DYEING AND CALICO - PRINTING (Fn., Teinture, Impression; Gee., Farberei, Zeugdruckerei).
These terms are used to signify the arts of producing at will colours upon textile fabrics, whether of animal or of vegetable origin. " Dyeing," in the strict sense of the word, is confined to those operations by which loose fibre, yarns, or woven goods, are made to assume some uniform colour. "Calico-printing," or, as it may be more properly called, "tissue-printing," is the produo tion upon yarns or cloth of designs of two or more colours. Patterns in different colours may, how ever, be obtained by simple dyeing, in the case of tissues composed of more than one kind of fibre, such as wool and cotton, or silk and cotton. In virtue of certain specific properties, to which reference will be made below, animal and vegetable fibres take up colours in a very different manner, so that if a design be produced in such mixed fabrics by the art of the weaver, it will, if skilfully dyed, exhibit such a design in different colours.
The arts in question are based on the power of organio fibres to absorb colouring matters, and to retain them with a greater or less degree of persistence. This absorption is now considered to be mainly physical, rather than chemical, in its nature, and to depend on the presence, in each fibre, of innumerable pores, too small to be recognized even by the microscope, into which the colour penetrates, and where it is held by means of surface attraction. Chemical affinity plays, however, an undeniable part. Thus, if we place in a solution of magenta, or of piorio acid, a piece of mixed oloth, say of wool and cotton, the woollen threads will be fully and permanently coloured, whilst the cotton threads will either remain entirely white, or at moat exhibit a alight stain, which is easily removed by rinsing in cold water. The affinity or colouring matters for animal fibres—wool, silk, &c., is, with very few exceptions, mnch stronger than for vegetable fibres—cotton, linen, jute, hemp. Hence yarns and oloths of vegetable matter are decidedly more difficult to dye.
It has been long ago observed that certain colours combine with textile fibres very readily on mere contact. Thus the majority of the aniline colours are at once absorbed by wool and silk, and carthamine, the red colouring prinoiple of safflower, is quite as readily taken up by cotton. Such colours are known as "substantive colours." The majority of colouring matters, however, do not thus combine with the fibre, but require the intervention of a " mordant," i. e. a body which possesses an attraction, physical or chemical, both for the fibre and for the colour, and thus enables the two to unite.
The selection and use of these mordants is, therefore, a most essential part, both of the theory and the practice of dyeing. For the most part, they consist of metallic salts, such as the sulphate, nitrate, and acetate of alumina, and its double sulphate, commonly known as alum ; the proto- and per-chlorides of tin (stannous and stannic chlorides); the so-called nitrate of tin ; the sulphates, nitrates, and acetates of iron, and their mixtures ; the sulphate of copper (blue stone or blue vitriol), and the acetate of copper (verdigris); the nitrate and acetate of lead ; the chloride and tartrate of antimony. There are also compounds extensively used as mordants, in which a metallic oxide playa the part of an acid, in combination with soda or potash. Such are the stannate, aluminate, and plumbate of soda ; and, above all, the ohromates of potash.
The bitartrate of potash, commonly known as tartar or ergo], likewise plays on important part in mordanting woollen goods, though its action is by no means perfectly understood. The above mentioned bodies, if mixed, in a state of solution, with e.g. the decoction of a dye-wood, precipitate the colouring matter more or less completely, leaving the liquid clear. These precipitates are called "lakes," and are supposed to be produced in the pores of the fibre, if the latter be saturated first with the mordant, and then immersed iu a solution of a dye.