614 



CALICO-PRINTING 



the latter is preferred, because it communicates more transparency to the dyes, and 

 because, in spite of the washing, more or less of the starch always sticks to the 

 mordant. Gum has the inconvenience, however, of drying too speedily, and forming 

 a hard crust on tho cloth, which does not easily allow the necessary capillary attrac- 

 tion to take place, and the tints obtained arc thin and meagre. The substances gene- 

 rally employed in thickening are : 



1. Wheat flour. 



2. Wheat starch. 



3. Torrefied wheat starch, or British 



gum. 



4. Torrefied potato farina. 



5. Gum substitutes or soluble gums. 



6. Gum Senegal. 



7. Gum tragacanth. 



8. Salop. 



9. Pipe-clay or china-clay mixed 

 with gum Senegal. 



10. Sulphate of lead. 



11. Molasses. 



12. Dextrin. 



13. Albumen of eggs. 



14. Lactarino. 



15. Gluten. 



16. Glue. 



Those most used are the first seven. Tho rest are only adapted for special styles or 

 colours. The artificial gums produced by roasting starch or farina are very largely 

 in use. The action of heat on starch causes a modification in it. According to the 

 degree of heat and its duration a greater or less modification ensues ; the higher the 

 heat, the more soluble in water the gum, but also the browner and of less thickening 

 properties. The addition of various acids and alkalis to starch or farina before cal- 

 cination causes them to become soluble at lower temperatures than without : different 

 acids also produce different results ; those most generally used are nitric, acetic, 

 muriatic, oxalic, and recently lactic acid has been proposed by Pochin. The propor- 

 tion of acid used is very small, and, though the effect is produced, the acid disappears 

 during calcination. Small quantities of alkalis are also used for special modifications 

 of these gum-substitutes. The making of these gums is a distinct branch of trade, 

 and finds employment for large capital and numerous hands. In giving the receipts 

 for the various colours, care will be taken to specify the nature and proportion of 

 thickening to be employed for each colour ; a most important matter, often neglected 

 by English writers upon calico-printing. 



It is often observed that goods printed upon the same day, and with the same 

 mordant, exhibit inequalities in their tints. Sometimes the colour is strong and decided 

 in one part of the piece, while it is dull and meagre in another. The latter has been 

 printed in too dry an atmosphere. In such circumstances a neutral mordant answers 

 best, especially if the goods be dried in a hot flue, through which humid vapours are 

 in constant circulation. 



In padding, where the whole surface of the calico is imbued with mordant, the 

 drying apartment or flue, in which a great many pieces are exposed at once, should 

 be so constructed as to afford a ready outlet to the aqueous and acid exhalations. The 

 cloth ought to be introduced into it in a distended state ; because the acetic acid may 

 accumulate in the foldings, and dissolve out the earthy or metallic base of the mordant, 

 causing white and grey spots in such parts of the printed goods. Fans may be em- 

 ployed with greater advantage, combined with hot flues. See VEHTILATION. 



The mordant and thickening, or tho dye decoction and thickening, being put in one 

 of the copper pans, is stirred by hand or machinery and boiled till perfectly smooth ; 

 the steam being then shut off, cold water is admitted to the double casing, and the 

 colour cooled. It is then emptied out of the pan into a straining cloth, stretched over 

 a tub, and strained to remove all gritty particles, which would be very injurious to the 

 copper rollers. A very useful straining machine was invented a few years ago by 

 Dollfus Mieg and Co. and patented in this country. This machine is shown in 

 fig. 366. It consists of a case or cylinder, in which a piston is worked, either by 

 hand or power, to press the colour through a cloth made of cotton, linen, hair, or 

 other suitable material at the bottom of the case or cylinder ; or, instead of the said 

 cloth, a wire gauze may be used. The bottom of the piston may be made of wood, 

 copper, brass, gutta percha, caoutchouc, or other suitable material. Tho manner of 

 working the apparatus will be clearly understood by reference to the drawings, in 

 which fig. 366 is a side elevation of tho said machine or apparatus, and.^. 367 a front 

 elevation of the same. A represents tho case or cylinder, which is strengthened at 

 its upper part by the iron band B, and also at its lower part by the ring a. The 

 skeleton plate b, which forms the bottom of the cylinder, is removable, and sustained 

 by the four hooks c. To disengage the plate b, springs are fitted on the ring d, which 

 act upon two of the hooks c, so as to throw them out from under the grid b. Upon 

 the ring a the second ring d is laid, which supports the circular handle e. The upper 

 parts of the four hooks c lie upon four inclined planes fitted on the ring d. The 



