhich is only feebly united to a solvent, as with indigo, annatto, &c.*

II. Fixing colouring matter properly dissolved by means of the chemicalattraction exerted by a previously mordanted fibre. The differencebetween this method and that described under B is, that in con-sequence of the absence of any affinity between the colouring matterand the fibre, the latter has been prepared or provided with aninsoluble substance, which possesses the power of combining withthe colouring matter, and of fixing it firmly to the fibre. Mordantsdo not aCt in this manner only, but exercise as well the function ofvarying and regulating the shade and the depth of colour. Forexample, when non-mordanted wool is steeped in a solution ofcochineal, it will assume a claret-red or a grenadine-red colour;but if the wool has previously been mordanted, it will assume abright scarlet. Cotton fabrics previously mordanted with iron oralumina mordants will, on immersion in a madder bath, exhibit aviolet, black, red, pink, or chocolate colour, according to the nature ofthe mordant and its strength.

III. Fixing by oxidation. The colouring matter, or rather the mattercapable of development as a colour, is applied to the fibre in solution(either by immersion or by printing), and is next submitted to anoxidation which precipitates or fixes and as well developes the colours.Examples: the fixing of catechu, logwood, aniline black. The oxi-dation is induced—

a. By exposure to air, with or without addition of any alkaline substance.

* The development of the colour requires, in the first instance, a subsequent oxidation,which does not, however, render the colour more durable, nor prevent re-solution in anymenstruum similar to that of the first solvent.